In some instances the heterozygote (carrying two different alleles) overrules the homozygote with two identical alleles where dominance is incomplete. A classic example is the colour factor or merle gene found in some Collie breeds. Most dog breeds and indeed most Collies carry the alleles mm and show no trace of blue; however, some Collies are Mm in genetic structure and have the characteristic dappled coat of normal and bluish pigmentation. A dog inheriting the MM state is not merle but nearly all-white; it is also frequently deaf, with related eye defects. Mating merle (Mm) to merle (Mm) is rarely practiced as it may result in MM animals; most merles come from Mm to mm matings in which the genotype MM cannot be produced.
Cynologist
Cynology: Puppies Dogs
February 4th, 2010 by admin