accessory sex glandsSeminal vesicles (vesicular glands, prostate and Cowper's [bulbourethral] glands) that contribute the main fluid portion to the semen.
accuracyThe reliability of a procedure; freedom from making mistakes.
acentric chromosomeAbnormal chromosome lacking a centromere.
acrocentric chromosomeChromosome with the centromere near one end.
action potentialchanges in membrance potential that characterize a nerve impulse; essentially the depolarization of a neuron.
active siteregion on an enzyme that can bind with a specific substrate or substrates.
active transportenergy-requiring process that moves material across a cell membrane against a concentration difference.
adaptationProcess of selection on heritable components of the phenotype that enhances the survival and reproductive fitness of a population.
additive genetic valueSum of average effects of gene substitutions for all loci influencing the trait of interest. Also referred to as the Breeding Value.
additive genetic varianceThat portion of the phenotypic variation attributed to differences among additive genetic values (breeding values) of individuals in a population.
additive relationshipDegree to which individuals are related as measured by the proportion of genes that are identical by descent, i.e. originating in a common ancestor.
additive theoremThe probability of the occurrence of one of several mutually exclusive events is the sum of probabilities associated with each individual event.
adenine triphosphate (atp)compound that stores energy in cells.
adeninenitrogenous base in nucleic acids, belonging to the purines; base pairs with thymine or uracil.
adjacent-1 assortmentSeparation of chromosomes in anaphase I of reciprocal translocation heterozygotes such that homologous centromeres migrate to opposite poles. Because gametes produced are all duplicative and deficient for parts of the two chromosomes involved, all gametes produced are non-viable.
adjacent-2 assortmentSeparation of chromosomes in anaphase I of reciprocal translocation heterozygotes such that homologous centromeres migrate to the same pole. Because gametes produced are all duplicative and deficient for parts of the two chromosomes involved, all gametes produced are non-viable.
age-specific survival rateProportion of individuals which survive from the beginning of one age class to the next.
age-specific survivorshipProportion of individuals which survive from birth to the beginning of a specific age class.
alkylating agentSubstance that alters DNA by adding alkyl groups.
alleleAlternate form of a gene possessing a unique nucleotide sequence. Also referred to as an allomorph.
allopatric speciationSpeciation that is associated with geographical isolation.
allopolyploidyPolyploidy originating from a combination of two or more sets of chromosomes derived from different parental species.
allosyndesisPairing of homologous chromosomes in a allopolyploid which results in chromosomes derived from one parent pairing with chromosomes derived from the other parent.
allozygousHomozygous for a gene but the homologous genes are not identical by descent.
alternate assortmentSeparation of chromosomes in anaphase I of reciprocal translocation heterozygotes such that homologous centromeres migrate to opposite poles. Because resulting gametes contain either two normal chromosomes or two translocation chromosomes from the parent translocation heterozygote, the gametes produced are not duplicative or deficient, hence all are viable.
alternation of generationsHaving two life forms during the life cycle, found in plants; the sporophyte which produce the micro and megasporocytes and the gametophyte which produces the male and female gametes.
amino acidAny one of the monomer units that are polymerized to form proteins.
amorphAn allele that does not produce a product or an effect on the phenotype.
ancestorOne from whom an individual is descended.
anchor locusA well mapped locus that serves as a marker for a particular chromosome segment.
aneuploidPolyploid individual whose chromosome complement is not comprised of an even number of the full set of the haploid chromosome number for the species.
annoymous locusPolymorphic DNA region with no known fucntion but useful in map studies for positioning loci of interest.
antherStructure which produces and releases pollen.
anthesisFlowering, time when male structure within an inflorescence is mature and pollen is shed.
antibodyImmunoglobulin produced by lymphoid cells upon exposure to a specific antigen.
anticodonThe triplet of nucleotides on a transfer RNA molecule that recognizes a particular messenger RNA codon in the ribosome during the formation of a protein.
antigenSubstance capable of inducing the production of antibodies.
artificial selectionSet of human-imposed rules designed to govern the probability that an individual, chosen on the basis of one or more traits, survives and reproduces.
artificial vaginaA device for collecting semen.
asepsisEssentially a germ-free environment.
asexual reproductionFormation of new individuals from one parental line by simple mitosis. Many plants and lower animal forms, including bacteria, can propagate without male and female gametes combining at fertilization.
assortative matingNon random mating systems that are based on phenotypes. Positive assortative mating is mating individuals with like phenotypes and negative assortative mating is mating individuals with unlike phenotypes.
autogamyThe mode of reproduction in which fusion of two haploid nuclei from the same individual results in formation of the zygote.
autopolyploidyPolyploid in which all of the chromosome sets are derived from the same parent species.
autosomal chromosomeChromosome other than the sex chromosomes.
autosomal locusLocus located on any chromosome other than sex chromosomes.
autosomeChromosome that is not a sex chromosome.
autosyndesisPairing of homoeologous chromosomes in an allopolyploid (opposite of allosyndesis).
autozygousHomozygous for a gene and the homologous genes are identical by descent.
backcrossMating of F1's (first filial generation individuals) to individuals from either parental strains.
base analogCompound similar enough to bases in DNA that it can be used in synthesis of DNA.
base pairingattraction between complemetary nitrogenous bases that produces a force that holds the two strands of the DNA double helix together.
basecompound that releases hydroxide ions in solution.
basic chromosome numberNumber of chromosomes represented by one copy of each chromosome type found in a normal somatic cell of a species.
binomialConsisting of or pertaining to two terms.
biochemical mutationMutation which affects a biochemical pathway.
bivalentPair of homologous chromosomes.
blastocystThe young embryo differentiated into a layer of cells (inner cell mass), which will become the embryo, and an outer layer of cells (trophectoderm), which will become the placenta.
blastomereAn individual cell in a young embryo that collectively make up the blastocyst.
blastomeresIndividual cells comprising the young embryo up to the blastocyst stage.
blunt endPiece of DNA that has been cleaved with a restriction enzyme which has left the 3' end of one strand flush with the 5' end of the other strand.
breed1. To propagate sexually. 2. A relatively homogenious group of individuals within a species, developed and maintained by man.
breeding valueValue of an individual in a breeding program. Also referred to as the additive genetic value.
bridge-breakage-fusion cycleProcess that begins when a chromosome with a broken end fuses with a sister strand at the broken end, and proceeds into mitosis, during which the ends break again, repeating the cycle.
capacitationFinal maturation of sperm making it fully capable of fertilizing an oocyte (egg).
carpelPart of a flower that encloses the ovules and extends into a compound pistil.
cell bodypart of a neuron that contains the nucleus and much of the cytoplasm.
cell cycleperiod from the beginning of one mitosis to the beginning of the next.
cell divisionprocess by which the cell divides into two daughter cells.
cell membranecell structure that regulates the passage of materials between the cell and its environment; aids in the protection and support of the cell.
cell specializationcharacteristic of certain cells that makes them uniquely suited to perform a particular function within the organism.
cell theoryunderstanding that all living things are composed of cells and that all cells come from preexisting cells.
cell wallcell structure that surrounds the cell membrane for protection and support in plants, algae, ans some bacteria.
cellbasic unit of structure and function in living things.
centimorganUnit of measure for distance on genetic maps. One centimorgan corresponds closely to one percent recombination.
centrioleMinute body usually found near the center of animals cells, which helps to direct chromosome movement during mitosis by formation of spindle fibers. Centrioles are not found in plant cells.
centromerePrimary constriction of a chromosome; site of spindle fiber attachment.
cervixShort structure essentially forming a gate to the interior part of the female reproductive system, the uterus.
chasmogamyFlowering system in plants in which fertilization occurs after the flower has opened.
chi-square testStatistical procedure used to test degree of association or agreement between observed results and those results expected based on the hypothesis being tested.
chiasmaPoints at which homologous chromosomes remain attached after pairing has ceased in meiosis.
chimeraA composite individual derived from the fusion of two embryos.
chromatidOne of two identical longitudinal halves of a duplicated chromosome, held together with its twin at the centromere.
chromatinSum of the DNA, RNA and protein of the chromosomes in a nucleus.
chromomereDarker staining region resulting from local coiling of DNA along the chromosome.
chromonemaSingle chain of DNA in an unreplicated chromosome with one chromatid.
chromosomal mutationchange in the number or structure of chromosomes in a cell.
chromosome mapMap of the linear arrangement of genes on a chromosome. Two types of maps are: recombinant maps, as predicted from recombination experiments and physical maps, as may be obtained from DNA sequencing.
chromosome theory of hereditytheory that states that genes are located on chromosomes and that each gene occupies a specific place on a chromosome.
chromosomeThread-like DNA structure , found in nuclei of cells, that carries hereditary material (genes).
cis-trans testTest used to determine whether two mutations affecting the same trait but with different origins lie within the same cistron.
cistronSegment of DNA which codes for a specific protein, and the start and stop signals of that segment.
cleavage divisionsFirst 4 to 6 divisions of the young embryo, multiplying the number of cells without increasing the size.
cleistogamyFlowering system in plants in which fertilization occurs within closed flowers, thereby promoting self-pollination.
clineChange in environmental variables (such as temperature) which is accompanied by a regular increase or decrease in an allele frequency.
cloneGenetically identical cells or individuals originating from a common anscestrial cell or individual.
cloningFormation of exact genetic replicas.
coadaptationProcess of selection acting on units of two or more genes.
codominanceMode of inheritance in which phenotypic expression of two different alleles occurs in the heterozygote as a result of neither allele being dominant over the other.
codonSequence of three nucleotides in messenger RNA that specifies the amino acid that is to be inserted in a specific position during the synthesis of a protein. A complementary codon is found in DNA which codes for the messenger RNA.
coefficient of coincidenceNumber of double crossovers observed by experimentation divided by the expected number of double crossovers.
coisogenicA strain established from an inbred line that differs from the inbred line by the presence of a mutation at a single locus.
colinearityCorrespondence between the location of mutant sites in bacterial DNA and the location of amino acid substitutions in the finished polypeptide or protein.
collateral relativeRelated through a common ancestor, not by a direct line of descent. Half sibs are collateral relatives.
complex locusFunctionally related genes that are closely linked hence tending to be inherited as a unit.
compound pistilFemale floral structure comprised of two or more pistils.
conception rateThe fertilization "rate" or proportion of females mated or inseminated that initiate a pregnancy. Because of embryonic death, calving rate, lambing rate, etc., are lower than the conception rate.
conditional mutationMutation resulting in a change in the phenotype which is only observed under specific environmental conditions
conditional probabilityProbability of occurrence of one event given that another event has occur.
conjugationprocess in bacteria and protists that involves an exchange of genetic information.
consanguinityRelated through at least one common ancestor.
conservative replicationModel of DNA replication in which both original strands of DNA are retained in the parent cell, while both newly synthesized strands are incorporated into the daughter cell.
contingency chi-squareA chi-square test performed for the comparison of two sets of data.
continuous variationVariation where characters are divided by small differences in metric or quantitative values across a continuum, not by counts in broadly specified classifications such as coat colors.
corpus luteumStructure that forms in the follicle if ovulation has occurred. It produces progesterone and maintains pregnancy.
correlationStandardized measure of the degree of association between two characteristics.
covarianceMeasure quantifying the degree to which two characteristics vary together.
crossMating between genetically different individuals.
crossbreedingMating of individuals from different breeds. The progeny are usually referred to as F1's, first filial generation.
crossing overExchange of segments of DNA between homologous chromosomes most often occurring during meiosis.
cytokinesisprocess by which a cellís cytoplasm divides to form two distinct cells.
cytoplasmContent of a cell excluding the nucleus.
cytoplasmic inheritanceGenes controlling a trait are located in cytoplasmic factors or within organelles in the cytoplasm. Extranuclear inheritance.
cytoplasmic male sterilityMale sterility systems controlled by the interaction of genes located in the cytoplasm (mitochondria) and the nucleus.
cytosinenitrogenous base in nucleic acids belonging to the pyrimidines; base pairs with guanine.
deficiencyAbsence of a chromosome or chromosomal segment.
degrees of freedomNumber of independent parameters required to describe some component. For categorical classifications of phenotypes associated with the genotypes at a particular locus this number is one less than the number of phenotypes.
deletionLoss of a segment of a chromosome.
deoxyribonucleic acid(DNA) - Self replicating molecule that encodes hereditary information, consisting of long chains of four different nucleotides arranged in a double helix.
dependent variableA measurable characteristic who's value is conditioned on the value of a second variable (the independent variable) and who's value may be predicted from the relationship with the independent variable.
dicentric chromosomeAbnormal chromosome or chromatid having two centromeres.
diffuse centromereSpindle fibers attach to chromosomes along their length rather than at defined centromere. This situation is normal but only found in a few species.
dihybrid test crossMating involving a parent expressing the dominant phenotypes associated alleles at two loci with an individual having recessive genotypes at both loci. The purpose is to determine the presence or absence of recessive alleles at either locus in the first parent.
dihybridIndividual heterozygous at two loci.
dioecySystem of sexual expression in plants in which individual plants bear either staminate (male) or pistillate (female) flowers, but not both. (Contrast to monoecy)
diploidPossessing a full complement of paired chromosomes.
direct relativeRelative in direct line of descent.
directional selectionSelection favoring one extreme phenotype.
disaggregationSeparation of individual cells growing together, such as the blastomeres that form a blastocyst.
disequilibriumState where genotypic frequencies at two or more loci considered jointly deviate from expected frequencies based on products of gene frequencies.
disjunctureSeparation of chromosomes during meiosis.
dispersive replicationModel of DNA replication in which the original and newly synthesized strands are distributed randomly between the parental and daughter cells.
diversifying selectionSelection favoring both extremes or two or more diverse phenotypes.
dna fingerprintingtechnique for identifying individuals using repeating sequences in the human genome that produce a pattern of bands that is unique for every individual.
dna ligaseEnzyme which catalyzes the formation of a phosphodiester bond between the 3'-OH end and the 5'-P end of a DNA molecule.
dna polymeraseEnzyme that catalyzes the production of DNA.
dna repairMechanism which corrects the nucleotide sequence of a DNA molecule that has undergone mutations, or has had its nucleotide sequence altered.
dominance deviationDeviation of the genetic value from the additive genetic value (breeding value) for genotypes at a single locus.
dominance valueSum of dominance effects of all gene pairs influencing the trait of interest.
dominanceOne allele masking the presence of another in the expression of the phenotype. The allele whose presence is masked by the dominant allele is said to be recessive.
dominantTerm for an allele that masks the presence of an other allele, with respect to phenotypic expression, when occurring together in a heterozygous individual.
dorsalupper side of an organism that has bilateral symmetry.
double fertilizationFertilization in plant species involving two fusion events, the fusion of the egg nucleus with a sperm nucleus to form a 2n zygote, and the fusion of the two polar nuclei with a sperm nucleus to create the triploid cell which will form the endosperm.
double helixDNA model discovered by Watson and Crick consisting of antiparallel strands of DNA wound into a right-handed spiral and held together by hydrogen bonds.
duplexGenotype in an autotetraploid consisting of two copies of one allele and two copies of a different allele.
duplicationAlteration in which extra copies of a chromosome or chromosomal segment are found within the nuclear genome.
effective population sizeEffective number of individuals passing on gametes to the next generations. The effective number is equivalent to a population of that size in which an equal number of males and females contribute to the next generation.
eggFemale germ cell (ovum) carrying a haploid (single) set of genes.
ejaculateThe semen produced when a male is stimulated to expel the sperm and seminal fluids externally.
embryo splittingDividing an embryo microsurgically into equal halves to produce identical twins.
embryo transferTransfer of an embryo from a donor female or an embryo created by fertilization and culture in vitro and transferred to a recipient female for development into young.
embryoThe young conceptus following fertilization during cleavage until organs start to form. Then it is called a fetus.
embryonic lethal genotypeGenotype whose expression results in the prenatal death of the individual possessing it.
embryonic stem cellsLine of cells maintained in vitro, each with the potential to develop into a new individual.
endonucleaseEnzyme that breaks the phosphodiester bonds in a DNA molecule.
endoplasmic reticulumcomplex network that transports materials throughout the inside of a cell.
endospermIn angiosperms, the triploid cells which nourish the embryo during development. These cells are formed by the fusion of two polar nuclei with one sperm nucleus.
enucleationRemoval of the nucleus from a cell.
environmentComposite of all non-genetic factors influencing the phenotypic expression of a trait.
enzymeone of a number of special protein catalysts contained in living organisms.
epididymisA duct from each testicle, with parts called the head, body, and tail, that stores and transports sperm to the vas deferens.
episomeOne of a class of genetic elements that, after insertion into a host cell, may replicate autonomously in the cytoplasm of the host, or become integrated into the chromosome of the host cell, and be replicated along with it.
epistasisInteractions between genes at two (or more) loci affecting the phenotypic expression of a trait.
epistatic effectSum of effects due to combinations of alleles at different loci interacting to influence the trait of interest.
equational divisionDivision seen in mitosis and in anaphase II of meiosis whereby each chromosome separates into equal longitudinal halves through separation of sister chromatids.
equilibriumState in which gene and genotypic frequencies remain constant in a population from one generation to the next.
estrous cycleThe reproductive cycle of a female characterized by ovulation and acceptance of the male at regular intervals.
ethicsThe science or discipline involving the principles of right versus wrong. It requires a moral judgment in practice.
eukaryoteOrganism which possess a membrane bound nucleus that contains the organism's chromosomes.
euploidPolyploid individual whose chromosome complement is comprised of a whole number of its basic chromosome set.
eventOccurrence of whatever it is stated to be.
evolutionprocess by which modern organisms have descended from ancient organisms; any change in the relative frequencies of alleles in the gene pool of a population.
exclusive eventsEvents for which the occurrence of one precludes the occurrence of the other.
exonSegment of DNA that is translated into protein.
expected numberPrediction of the number of observations occurring for an event based on the probability of the event given the hypothesis being tested and the total number of observations in the sample.
explantRemoval of a piece of tissue from a living organism for use in a tissue culture.
expressivityVariation in the degree to which a phenotype for a particular genotype is expressed within an environment or across different environments.
facilitated diffusiondiffusion of materials across a cell membrane assisted by carrier molecules.
family selectionSelection scheme in which whole families are selected.
fecundity rateAverage number of same-sexed offspring produced by an individual in a specific age class.
fertilizationFusion of the sperm nucleus with the egg nucleus.
first filial generationFirst generation of progeny produced from the mating of different purebreeding strains. Referred to as F1's.
fitnessCapability of a genotype to survive and reproduce. Selection, within environments, acts against the phenotype associated with the genotype.
fixationEvent defined by an allele at a particular locus reaching a frequency of one in the population. Other allele frequencies are, by definition, zero and these alleles are said to be lost to the population.
flanking markersGenes, used in tandem as genetic markers, that are located at opposite ends of the DNA sequence or segment of chromosome being monitored.
follicleOvarian structure that stores the ovum and secretes female hormones.
forward mutationMutation from wild type to a mutant allele.
frameshift mutationMutation in which the reading frame used in translation is skewed, so that many codons are incorrectly read.
frameshiftBase pair insertion or deletion that results in a shift in sequence of reading codons.
frequencyProportion of observations occurring for an event.
frozen embryosEmbryos carefully frozen, usually as blastocysts, and stored in liquid nitrogen until recipients are ready.
frozen spermSperm carefully preserved in liquid nitrogen at -196 degrees C.
full sibBrother or sister having both parents in common.
gameteMature, haploid reproductive cell.
gametic chromosome numberNumber of chromosomes found in a normal gamete; usually half the number of chromosomes found in a somatic cell.
gametogenesisProduction of gametes.
gametophyteLife form in the life cycle of a plant which produces the male and female gametes. The male gametophyte is the mature germinated pollen grain, the female gametophyte is the mature ovule.
gene by environment interactionEvent for which the phenotypic expression associated with a particular gene or genotype dependents on the environment in which the individuals with the genotype exists.
gene conversionSituation in which products of meiosis from an AA' individual are 3A and 1A', or vice versa, giving the impression that one A gene has been converted into an A' gene, or vice versa.
gene frequencyProportion of genes at a locus represented by a particular allele.
gene mutationchange involving the nucleotides of DNA.
gene poolTotal complement of genes in a population.
geneUnit of heredity. Segment of DNA found at a particular position (locus) on a chromosome, involved in expression of a specific trait.
genealogyRecord of descent tracing genetic relationships of individuals.
generation intervalThe time elapsing from reproduction in one generation to the time the next generation reproduces.
generation turnoverTime between parents producing offspring and those offspring reaching reproductive age.
generationCohort of individuals born and living at the same time.
genetic codeSequence of three nucleotides in DNA or RNA that specify amino acids.
genetic contributionThe contribution of genetic material by a parent to progeny, usually measured in animal breeding as a specified improvement in the population for a particular trait such as milk production.
genetic driftRandom fluctuation in gene frequencies occurring as a result of gamete sampling, particularly noticeable in small populations.
genetic engineeringManipulating genetic material of organisms in order to produce desired effects.
genetic loadAverage number of lethal alleles per individual in a population.
genetic markerGene used to follow the inheritance of a particular sequence of DNA or segment of chromosome.
genetic varianceComponent of the phenotypic variation attributed to differences in the genotypes of individuals in the population. Is the sum of the additive, dominance and epistatic variance.
geneticInfluenced or produced by genes.
geneticsStudy of heredity.
genomeFull complement of genes carried by the cell.
genotypeFull complement of genes influencing the phenotype for a particular trait.
genotypic frequencyProportion of individuals in a population with a particular genotype.
genotypic ratioRatio of genotypes in progeny from matings involving parents with specified genotypes.
genotypic valueValue of a genotype measured for a single locus as the phenotypic value associated with the genotype minus the average phenotypic value of the two homozygotes.
genusgroup of closely related species.
germ cellBasic reproductive cells that give rise to sperm in the testes and oocytes in the ovary.
germ plasmGeneral term for germ cells or often referring to the whole genotype.
glans penisTip of the penis with sensory nerve endings.
golgi apparatusorganelle that modifies, collects, packages, and distributes molecules made at one location of the cell and used at another.
gradualismtheory that evolutionary change occurs slowly and gradually.
guaninenitrogenous base in nucleic acids belonging to the purines; base pairs with cytosine.
hair follicletubelike pocket of epidermal cells that extends into the dermis and produces hair.
half sibBrother or sister having one parent in common. Paternal half sibs have a common male parent and maternal half sibs a common female parent.
haploidHalf ploidy. Containing half of the number of each chromosome as is found in normal somatic cells for a species.
haplotypeParticular combination of closely linked alleles that tend to be inherited as a unit.
hardy-weinberg equilibriumState of a population in which the gene and genotypic frequencies remain constant from one generation to the next.
hardy-weinberg lawPrinciple in population genetics stating that gene and genotypic frequencies remain constant from one generation to the next assuming: 1. The population is large. 2. There is random mating. 3. There are no forces that change gene frequencies (mutation, migration, and selection).
hemizygousGene present in a single dose as is found, for example, at sex linked loci in the heterogametic sex.
hereditaryCapable of being passed, through genetic material, from one generation to the next.
heredityTransmission of characters through genetic material from one generation to the next.
heritabilityProportion of the phenotypic variation attributed to genetic variation . Heritability in the broad sense is the proportion of phenotypic variation attributed to differences among genotypes of individuals and heritability in the narrow sense is the proportion of the phenotypic variation attributed to differences among breeding values of individuals .
heritableCapable of being inherited.
hermaphroditicPossessing both male and female reproductive organs.
heterogameticContaining one each of the two forms of the sex chromosome.
heteromorphicHomologous chromosomes that differ in morphology.
heterosisIncreased vigor or performance observed in the heterozygous progeny that result from matings of homozygous or purebreeding parental lines. Heterosis is a function of non-additive genetic components, dominance and epistatic effects. Also referred to as hybrid vigor.
heterostylySpecific flower morphology in which stamens and styles are of unequal lengths, thereby promoting cross-pollination.
heterozygoteIndividual having unlike alleles at a locus. See heterozygous.
heterozygousorganism that has two different alleles for the same trait and is said to be hybrid for that particular trait.
holliday modelModel describing the series of breakage and reunion events occurring during crossing over of two homologous chromosomes.
homoeologous chromosomesChromosomes which are similar in that they carry most of the same loci but are not fully homologous since they are derived from different, though related, species.
homogameticContaining two copies of one form of the sex chromosomes.
homogeneity chi-squareChi-square test used to individually test several data sets for fit to an expected ratio or to determine whether different sets of data are homogeneous (give the same results) so that the data sets may be pooled.
homologCharacteristic that are similar across species having originated from a common ancestor.
homologous chromosomesChromosomes with identical content of gene loci.
homozygoteIndividual having pairs of like alleles at a locus. See homozygous.
homozygousHaving like alleles at the same locus.
hybridProgeny resulting from mating different purebreeding strains; referred to as F1's (first filial generation).
hybridizationInterbreeding of different strains.
hyperploidDuplicated locus or chromosome segment in an individual containing a duplication.
identical by descentCase where two genes originate as replications of the same gene in a common anscestor.
immigrantOne who moves into a new habitat.
immigrateTo enter into a new habitat.
immunoglobulinGlycoprotein produced by lymphiod cells, specifically B Cells, upon exposure to a specific antigen. Exist as either membrane bound or secreted (antibody).
immunosurgeryUsing immune sera selectively to destroy certain cells to evaluate others. Used for selective staining.
in vitro fertilizationFertilization done in the lab in a culture dish.
in vivoProcesses that occur in the living organism, in contrast to those performed in the laboratory (latter is in vitro, i.e. in glass).
inbreeding coefficientProbability that both alleles at a particular locus are identical by descent.
inbreedingMating of related animals resulting in a non-zero probability that alleles at a particular locus are identical by descent. The probability of alleles at a locus being identical by descent is one-half the additive genetic relationship between the parents.
incomplete dominanceinheritance in which an active allele does not entirely compensate for an inactive allele.
incomplete penetrancePhenotype associated with a particular genotype is not always expressed, perhaps due to compensating factors in the environment.
independent assortmentprocess by which genes segregate independently.
independent eventsEvents for which the probability of one event occurring is not influence by the occurrence of the other event.
independent variableA variable that influences the measure of a second characteristic (the dependent variable).
independentThe probability of the an event occurring is not influenced by the occurrence of another event. The joint probability of the two independent events is the product of their individual probabilities.
induced mutationMutation resulting from deliberate use of mutagens.
inducerOrganic molecule which activates transcription of an operon by deactivating the repressor protein.
inflorescenceStructure including flowers in the angiosperm.
infundibulumFunnel-shaped end of the oviduct conveying the egg (or eggs) from the ovary into the oviduct.
inheritanceGenetic characters transmitted from one generation to the next.
inner cell massPart of a blastocyst that will form the embryo.
insertionMutation caused by the addition into a DNA sequence of one or more base pairs.
inter seAmong themselves.
interallelic interactionInteraction of alleles at different loci to produce a phenotype.
intercalating agentSubstance which inserts itself into DNA in spaces between bases.
interferenceWhen the occurance of a crossover in a region of DNA reduces the probability of a second crossover in the same region.
intergenic interactionInteraction of two or more loci to produce a phenotype.
interphaseperiod of the cell cycle between cell divisions.
interstitial crossoverCrossover between a centromere and the translocation point.
intragenic interactionInteraction of two alleles at one locus to produce a phenotype.
intronintervening sequence of DNA that does not code for a protein.
inversionReversal in the orientation of a segment of DNA within a chromosome.
isogamycondition in which the gametes of a species appear identical.
isogenicGenotypically identical.
karyotypeA display of the chromosomes of an individual, showing number and morphology.
known carrierIndividual who is known to carry a recessive gene at a particular locus
law of independent assortmentGenetic factors that influence one trait segregate independently from those that influence a second trait.
law of segregationGenetic factors appear in pairs within an individual. A random member of the pair is passed from parent to progeny.
leptotene stageStage in meiotic prophase in which the diploid number has already been doubled, chromosomes appear as thin threads with clearly defined centromeres, and are oriented such that one or both of their ends are in contact with one region of the nuclear membrane.
lethal genotypeGenotype whose expression results in the death of the individual possessing it.
ligaseEnzyme that forms a bond between one carbon and another, or between a carbon and a sulfur, oxygen, or nitrogen via condensation reactions that use energy from adenosine triphosphate (ATP).
linebreedingSystem of mating which maintains close relationships in descendent generations to a particular ancestor.
linkageClose physical proximity of two or more genes on a chromosome which results in them to tend to be inherited together.
locusPosition of a single gene on a chromosome.
lymphocyteWhite blood cell found in lymphoid tissue and blood. There are two types: B cells, which are associated with production of antibodies and T cells, which mediate immune recognition.
lysogenic infectionprocess in which viral DNA in inserted into the DNA of a host cell where it can remain for many generations before becoming active.
lysosomeOrganelle responsible for digesting and degrading a variety of substances in the cell.
macrosporocyteCell which undergoes meiosis to generate the meiotic products that become ovules.
map distanceDistance between genes expressed as centimorgans (corresponding to a recombination frequency of 1%).
markerGene used to identify a segment of DNA.
mass selectionSelection based on individuals (their own phenotypic performance).
maternal effectEffect on progeny performance associated with the maternal environment provided by the maternal parent.
maternal half sibBrother or sister having the same dam but different sires.
megasporogenesisProcess of producing the megaspores.
meiocyteCell whose nucleus is destined to enter meiotic prophase.
meiosisProcess during gametogenesis by which the number of chromosomes per cell is reduced to the haploid number (one-half the full complement of chromosomes).
mendelGregor Johann Mendel, Austrian Monk, 1822-1884. Recognized as the founder of the principles of genetics.
mendelian characteristicTraits for which the phenotypic expression is controlled by relatively few loci segregating in a Mendelian fashion.
meristem cultureSterile growth of meristem of angiosperm. Can be used to asexually maintain or propagate plants with a desired genome.
messenger rnaResults from transcription of a gene, and contains the genetic information necessary to direct synthesis of a specific polypeptide chain.
metacentric chromosomeChromosome with the centromere near the center.
metafemaleFemale with more than two X chromosomes.
metaphase plateEquator of the spindle at which the chromosomes group during the metaphase stage of mitosis.
metaphasesecond phase of mitosis in which the chromosomes line up across the equator of the cell.
methylationAddition of a methyl group to a molecule.
metric characterCharacteristics that are measures not counts (e.g., height of an individual). Quantitative genetics deals with metric characteristics.
microsporocyteCells which undergoes meiosis to generate the meiotic products that become pollen grains.
microtubuleCytoplasmic structure consisting of the protein tubulin and involved in cellular structure and movement.
microvilliProjections from the cell surfaces of an embryo involved in the exchange of gases and nutrients.
migrationMovement of breeding individuals or their gametes from one population to another.
mimicAlleles at different loci that produce the same phenotype.
minimum viable populationAbbreviated MVP. Lower limit for carrying capacity in captive populations. Depends on the genetic and demographic objectives and the biological characteristics of the population.
missense mutationChange in the base pair such that a codon indicates insertion of a different amino acid in translation.
mitochondriaOrganelle responsible for the production of cellular energy via oxidative phosphorylation.
mitochondrionOrganelle in the cytoplasm associated with formation of adenosine triphosphate (ATP).
mitosisProcess of cell division which results in formation of two daughter cells identical in chromosome number and complement to the original mitotic cell.
mitotic spindleCollection of microtubules responsible for controlled movement of chromosomes during mitosis.
monoecySystem of sexual expression in plant species in which individual plants bear staminate (male) and pistillate (female) flowers that are physically seperated on the same plant..
monohybrid crossMating of two strains homozygous for different alleles at a single locus.
monosomicHaving one less chromosome than the normal diploid number; missing a chromosome of one homologous pair.
monozygotic twinsIndividuals arising from a the splitting of a single zygote, hence having identical genotypes.
morganRecombination distance of 100 percent. One Morgan is 100 centimorgans (cM). A cM is equivalent to one percent recombination.
mortality rateProportion of individuals that die in a specific age class. Calculated as the number of individuals that die within the age class, divided by the number that were alive at the time defining the beginning of the age class.
morulaThe ball of cells forming the young embryo as a result of 4 to 6 cleavage divisions.
multiple allelesMore than two alleles existing in the population for a particular locus.
multiple ovulation and embryo transferA program to increase progeny from the best animals as rapidly as possible.
multiplicative theoremThe joint probability for two or more independent events is the product of the individual probabilities of the individual events.
mutagenSubstance that increases mutation rate.
mutagenesisThe process of inducing mutations through use of mutagens.
mutation rateCharacteristic rate for which one allele mutates to an alternate form.
mutationHeritable change in DNA that alters the genetic information carried by the cell, leading to a potential alteration of a genetically controlled phenotype.
mutonSmallest unit of DNA in which a change can result in a mutation.
n-formyl methionineStarting amino acid in the synthesis of all bacterial polypeptides.
natural selectionEnvironmental influence on the probability a particular genotype survives and reproduces, based on the fitness of the phenotype associated with the genotype.
natural serviceActual mating between males and females in contrast to artificial insemination.
negative assortative matingMating of individuals with unlike phenotypes.
negative controlSystem in which expression of a gene (or genes) is prevented by a controlling factor which binds to DNA, preventing transcription of the gene (or genes).
non-tandem duplicationAberration in which the duplicated segment of a chromosome is not adjacent to the original copy.
nondisjunctionCase in which homologous chromosomes during meiosis I, or sister chromatids during either meiosis II or mitosis, fail to separate at anaphase, resulting in polysomy.
nonrecurrent mutationMutation that occur only once.
nonsense mutationChange in a base pair such that a codon indicates a stop codon.
nuclear envelopemembrane that surrounds the nucleus of a cell.
nuclear transferTransfer of a nucleus or small blastomere to an enucleated oocyte. Multiple transfers (1 per oocyte), if successful, multiple clones (nearly identicals) will result.
nucleic acidChain of nucleotides.
nucleinMixture of nucleic acids and protein, originally isolated from white blood cells.
nucleolusNuclear structure rich in RNA.
nucleosidePurine or pyrimidine base attached to ribose or deoxyribose sugar.
nucleosomeBasic unit of organization of a mammalian chromosome, consisting of DNA wound around an octamer of histone proteins.
nucleotideBasic unit of nucleic acid structure composed of a 5-carbon sugar (deoxyribose, in DNA), a phosphate group, and either a purine (adenine and guanine) or pyrimidine (thymine and cytosine) base.
nucleusMembrane-bound structure found in all eukaryotic cells that contains DNA for the cell in the form of chromatin.
nulliplexIn autopolyploides, lacking any copies of a reference allele at the locus of interest.
nullisomicCondition in which both members of a chromosome pair are missing.
oncogenecancer-causing gene.
oocyteThe most mature cell type of a female germ cell which, if fertilized by a sperm cell can form a new individual.
oogenesisformation and maturation of the egg.
operatorRegion located at one end of an operon to which a repressor binds, controlling the transcription of adjacent cistrons.
operonGroup of one or more functionally related cistrons that are controlled by the same operator gene.
organellecell structure that performs a specialized function within the cell.
ovarian aspirationRemoval of oocytes through a needle inserted into a follicle of the ovary with suction applied to the needle.
ovaryPrimary sex organ in the female, producing eggs (actually oocytes) and hormones.
overdominanceMode of inheritance for which the heterozygote is favored by selection, hence is most fit.
oviductsTube from the ovary to the uterus. The egg is fertilized here if the animal is mated or inseminated at the right time.
ovuleFemale gametophyte, which donates the egg and two polar nuclei for double fertilization in plants.
ovumThe mature female gamete often called the egg.
pachytene stageStage in meiotic prophase in which each paired chromosome separates into its two component chromatids, after which crossing over occurs.
panmixisRandom mating.
paracentric inversionInversion which does not include the centromere in the inverted segment.
partial dominanceInteraction of two alleles at a given locus to produce an intermediate phenotype.
particulate theoryTheory proposed by Mendel that genetic material is comprised of distinct units (genes) and these units maintains their integrity over generations.
paternal half sibBrother or sister having the same sire but having different dams.
pedigree indexEvaluation of an individuals genetic merit based solely on the genetic evaluations of its parents ( the average of parent evaluations).
pedigreeBiological relationship among members of a family.
penetranceProportion of individuals displaying the expected phenotype based on their genotype.
penisMale organ of copulation.
peptide bondBond between two amino acids, linking the amino group of one with the carboxyl group of another.
performance testObtaining a phenotypic measure on an individual for the purpose of assessing its genetic merit.
pericentric inversionInversion containing the centromere in the inverted segment.
permanent environmental effectNon-genetic effect which influences all observations on an individual for the same trait, hence causing an additional covariance between the repeated measures.
phenocopyResult of an environmental influence which mimics the effect of a specific allele not possessed by the individual; not transmissible.
phenotypeObservable characteristics, determined by the individual's genotype and its environment.
phenotypic ratioRatio of phenotypes in progeny resulting from matings involving parents with specified genotypes.
pinType of distylic flower possessing a long style and short anthers.
pistilFemale floral structure comprised of the ovary, style and stigma.
pistillatePertaining to the pistil. Pistillate flowers contain only carpels, and so are female flowers.
plasmidGenetic element that is not part of the chromosome in bacterial species; it is a closed double-stranded DNA molecule that replicates autonomously in the cytoplasm of a prokaryotic or eukaryotic cell.
pleiotropyInfluence of a single gene on more than one different traits.
ploidyNumber of copies of the basic chromosome set found in normal somatic cells of a species.
point mutationMutation involving only one nucleotide pair.
polarityAs the embryo develops, cells differentiate to produce various parts. Each cell loses the ability to produce a whole individual. The embryo becomes polar.
pollenMale gametophyte, which donates sperm nuclei for double fertilization in plants.
pollinationTransfer of pollen to the stigmatic surface of the pistil.
polygenicTrait for which variation in phenotypes is influenced by genes at many loci.
polymorphismTwo or more alleles existing in a population at a particular locus.
polypeptidePolymer of amino acids linked together by peptide bonds.
polyploidHaving three or more sets of the basic haploid complement of chromosomes.
polyploidyCondition in which an individual possesses three or more complete sets of chromosomes.
polysomyPresence of extra chromosomes, not being a multiple of the haploid number.
population geneticsStudy of genetics in populations concerned with gene and genotypic frequencies and how frequencies change from one generation to the next.
populationGroup of individuals sharing a gene pool.
positive assortative matingMating of Individuals with like phenotypes.
positive controlSystem in which expression of a gene (or genes) is enhanced by the binding of a specific molecule to the promoter region.
pregnancy rateThe percentage of females exposed (inseminated or receiving an embryo) that sustain the development of a fetus.
prevalenceFrequency of a phenotype in the population
primary structureLinear sequence of subunits in a protein or nucleic acid.
probability of detectionLikelihood of observing the presence of a recessive allele in a individual by progeny testing. The probability that at least one progeny, out of n observed, will show the recessive genotype.
probabilityFrequency of an event in an number of repetitions of an experiment.
progeny testMating of an individual to obtain progeny for observation for the purpose of obtaining information about that individual's genotype or genetic merit.
progenyThe offspring of parents or often offspring of a sire or dam.
prokaryoteMicroorganism lacking a membrane-bound nucleus to contain its chromosomes.
promoterRegion of DNA at one end of a gene or operon to which RNA polymerase binds in the initiation of transcription.
protandryMaturation of the male organs before that of the female organs. In animals, the appearance of males preceding the appearance of females during the breeding season.
protogynyMaturation of the female organs before that of the male organs. Sequential hermaphroditism in which the female reproductive organ functions before the male.
protoplast fusionTechnique involving the merger of two cell types into a single cell.
protoplastSingle plant cell minus its cell wall.
punnett squareDiagrammatic representation of the union of gametes in all possible combinations.
purebredParent, that when inter se mated to members of the same breed or strain produces progeny with a consistent phenotype, which is also that phenotype of the parent.
purineNitrogenous base consisting of a double ring structure. Purine bases of DNA and RNA are adenine and guanine.
pyrimidineNitrogenous base consisting of a single ring structure. In DNA, cytosine and thymine are the pyrimidine bases, while in RNA, uracil is substituted for thymine.
quadruplexAutotetraploid possessing four copies of the same allele at a particular locus. (see nulliplex)
qualitative traitTrait controlled by relatively few loci, such that each allele has a marked effect on the phenotype and individuals can be classified phenotypically into one of a few groups.
quantitative traitTrait controlled by many loci each having a relatively small effect on the variation observed among phenotypes.
quartetGroup of four nuclei which is the result of two meiotic divisions.
quaternary structureWay in which two or more polypeptide chains fit together to form a protein.
random genetic driftRandom fluctuations in gene frequency both in direction of change and magnitude of change due to gametic sampling. Of particular concern in small populations.
random matingMating system in which any individual of one sex is equally likely to mate with any individual of the opposite sex with respect to one or more traits; also referred to as panmixis.
random sampleSample of individuals drawn without regard to any specific criteria e.g., phenotype, genotype or relationship to other individuals.
recessiveBeing masked by a dominant allele.
reciprocal crossCross in which females of genotype A are mated to males of genotype B and males of genotype A are mated to females of genotype B; useful in detecting sex-linkage, maternal effects, and cytoplasmic inheritance.
recombinant dnaDNA molecule that forms from the combination of portions of two different DNA molecules.
recombinant chromosomeChromosome resulting from crossing over of genetic material from its homologous chromosome.
recombinantIndividual with gene combinations different for the parent gene combinations due to recombination by either independent assortment or crossing over.
recombinantsFraction of new combinations appearing in each generation.
recombinationFormation of new gene combinations through the process of independent assortment or crossing over and exchange of genetic material between homologous chromosomes.
reconSmallest unit of DNA capable of recombination.
recurrent mutationMutational event with characteristic mutation rates.
reductional divisionType of division seen in anaphase I of meiosis, during which paired chromosomes separate. Reductional division is not found in mitosis, since chromosomes are not paired.
regenerationRestoration of tissue by repair or regrowth.
regression equationEquation using regression to predict the value of a dependent variable from a known value of the independent variable.
regressionA statistic that describes the relationship of two variables. The regression coefficient measures the expected change in a dependent variable per unit change in the independent variable.
regulator geneGene which controls expression of other genes through synthesis of repressor proteins.
relative fitnessCapability of a genotype to survive and reproduce. Expressed as proportion to the most fit phenotype.
relative frequencynumber of times and event (allele) occurs compared with the number of times another event (other alleles for the same gene) occurs.
repeatabilityMeasure of the degree of association between repeated measurements for the same trait obtained on the same individual. Correlation between the any two of the repeated measures.
replicationProcess by which something is duplicated by following a template.
repressorProtein that binds to an operator gene, blocking transcription of the operon.
reproductive isolationseparation of populations so that they do not interbreed to produce fertile offspring.
reproductive rateThe number of progeny produced by a parent per unit of time as per year.
restriction enzymeBacterial enzyme which cleaves foreign DNA strands within specific recognition sequences.
retrovirustype of virus that contains RNA as its genetic information.
reverse mutationMutation from the mutant allele back to the wild type.
reverse transcriptaseEnzyme similar to DNA polymerase, but which uses an RNA strand as a template.
rho factorProtein found in E. coli that aids in termination of transcription by attaching to certain sites on DNA.
ribonucleic acidSingle stranded polynucleotide containing ribose sugar and an uracil nucleotide base.
ribosomal rnaForms complexes with ribosomal proteins to form ribosomes.
ribosomeCellular structure composed of RNA and protein that is responsible for protein synthesis.
ribosomeorganelle in which proteins are made.
rna polymeraseEnzyme that transcribes an RNA molecule using a DNA strand as the template.
sample sizeNumber of individuals drawn from a larger pool of individuals.
sampleA collection of individuals or measurements obtained from a larger aggregate. Results from analysis of characteristics of the sample are used to make inferences about the larger aggregate.
sampling variationChance differences in statistics describing a set of observations that occurs when repeating the experiment with a new sets of observations.
scrotal circumferenceSimple maximal circumference measured around the central portion of the paired testes.
scrotumSkin and associated tissues surrounding the testes.
second filial generationProgeny resulting from inter se mating F1 (first filial generation) individuals.
secondary sex characteristicsex characteristic that appears at puberty.
secondary structureSpecific configuration, caused by hydrogen bonds along its length, of a polypeptide within a protein; it may take on an alpha-helix, beta-pleated sheet, or a mixed configuration.
segregationSeparation of alleles at meiosis.
selection indexProcedure used to find appropriate weights for records (one or more traits) of an individual and its relatives and to combine information into a single value to rank individuals for selection.
selection intensityThe proportion of a population of tested animals that are selected and saved for breeding purposes.
selectionProcess of choosing parents for the next generation. Selection may be natural selection, reflecting the survival of the fittest, or artificial selection, a set of human-imposed rules determining with individuals are to survive and reproduce.
selective breedingmethod of improving a species by choosing animals or plants that have desirable characteristics to produce offspring that have the parentsí desirable traits.
self incompatibilityA system that prevents the production of viable offspring by self-fertilization.
semenSeminal fluids plus sperm from the male reproductive system.
semi-conservative replicationModel of DNA replication in which one of two original strands of DNA is retained in the parent cell, while the other is incorporated into the daughter cell.
seminiferous tubulesTubules in the testis where the spermatozoa are formed.
semisterilityCondition which results when there is an absence of interstitial crossover, 50% of the assortments are alternate, 25% are adjacent-1, and 25% are adjacent-2, producing 50% viable gametes and 50% non-viable gametes.
sex chromosomeChromosome associated with the determination of sex.
sex influencedTrait controlled by a gene at an autosomal locus but whose phenotypic expression in the heterozygote depends on the sex of the individual.
sex limitedTrait for which a phenotype is expressed in only one sex.
sex linkedTrait controlled by genes located on the sex chromosomes.
sexing embryosRemove one cell from a young embryo, multiply the DNA by a polymerase chain reaction, and with the correct probe, test for the Y chromosome.
sexing spermDetermining whether the sperm cell contains an X chromosome (produces a female) or a Y chromosome (produces a male).
sexual reproductionprocess in which two cells, normally from different individuals, unite to produce the first cell of a new organism.
sibBrother or sister. A full sib if both parents are in common and a half sib if only one parent is in common.
sigma factorPolypeptide of RNA polymerase of E. coli that recognizes certain binding sites on the DNA molecule for initiation of transcription.
silent mutationNucleotide change that does not alter the amino acid product.
simplexAutotetraploid possessing only one copy of a reference allele. The other three copies will be of other alleles.
sister chromatidsIdentical copies of a chromosome, formed during DNA replication, and held together at the centromere.
somatic cellCell that is not involved in the production of gametes.
speciesgroup of organisms that share similar characteristics and can interbreed with one another to produce fertile offspring.
sperm motilityThe proportion of sperm swimming, or other measures of sperm movement.
sperm productionRefers to the number of sperm produced or, in practice, sperm collected per ejaculate or per unit of time.
spermGerm cells carrying a haploid (single) set of genes from the male.
spermatogenesisThe total process involving transformation of spermatogonia into spermatids and by spermiogenesis into mature sperm.
spermatogoniaSpecialized testicular cells that, by mitosis, give rise to spermatocytes and further divide by meiosis to produce spermatids.
spindle fiberMicrotubular filament making up a collection of microtubules that govern movement of chromosomes during mitosis in eukaryotes.
spindleFiber formed during nuclear division that aligns chromosomes and pulls them to the opposite poles.
spontaneous mutationMutation which occurs naturally, as a result of damage to DNA.
sporophyteLife form during the life cycle of a plant which produces the micro- and megaspores
stabilizing selectionSelection favoring the intermediate phenotype or individuals near an optimum level of performance rather than at either extreme.
stamenPollen-bearing organ of an angiosperm flower.
staminateReferring to the stamen. Staminate flowers contain only the stamens, and so are male flowers.
standard deviationMeasure of variability, obtained as the square root of the variance. Used to describe the dispersion of observations.
sticky endDNA which has been cleaved by a restriction enzyme and has left the 5' end of one strand protruding past the 3' end of the other strand.
stigmaSurface on the style of a flower on which pollen cells germinate.
strainIndividuals kept in a closed breeding group in order to maintain particular characteristics.
stratificationSubpopulations of individuals within a larger population.
structural geneGene that codes for a protein or RNA.
stylePart of the pistil arising from the ovary , and through which the pollen tube passes.
subpopulationSubgroup of individuals isolated from other member of the larger or total population.
superovulationOvulation of a large group of oocytes (eggs) by a female as a result of hormonal stimulation.
synapsisPairing of homologous chromosomes during meiosis.
synchronyUsed normally to denote that the donor and recipient of embryos are at the same state of the estrous cycle.
syntenicLoci located on the same chromosome.
tandem duplicationAberration in which duplicated segment of DNA follow the original copy and the genes lie in the same orientation.
telocentric chromosomeChromosome in which the centromere is at an extreme end.
telophasefinal phase of mitosis, during which chromosomes uncoil, a nuclear envelope reforms around the chromatin, and a nucleolus becomes visible in each daughter nucleus.
temporary environmental effectEffect which influences only a single observation on an individual.
tertiary structureThree dimensional configuration occurring when a polypeptide is folded in on itself.
test crossProcedure for distinguishing between homozygous and heterozygous individuals for traits with complete dominance by breeding them to individuals that are homozygous recessive for that trait.
testesPrimary sex organs of the male, producing sperm cells and hormones, particularly testosterone.
tetradFour haploid cells that are the result of a single meiotic cycle.
tetraploidRefers to cells in organisms possessing four times the haploid chromosome number. Tetraploid results from the union of diploid gametes from both parents.
tetrasomicDiploid organism possessing four copies of one chromosome.
third filial generationProgeny resulting from the crossing of two second filial, F2, generation individuals.
three quarter sibSib with one parent in common and one grandparent of the second parent in common, e.g., paternal half sibs with the same maternal grandsire.
three-point crossTest designed to determine the order of three linked genes on a chromosome based on observations of the recombinants occurring from crossovers.
thrumType of distylic flower possessing a short style and long anthers.
thyminenitrogenous base found in DNA but not in RNA; base pairs with adenine.
ti plasmidTumor-inducing plasmid of the bacterial pathogen Agrobacterium tumiefaciens which is used to introduce foreign DNA into chromosomes of plants.
tissue cultureProcess of growing some part of a plant or animal on an artificial medium.
traitcharacteristic that a living thing can pass on to its young.
transcriptionRNA formation from a DNA template by complementary base pairing.
transfer rnaRecognizes and binds to specific amino acids and carries them to the ribosomes.
transformationProcess by which genes are transferred from one bacterial strain to another in the form of soluble fragments of DNA.
transgenicAn animal resulting from a gene inserted into the cell from which the animal developed. The gene did not come from a parent.
transition mutationMutation in DNA wherein a pyrimidine is replaced with a pyrimidine, and a purine is replaced with a purine.
translationFormation of a protein at a ribosome; the amino acid sequence of the protein is directed by a specific messenger RNA molecule.
translocationAberration caused by the change in location of a segment of a chromosome.
transmitting abilityOne-half the breeding value of an individual. Represents the average genetic value of gametes produced by that individual.
transposonSequence of DNA which is capable of replicating itself independent of replication of the nuclear genome, of excising itself from its current location in the genome, and of inserting itself elsewhere in the genome.
transversion mutationMutation in DNA wherein a pyrimidine is replaced with a purine, and a purine is replaced with a pyrimidine.
triplet codeSequence of three nucleotides coding for a specific amino acid.
triplexAutotetraploid possessing three copies of the reference allele and one other allele at a particular locus.
triploidRefers to cells of organisms that have three sets of the basic haploid complement of chromosomes.
trisomicDiploid organism possessing an extra (third) copy of a chromosome.
trophectodermThis is the outer layer of cells in the blastocyst that will contact the lining (endometrium) of the uterus forming the trophoblast giving rise to the placenta. This connects the fetus to the mother.
tubulinProtein that makes up microtubules.
uracilnitrogenous base found only in RNA; base pairs with adenine.
urethraCommon duct in the penis for passage of sperm and urine, normally controlled so that only sperm pass at ejaculation.
uterine hornPortion of the uterus connecting to the oviduct on each side of the female and is where the egg now developing into a young embryo will attach and grow during pregnancy.
uterusTwo uterine horns connect the body of the uterus to the oviducts.
vacuoleorganelle that stores materials such as water, salts, proteins, and carbohydrates.
vaginaExternal canal of the female reproductive system attached to the cervix.
varianceMeasure of the degree of dispersion associated with a characteristic. Quantifies the variation in measurements.
variantPhenotype that is different from the wild type or standard.
variationDifference among individuals in a population.
variegationIrregularity in pigmentation of plant or animal tissues due to variations in phenotype of different sectors of the tissue.
vas deferensPaired ducts that carry sperm from the paired epididymides to the urethra of the penis. It is enlarged (ampulla) near the junction in the urethra.
vectorSelf-replicating molecule of DNA which can transfer a segment of DNA between host cells.
vegetative reproductionAsexual reproduction. Many common flowers, for example are reproduced in the nurseries and at home by sprouting cuttings from a plant without seed formation.
veneral diseaseDisease spread by sexual intercourse.
ventrallower side of an organism with bilateral symmetry.
wild typeStandard phenotype of an organism.
wobble theoryTheory explaining how one transfer RNA molecule may recognize two different codons; the first two bases in messenger RNA pair according to base pairing rules, but the third has leeway (wobble) that allows it to pair with a variety of bases.
x chromosomesex chromosome; in humans, fruit flies, and certain other organisms, females have two X chromosomes and males only have one.
y chromosomemale sex chromosome in humans, fruit flies, and certain other organisms.
zona pellucidaCovering around the oocyte or egg that protects it and is a block to polyspermy.
zygoteCell produced by the union of gametes.
zygotene stageStage in meiotic prophase in which homologous chromosomes pair up, and visible bodies in the nucleus are now bivalents.