Help me with the genetics of Black in TBs

[springboro]

I used to know this, but am being lazy and not looking it up.

There is a sabino chestnut mare being sold, and her 1/2 sister is a true black. Apparently also her dam, but I can't confirm that.

Does a chestnut horse have the ability to "carry" the black gene. My guess is not as I have always heard that chestnuts are all recessive to start with, and that if another gene were present it would be expressed.

How'd I do at color genetics 101??

[Jorge]

There is a very interesting thread at:

http://www.search.com/reference/Equine_ ... r_genetics

[Nessa]

Chestnuts only have the red gene, so they can only pass on the red gene. Blacks and bays can have both the red and black genes at the same time (though physically they show only black or bay) and can pass on either one or the other to their offspring.

[xfactor fan]

There are two sets of genes involved. Base coat color, either red or black. Red is recessive to black in gene geek speak E (black) e (red) A black horse is either EE, two copies of the black base coat, or Ee one red, and one black.

The bay color is a modifier the only works on horses expressing the black based and Agouti--the correct name for the bay color pushes the black coat color of the horse to the outside edges of the horse, giving the impression of a red horse with black points.

There seem to be four variations of Agouti: Bay, Wild Bay, Brown and Black. Regular Bay is A, black is a and is recessive to Bay. So a Bay horse could be Aa or AA. For that matter a chestnut could also be AA, or Aa or aa but no one could ever tell because this gene doesn't show up on a red base coat. A black horse would be aa.

So the short answer is yes a black sabino could have a chestnut sibling.

[Sunday Silence]

[quote="springboro"]I used to know this, but am being lazy and not looking it up.

There is a sabino chestnut mare being sold, and her 1/2 sister is a true black. Apparently also her dam, but I can't confirm that.

Does a chestnut horse have the ability to "carry" the black gene. My guess is not as I have always heard that chestnuts are all recessive to start with, and that if another gene were present it would be expressed.

How'd I do at color genetics 101??[/quote]

Who are these horses in question?

[xfactor fan]

Correct, chestnut is recessive to black base coat color. Unless you have the horse tested by a lab, you can't tell which of the Agouti genes a horse carries.

For example a black mare that has a chestnut filly has to be Ee (one black one red gene) and aa two copies of the black version of the Agouti gene.

So the filly has to be ee (both red genes) and one black Agouti gene a? and an unknown agouti from her sire.