Punnet Square for Coat Color
Let's take a look at how some of the genes that control pigment formation in dogs fit into the inheritance patterns that we learned back in the advanced concepts section. For example, let's mate two dihybrid (BbEe) Laborador Retrievers. We know that these individuals will be black, because the B- genotype makes dark eumelanin pigment, and because the E- genotype produces functional MSH receptor, which stimulates eumelanin production in the first place.
If we look at the offspring of this mating, we can see that 9/16 will be B-E-. These individuals will be black for the reasons stated above. Another 3/16 of the progeny will be bbE-. These individuals will be chocolate because their E allele produces a functional MSH receptor, while their bb genotype interrupts eumelanin synthesis and produces a brown pigment. Finally, 4/16 of the progeny will be unable to make a functional MSH receptor (due to their ee genotype) and thus will have yellow coats.
As an item of further interest, because the MSH mutation does not affect pigmentation in all areas of the body, B-ee dogs will have yellow coats and black noses, while bbee dogs will have light noses.
Many phenotypes are the result of a well-orchestrated series of biochemical events and cell activities. The orchestration of these activities and events are through the genes that control the trait. If you want to learn more about the inheritance of coat color in dogs or cats or horses, you should consider enrolling in one of the distance-education courses available from Cornell University. More information about these courses can be found in the next section of this web site.