Chestnuts carrying Agouti (bay) gene

[Santi]

Hi,
Is there any way to tell if a chestnut carries the bay gene from his parent's colours?

I hope this isnt too long winded but if...

Chestnut 1

has parents

sire=Black + unknown colour mare

but her parents are

sire=Chestnut dam=Bay


Am i right in thinking the Black horse must be Eeaa to be able to sire a chestnut?

And the unknown colour mare must be ...Aa or ...AA?

So the Chestnut 1... can he be a eeaa, or does he have to be eeAa or eeAA?

Chestnut 1 is the sire of my chestnut mare.
I am trying to see if i can work out the probability of her having a bay foal from a black EEaa stallion.

I found a great colour chart that gives all the possibilities of different colour matings - i felt much clearer after a look at this!

http://www.vgl.ucdavis.edu/service/horse/coatcolortable.html


This forum is great !

Caroline.

[Kalypso]

Ok, I'm going to attempt this explanation...chev will likely come along and correct any mistakes ;)

I worked this all out on paper 'cause I was bored, but may have gotten some bit wrong, knowing me :D

You ARE right in assuming the black sire of Chestnut 1 must be Eeaa because He must have an 'e' to pass on and must have two recessive 'a' or else he would be bay, not black.

Now, your chestnut and bay parents (the first generation) to get your mystery mare: the chestnut sire must be ee but could be aa, Aa or AA because it doesn't matter what form of the agouti gene he has as he won't show it. The bay damn must be Ee or EE and Aa or AA...meaning the mystery mare can be Ee or ee and Aa, AA, or aa

meaning...your Chestnut 1 can be aa or Aa, but cannot be AA because the black sire cannot have any 'A' to pass on, he could only have gotten one 'A'. he must also, as I'm sure you know, be ee. So he can be eeaa or eeAa

Geee...I hope that made a bit of sense?

I'm not sure about the breeding of your mare, though, because you only gave the information for her sire? Her sire is either eeaa or eeAa, based on his parents and THEIR parents...but I've no idea what her dam is...your mare is obviously ee, but I can't be sure if she is aa, Aa, or AA because don't know which of the agouti genes her dam had. Was her dam chestnut, bay, or black?

so, guessing...if your mare is mated with an aa stallion: If your mare is aa there would never be a bay; Aa there would be a 50% chance of a bay foal; and AA there is a 100% bay foal rate.

It's late, though, and chances are I mixed something up...now I keep going back over it and second guessing what I did...hehe...Chev, help! :D

[chev]

Am i right in thinking the Black horse must be Eeaa to be able to sire a chestnut?

Yes. :)

And the unknown colour mare must be ...Aa or ...AA?

Not neccessarily. Unknown mare has thrown one chestnut foal, so we know she has at least e. Unfortunately, without knowing if either of her parents are homozygous for bay there is no way to say what other genes she carries. Either or both of her parents could be AA - in which case unknown mare will have at least one A; but it could also be the case that the chestnut parent is aa and the bay parent Aa and neither passed on bay, which means she'll only ever throw bay if the sire passes on both bay and black.

There is a test for Agouti; in this case, that is the only clear way to say whether or not she carries it. Umless, obviously, she throws a bay foal to a black stallion!

The only time you can honestly say whether or not a chestnut carries agouti by looking at the colour of the parents with any real certainty is in the case of a chestnut born to two blacks; where it's plain that neither parent had agouti to pass on. :)