- Basic Concepts
- DNA & RNA
- Simple Inheritance
- Modify Mendelian Ratios
In Mendel's studies, he proposed that there are two alleles for every gene, the dominant of the two having its phenotype expressed in a heterozygote. However, a gene can have more than two allelic forms segregating within a population.
These genes are referred to as having multiple alleles. This does not mean that the gene in a particular individual possesses more than two alleles. An individual can only have a maximum of two of the alleles, one maternal and one paternal, no matter how many alleles exist in the population.
An example of multiple alleles of a gene is the C series in dogs.
C is required for color while cc yields an albino. The genotypes and phenotypes are as follows:
- C is a dog with color series expressed
- cch is a chinchilla patterned dog
- cd is a white dog with dark eyes
- cb is a pale gray dog
- c is an albino dog (pale eyes and nose)
The series works in such a way that C>cch>cd>cb>c. When an allelic series is written like this, it means that the allele to the left, in this case the C allele, is dominant to every allele to its right, while the next allele (cch) is dominant to everything but the allele to its left (C), and so on. In this system, the c allele is recessive to all of the other alleles.