Читать книгу Horse Genetics - Ernest Bailey - Страница 66

When a gene at a particular “locus” (the position of a gene on a chromosome) has two alternative forms (variants) we call these “alleles.” For example, the Extension locus has two alleles, one for black hair (E) and one for red hair (e). We have learned the underlying molecular mechanism is a result of variation at the gene MC1R (Marklund et al., 1996). This gene was used as an example in the preceding chapter and is discussed further in Chapter 7.

Gray is another gene which influences coat color. The Gray locus has two alleles, G for gray and g for non-gray. The Gray locus is different from the Extension locus and is caused by a variation in an entirely different gene (discussed in Chapter 12). The allele responsible for gray is not allelic to the colors red or black. It comes from a different locus with a different gene action. Gray is an entirely different property of hair color. However, Gray (G) is an allele for non-Gray (g) at the Gray locus. Black (E) and red (e) are alleles of each other at the Extension locus.