What chance do I have that my mare is homozygous? - The Horse Forum
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post #1 of 9 Old 07-13-2008, 07:41 PM Thread Starter
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What chance do I have that my mare is homozygous?

The paint mare I plan to breed next season has some markings that I was told once point towards her being possibly homozygous for spots.

She is basically solid with a white face, shorts white socks, and two belly spots. One belly spot is very solid and clear. The other is misty looking.

The outline of her white face slowly fades out on the edges, giving a misty "outline" around her facial marking. Someone told me this points towards homozygous tendencies. Also, she has two nickel sized chesnut spots in the middle of her white face. Someone said these are called "ink spots" and also point towards being homozygous.

Are any of these statements true, and is the misty (rather than solid) spot on her belly another indicator of being homozygous? I don't want to go through getting her tested. If her baby has no color I will still love it. I just wondered. Also, someone said homozygous paints with those indicators are homozygous for the tobiano color pattern, rather than just spots in general. What do you think of this statement?

I'll take a picture of her face and belly spot and add it tomorrow.
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post #2 of 9 Old 07-13-2008, 07:55 PM
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A picture would be good, but ink spots indicating homozygous is true, BUT horses can have ink spots and not be homozygous also.

My stallion, Dez, has these "ink spots/puppy paws", but cannot be homozygous. He cannot be homozygous because his sire is overo, his dam tobiano.

The only way to produce homozygous tobiano is to have tobiano x tobiano or sometimes tovero x tobiano. Homozygous is associated with tobiano...homozygous overo = lethal white = foal death.

I would either pull the hairs and pay the $65 to have her tested, or breed her to a homozygous stallion to ensure color. I know you don't care about color, and will love the foal either way, but color is so cool, and on an APHA, is pretty important. If for any reason you ever have to sell - it is an important selling point.

- look closely at this photo, do you see the spots within the white (esp. on his neck). Those are the sort of spots you look for, but esp. look for spots you can see a black base around.
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post #3 of 9 Old 07-13-2008, 08:17 PM Thread Starter
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Well, she is an overo. She has no white over her back (belly spots only). The one solid spot is more irregular and splashy than round. She has a solid colored tail, one blue eye (which I read was more common in overo coloring), and the white on her legs are very low, not extending above the knees.

So does this mean she has no chance of being homozygous, because she is not a tobiano? I still am making payments on her, so I don't yet have the papers in my hand, and can't remember the color pattern of her sire/dam. If her sire/dam were both tobiano and she turned out overo, could she still be homozygous? Is it even possible to produce an overo out of two tobianos?

Also, I read that if you have an overo that carriers a lethal white gene (as you said a homozygous overo would), you need the other parent to also be a carrier for an actual lethal white to occur. The stud I want to use is a tobiano. The article also said tobianos can very very rarely carry a lethal white gene. If she did carry lethal white, breeding her to a tobiano would effectively keep her from producing lethal white correct?

I've always had it in my mind from breeders and trainers that it is never a good idea to cross over x overo as the chance for LWS is much too great.
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post #4 of 9 Old 07-13-2008, 09:20 PM
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I believe...

You cannot have a homozygous if she is overo because homozygous overos show in the form of lethal white, and always die.

Breeding her to a tobiano will lessen your chance of lethal white, but I think you are correct that there is a slim chance of a tobiano carrying lethal white.

Breeding your colored mare to a colored stallion does give you about 75% odds of getting a colored foal (25% tovero, 25%tobiano, 25%overo, 25% solid).

I don't think breeding 2 tobianos would leave the possibility of an overo.

There are various kinds of overo, and would be important for you to know which your mare is. Frame, I believe is the kind that carries lethal white. Splash is another kind...

There is a lot about color genetics that I still do not know, so I could be a little wrong....I am just repeating to you what I have read or been told by those who know better than me.
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post #5 of 9 Old 07-15-2008, 02:15 PM
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If she is a frame overo never breed to another frame overo. The ink spots thing is true, but only for tobianos, as overos can't be homozygous.

"Research indicates that, when bred together, splash whites have never produced a lethal white and sabinos have produced few--if any--lethal white foals."
Supermane is offline  
post #6 of 9 Old 07-15-2008, 04:18 PM
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Try this genetics calculator

On the sixth day, God created the Quarter Horse.
On the seventh day, he Painted the good ones.
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post #7 of 9 Old 07-17-2008, 10:43 PM
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If she's overo she may also carry the tobiano pattern. A pain can only be homozygous for tobiano, no other pattern. So if she is, she's technically a tovero. Toveros don't always have the ink spots (although this one does) and stuff. For example...the stallion below is homozygous for tobiano but as you see he looks overo. He's a tovero and the only way the owner knew this was to have him tested.
palogal is offline  
post #8 of 9 Old 07-23-2008, 01:12 PM
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Do you know what her registered name is? If so, I can look her up on the APHA website for you.
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post #9 of 9 Old 08-04-2008, 07:10 PM
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Sabinos can also have markings like that. I know a lot of sabinos, and most of them have a faint outline too. Some even have some roaning (not true roan, just rabicano gene).
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