Basic laws governing biological inheritance in dogs were discovered in the 1860s by Gregor Mendel, the Austrian monk who gave his name to the principles which hold good to this day, though our understanding of the underlying mechanisms has altered. A particular gene controlling a specific function is always found at a particular point or locus on a certain chromosome. As the chromosomes come in pairs there can only be two of any particular gene in an animal, one on the chromosome from the sire and one from the dam. The gene at a locus may control a specific function, but differing versions (alleles) of the gene may influence this function. If a dog carries two identical alleles it is said to be homozygous at that locus; with two different alleles it is heterozygous. Some alleles are relatively powerful (dominant) and can influence the outward expression of a feature even when present on only one chromosome; others must be present on both chromosomes (recessive) to have any effect. In the science of genetics letters are used to distinguish genes, capitals indicating dominant genes and lower case recessive versions.
Many characteristics, particularly coat color, are inherited in a relatively simple fashion, others are more complex. Some genes act in apparent isolation, while others are influenced by the presence or absence of genes at some other locus. The B/ b series which determines black and chocolate coat color is influenced by the so-called extension series of which two versions, E and e, exist in the Labrador Retriever breed. The dominant E allows black pigment to form over the whole body, assuming the animal carries black, but the recessive allele e prevents it and causes pigment to be tan or yellow except on the nose and pads. Therefore, in order to be black, a dog requires not only the B allele but also at least one E allele. A BB dog which also carried EEwould have yellow coat color because the B series cannot function in EE presence of the the combination.
Many characteristics, particularly coat color, are inherited in a relatively simple fashion, others are more complex. Some genes act in apparent isolation, while others are influenced by the presence or absence of genes at some other locus. The B/ b series which determines black and chocolate coat color is influenced by the so-called extension series of which two versions, E and e, exist in the Labrador Retriever breed. The dominant E allows black pigment to form over the whole body, assuming the animal carries black, but the recessive allele e prevents it and causes pigment to be tan or yellow except on the nose and pads. Therefore, in order to be black, a dog requires not only the B allele but also at least one E allele. A BB dog which also carried EEwould have yellow coat color because the B series cannot function in EE presence of the the combination.
