Heterozgous tobiano - The Horse Forum
 
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post #1 of 8 Old 08-14-2012, 11:37 AM Thread Starter
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Heterozgous tobiano

Hi,
probably a pretfy simple to answer question for you guys - I came across a horse for sale ad the other day that had the picture of a solid bay horse, and stated that the mare had been tested heterozygous tobiano. I always thought that tobiano was expressed even if it's heterozygous, hence a homkzygous tobiano throws only tobiano foals... is that not true?
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post #2 of 8 Old 08-14-2012, 12:04 PM
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Horses with white patterns are not always obvious; however, tobiano almost always expresses itself. There was a mare posted not long ago that was of the most minimally marked tobianos I've seen.

Could you link the ad?

And yes, a homozygous tobiano will always pass on the tobiano gene whereas heterozygous will pass it on 50-50.
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post #3 of 8 Old 08-14-2012, 02:23 PM
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Agreed. If it is homozygous, the gene will pass on, but if it is heterozygous it is not a guarentee.

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post #4 of 8 Old 08-15-2012, 07:12 AM Thread Starter
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Here's the link:

Broke to ride - APHA mare in foal to CBHI Stallion - Alberta Livestock For Sale - Kijiji Alberta

So would the face and leg markings be enough to be considered minimal expression of the tobiano?

On another note, that means solid, APHA registered Paints mostly have one or more overo genes, right? (since tobiano would be expressed most of the time)
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post #5 of 8 Old 08-15-2012, 11:43 AM
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Quote:
Originally Posted by Regula View Post
Here's the link:

Broke to ride - APHA mare in foal to CBHI Stallion - Alberta Livestock For Sale - Kijiji Alberta

So would the face and leg markings be enough to be considered minimal expression of the tobiano?

On another note, that means solid, APHA registered Paints mostly have one or more overo genes, right? (since tobiano would be expressed most of the time)
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She doesn't look it to me, and I would never peg her for tobiano if it weren't for the DNA testing; most of the time minimal tobianos at least have a bit of white in their tails. But of course, genetics don't always follow the "rules"

Many of the SPB registered horses do carry some type of overo (which hides more frequently), but some of them also carry no pinto genes at all and are the product of heterozygous parents who didn't pass along the gene.
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post #6 of 8 Old 08-15-2012, 02:43 PM
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Possibly she might. I'd ask to see the copy of the test results if I were really interested. However, she's most likely got frame and splash going on too. Tobiano doesn't put white on the face like that.

And yes, many horses registered SBP actually do have a white pattern. Mine has frame and is registered BS. Some are actually just solid though. For the APHA, phenotype is far more important that genotype.
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post #7 of 8 Old 08-16-2012, 01:11 AM
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Homozygous tobiano (tested)



Heterozygous tobiano (tested)



Another tested Homozygous tobiano mare



Tobiano can be very minimal and yet still be there. I have yet to see a horse test positive for tobiano and have no white on them at all, usually they will have at least a heel spot on a back foot from what I have seen/heard about. However, with the attitude that "normal" leg and face white isn't related to white marking genes, there may be "solid" horses that have tobiano and just aren't tested for it as the owners don't realise that it could still be there.

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post #8 of 8 Old 08-16-2012, 01:29 AM
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Yep, that's the funny thing about white pattern genes. Just because they carry them doesn't guarantee that they will express them.

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