colorgenotypediscussion5

WHAT MAKES BAY & CHESTNUT (A)

What Makes Bay & Chestnut (A)

Possible Color Genotypes

Possible Color Genotypes/Black & Black-to-Grey

Possible Color Genotypes/Bay & Bay-to-Grey

Possible Color Genotypes/Chestnut & Chestnut-to-Grey

Sample Matings

Glossary of Terms Conclusion

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BAY

The DNA test for the presence of the A allele is called the AGOUTI Test. This test has been in use for a relatively short time. [Before this test, some horses that were tested and considered homozygous for black, produced chestnut--this is now explained to be caused by a rare allele at a different locus and named the "Black Forest" gene.] The presence of the dominant A allele will restrict the black hair produced by the dominant E allele to the points (mane/tail, ears, knees and hocks, lower leg areas), making the horse a bay.

Therefore, a bay must have at least one dominant A allele and one dominant E allele. (Most horses, including Arabians, have TWO dominant A alleles.) A black-bay horse will have some reddish/brownish hair around the muzzle even though its body might look totally black.

CHESTNUT

If no dominant E allele is present, the horse will be chestnut. [Without additional information either by parentage or DNA testing, it is impossible to know for certain whether a chestnut horse possesses dominant A allele(s) or recessive a allele(s).] Chestnut horses have manes/tails that are flaxen (lighter), darker (but not black), or the same color as its body hair.

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Special Note: The recessive a allele is rare. Since a black horse must have two recessive a alleles, this is the reason that black is a rare color and the bay and chestnut colors are so common.

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Introduction

The Basics

What Makes Grey (G)