Excited... and Nervous... - Page 3 - The Horse Forum

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post #21 of 27 Old 08-02-2013, 10:10 AM Thread Starter
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Oakley's results are back. E/e, A/A, N/To. Nothing else, color wise, so very boring results. But it does tell me that if her foal is born sorrel, then it will be heterozygous for tobiano and if the foal is bay/brown then it will be homozygous for tobiano.

She's negative for everything on the disease panel, though, and that's way more important!
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post #22 of 27 Old 08-02-2013, 10:18 AM
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Quote:
Originally Posted by JetdecksComet View Post
Oakley's results are back. E/e, A/A, N/To. Nothing else, color wise, so very boring results. But it does tell me that if her foal is born sorrel, then it will be heterozygous for tobiano and if the foal is bay/brown then it will be homozygous for tobiano.

She's negative for everything on the disease panel, though, and that's way more important!
Just to clarify for the casual reader, how do you know her tobiano is linked to the black and not the red?
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post #23 of 27 Old 08-02-2013, 01:35 PM Thread Starter
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Her sire was a brown homozygous tobiano and her dam was a solid chestnut. :)

I didn't give color info on the sire and dam beforehand because it would have made guessing too easy. I wanted opinions based on phenotype alone.

Now I know she's can't produce a black foal, so my only chances are a red heterozygous tobiano foal or a bay/brown homozygous tobiano foal.

Last edited by JetdecksComet; 08-02-2013 at 01:38 PM.
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post #24 of 27 Old 08-02-2013, 01:39 PM
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So the tobiano is linked to the E/e gene?

Celeste
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post #25 of 27 Old 08-02-2013, 02:08 PM Thread Starter
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Yes, tobiano is linked to extension (the E/e here) and roan. We don't worry about roan in this scenario, because none of the horses involved are roan (but interesting to note... because of this linkage, you can't have a homozygous tobiano that is roan or a homozygous roan that is tobiano. So, if you see a roan tobiano, you automatically know it's heterozygous for both roan and tobiano.)

Because I know my mare's tobiano came from her brown sire, I know that her tobiano gene is linked to her black gene and not her red gene.

It's very, very rare for tobiano to break linkage and "crossover". It could happen, but is very unlikely. If you want to read more about it:

Tobiano Spotting (Near the bottom see "Understanding Tobiano Genetics.")
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post #26 of 27 Old 08-02-2013, 09:04 PM
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Originally Posted by JetdecksComet View Post
Yes, tobiano is linked to extension (the E/e here) and roan. We don't worry about roan in this scenario, because none of the horses involved are roan (but interesting to note... because of this linkage, you can't have a homozygous tobiano that is roan or a homozygous roan that is tobiano. So, if you see a roan tobiano, you automatically know it's heterozygous for both roan and tobiano.)

Because I know my mare's tobiano came from her brown sire, I know that her tobiano gene is linked to her black gene and not her red gene.

It's very, very rare for tobiano to break linkage and "crossover". It could happen, but is very unlikely. If you want to read more about it:

Tobiano Spotting (Near the bottom see "Understanding Tobiano Genetics.")
Just to further clarify for those playing at home. The chance of it "swpping" linkage is approximately 7%.

Tobiano is "linked" to extension, which means that it is passed down only with that copy of the extension gene. So in this case, we can be fairly certain that the mare has her tobiano linked to a dominant extension gene, so whenever she passes that E to her foals, she will always pass on a To gene. The same thing happens with roan, which is a different mutation on the same locus as tobiano, so, as JDC said, you can't have a horse that is homozygous for tobiano and has roan as well.

Interestingly, dominant white and the only testable sabino are on the same locus as tobiano and roan too - I haven't seen any research that indicates they are extension linked, but I wouldn't be surprised if they are too.

Mods, grant me the serenity to see the opinions I cannot change, courage to change the ones that should change, and the wisdom to spot the trolls.
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post #27 of 27 Old 08-05-2013, 11:46 PM Thread Starter
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Nova's came back today. E/e a/a To/To, n/n everything else. Yes, everything. None of the current splash, no frame. So, another unexplained blue-eyed horse.

Negative for all the genetic diseases, too! Yay!
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