HGG Community Forums

Here are a few more
http://hj2.huntandjump.com/horse.php?horseid=183905
http://hj2.huntandjump.com/horse.php?horseid=183907
http://hj2.huntandjump.com/horse.php?horseid=183909
http://hj2.huntandjump.com/horse.php?horseid=183910
http://hj2.huntandjump.com/horse.php?horseid=183911
http://hj2.huntandjump.com/horse.php?horseid=183912

It takes two genes for a horse be a bay. They need black, the dominant form of the Extension gene (the first one on the gene test). Then they need to have the dominant form of agouti, which pushes the black to the mane, tail, and lower legs.

Chestnut horses can carry dominant agouti, which all those chestnuts do, but they are homozygous for red, which is the recessive form of the Extension gene, so they have no black to push around in their own coats or to pass on to their foals.

If you breed your homozygous bay chestnuts to blacks, you may get bays, because they will pass on one dominant agouti. If the mate is EE, then the foal will definitely be bay. If it is Ee, then you could get either a bay or a chestnut. If you breed them to bays, the foals may or may not be bay, depending on whether their mate passes on a black E or a red e. If the latter happens, then the foal will be chestnut.

Don't put yourself down. It is a very complex study that hasn't even been completed, though quite a few of the most common genes have been found and their effects identified. Or perhaps I should phrase it the genes producing some of the most common color effects have been identified.

And I think that I was a bit surprised the first time I created a homozygous bay horse and got a chestnut, until I thought about it carefully.