Back to genetics again...

[sandy]

Boy, the more I study it the more confused I get! LOL! I had emailed the Animal Genetics lab in Fla. and commented favorably on their foal calculator, and I asked a simple question on genetics. The person who responded to me, Rolf, was super nice and helpful and asked if I had any more questions. So, I sent him a few more and promised I wouldn't bother him again. But he answered those questions and said to keep them coming! Boy, I've hit a gold mine!

But I really don't want to drive him nuts, so I thought I'd put out a question to our color experts here.

Let's say you have a black and white tobiano stallion, and he's homozygous for tobiano. You breed him to a solid chesnut non-tobiano mare.

If he's homozygous for tobiano, as I understand it you will ALWAYS get a tobiano. (even if minimally expressed).

Now, since black is a dominant gene and red is recessive, would the foal also always be black "IF" the mare is not homozygous for red?

Also... can a horse actually be a chesnut color and NOT be at least heterozygous for red?

I sure wish I'd paid more attention to those biology classes in college.

sandy

[beckys]

I'll jump in and try to answer!

Your black and white homozygous tobiano stallion bred to a solid 'red' mare will give you:
A tobiano foal even if minimally marked.
A foal that could be black or red. What you didn't mention is whether the stallion is homozygous or heterozygous for black too. If he's homozygous for black and the mare doesn't carry agouti, then the foal will be black. If the stallion is heterozygous for black, then the foal will be black, red or bay (if the dam also carries agouti)

A horse cannot be red unless it is homozygous for that color. A red horse will always pass along a red gene. Two red horses will ALWAYS produce red. A genetic law.

Having said that, a red horse can carry other modifiers such as agouti or silver and it not be expressed. So you can get some suprise foal colors if you're not aware of what the sire and dam carry.

[sandy]

Thanks for helping out, Becky! No, I forgot to say if he were homozygous or heterozygous for black. I didn't because perhaps I'm still confused about something. I thought that black was always dominant over red, so if the mare were NOT homozygous or heterozygous for red, I assumed the black stallion would produce a black foal (since I thought black was dominant.)

But now I understand that he would have to be homozygous for black in order to produce a black foal. Otherwise, he would only produce one 50% of the time, I think.

Now, if the stallion were homozygous for black and the mare were homozygous for red, but carried no agouti, is THAT when the black becomes dominant, or will there still be a 50% chance the foal would go either color?

I'm really getting into these genetics. But just when I think I am starting to understand it a bit, I realize I don't.

sandy

[beckys]

If the stallion is homozygous for black and the red mare carries no agouti, then the foal would be black. Black is dominant to red, so yes, black would be the color of the resulting foal.

There's so much to learn regarding color and it's so fascinating! Having the color and pattern tests that we now have, help tremendously!

[Marion]

My stallion has produced red, black and silver depending on the color of the mare his is bred too.
So far with one black bay mare his has produced two chestnut pintos, with my black mare he has produce a black and white pinto, and with my bay mare he produce a bay. Also with my red mares he has produced red colts. My silver dapple mare he produced a silver pinto.