Homozygous Roan Lethal?

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Homozygous Roan Lethal?

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    08-20-2012, 09:10 PM
Homozygous Roan Lethal?

So I'm currently taking a genetics class. First day was today and she put up some extra credit already for us to do. Lucky for me it's all about horse genetics YAY! I might need more help when I start into it more. She gives us pictures and we're suppose to say what it's full genetic coding is...

Anyway...I'm reading the powerpoint and according to it: "All roan horses are heterozygous Rnrn as homozygous RnRn is lethal".

Is this true? I've actually never heard of this. Does it work the same way as lethal white? If I thought about it correctly this would mean breeding two roans would have a 25% chance of lethal. Am I totally crazy or is this incorrect?
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    08-20-2012, 09:15 PM
I've never heard of such a thing in roans...
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    08-20-2012, 09:20 PM
Yeah that's why I'm asking. I pretty much did this when I read it:


I need some of the other color smarties so that if this is indeed incorrect (like I feel that it is) I can go to my professor and be like "Y .U NO TEACH RIGHT?!"
    08-20-2012, 09:21 PM
Roan used to be thought of as embryonic lethal, but for the type of roan that is testable now that has been proven wrong.

This stud is homozygous for roan -


And this is from the UC Davis page - Roan

Roan is a white patterning coat color trait of intermixed white and colored hairs in the body while the head, lower legs, mane and tail remain colored. Roan horses are born with the pattern, though it may not be obvious until the foal coat is shed. The white and colored hairs are evenly mixed in horses that inherit the classic Roan gene, which can differentiate this from several mimic patterns called roaning. Roaning patterns tend to be uneven in the distribution of white hairs and the inheritance of roaning has not been defined. The Roan gene is found in a variety of breeds such as Quarter Horse, Paints, Peruvian Paso, Paso Fino, Welsh Pony, Miniature and Belgian, but not in Thoroughbreds or Arabians.

Although it has been suggested that Roan is a homozygous lethal, evidence from the Quarter Horse breed indicates otherwise. Production records have documented the existence of Roan Quarter Horses that produce 100% Roan foals. DNA tests have confirmed homozygosity in the genomic region that contains the Roan gene.
    08-20-2012, 09:28 PM
Hm...excellent. So would it be worth sending that article to my professor?
    08-20-2012, 10:21 PM
Some professor...just reinforces my lack of respect for academia. Years and years ago, people used to think a "double roan" was lethal, just like a "double white" as they used to call them. It was an old wives tale that I haven't heard come up in 30 or 40 years...as many roans as are crossed with each other you would think that belief would have fizzled out long ago. I suspect your professor got it mixed up with lethal white...

Yes, you should tell her...and give her a homework assignment...
smrobs and Evansk like this.
    08-20-2012, 10:36 PM
From what I understand it is 97% lethal. Sometimes some lucky horse is strong enough to be born Homozygous but its very rare. There is one line though I cannot remember what line it is that throws a lot of Homozygous roans. Though I could be totoally wrong. That's just what I've read.
    08-20-2012, 10:36 PM
I would pass that information along to her.

You wouldn't believe how many times I wanted to drive to where Po was taking her color classes and smack the teacher in the back of the head...
smrobs and Poseidon like this.
    08-20-2012, 10:37 PM
TB, if possible, please do share with us that information if you can find where you read it.
    08-20-2012, 10:46 PM
Originally Posted by NdAppy    
I would pass that information along to her.

You wouldn't believe how many times I wanted to drive to where Po was taking her color classes and smack the teacher in the back of the head...
Yes, please send it to her.

My professor hated me during the color section of my class last year because of my constant corrections (ie, "White." There are quite a few ways to get an entirely white horse, not "greys have dark skin, whites have pink skin." GAH!). I sat texting NdAppy furiously under my desk because everything was so wrong.
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