Horse genetics, round 2 ding ding ding

[Ryan Wunsch]

O.K, sorry, couldn't help it.

I'm hopefull to get a good answer regarding the overo / lethal white being linked theory.

I emailed 3 different people who should have the newest information.

www.vgl.ucdavis.edu/contacts.html
Did a lot of the research for genetic mapping of horses

www.horsetesting.com/contactus.htm
these people do genetic testing for lethal white and tobiano

128.101.246.19/mvb/faculty/mickelson.htm
Dr. Mickelson is the man who is in charge of the lethal white research project that got the funding in those links i had posted in the thread under the horse discussion

I will post the replies I get them as soon as I get them, no matter what the answer is. I am very curious to know if they've made any ground on proving a link between frame overo and lethal white in horses.

Here is the letter I sent to Dr. Mickelson, and is the same as I sent to the other 2 sources.
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Hello Dr. Mickelson

I am the president of HISS, the Herpetology Information Society of Saskatchewan. Recently myself and 2 students from the University of Saskatchewan (HISS members) were having a discussion about horse genetics, and lethal white (I believe there are some lethal white issues with some of the color genetics in snakes)

Anyways, I also keep horses (paints and dilute quarterhorses), and have been learning about color and coat genetics. We were discussing the link of Lethal White to Frame Overo. I am under the understanding from a few resources that I have read, that there was a recent theory that lethal white was not linked to Frame Overo horses, and that a copy of the recessive Lethal White gene could be passed to a horse that was not genetically Frame Overo. These resources were internet based, and likely second hand information which I realize is not the best source, hence this email to you.

I'm emailing you to find out what newest theory on the subject is. Is it like above, or is it thought that the solid looking horses, tobianos and other patterns that carry Lethal white, are actually minimally marked Frame Overos.

I know that tobiano can be tested for. Are there any plans to test for the other paint patterns, specifically Frame Overo. My thoughts are that without a test for Frame Overo, It would be impossible to prove that Non Frame Overo horses can carry the lethal white gene, and that the 2 aren't linked, or to prove that they are in fact linked.

Also, is the current theory that all Frame Overo horses carry the Lethal White gene?

A few of us are really looking forward to a reply, Thank you in advance for any help you can offer us.

Ryan Wunsch

www.hisscanada.com

[kaley]

What no hot bikini girls!? I'm disappointed!

Seriously though, it looks like a good letter, and I eagerly await the reply!

Kaley

[Ryan Wunsch]

Got a reply from Dr. Mickelson. Looks like I was right

Frame Overo is lethal in homozygous form. Sounds like there isn't a seperate gene that is linked to Frame Overo, it is the gene, and is lethal in homozygous form.

He sent me the 17 page study, I'm sending it to you Kaley, anyone interested in reading it either post here or email me and I'll send you a copy.

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Ryan,

I will briefly summarize some work we published several years ago in Santschi EM, Vrotsos PD, Purdy AK, and Mickelson JR. (2001); Incidence of the lethal white foal endothelin receptor B mutation in white patterned horses: evidence for genetic heterogeneity in the overo coat pattern. Am J Vet Res 62, 97-103.

The LW gene is in fact the frame overo gene; aka an allele of the EDNRB gene A single copy (heterozygous) for this gene almost always results in the horse having a frame overo character. Receiving a copy of the mutant EDNRB gene from both parents results in a foal being all white and dieing from LW foal syndrome. However, the frame overo gene in its heterozygous state is influenced by other genes, and this can lead to confusion.

Several percent of horses that carry the LW gene are very minimally marked frame overos or may not be classified as overos at all. This while they can produce LW foals if mated to another carrier. So, the color pattern produced by a single copy of the LW gene is mostly frame overo, but this may be masked or influenced by other genes such that you get lots of white or almost none. There are even carriers of the gene that are over 99% totally white, but not lethal whites.

By testing for the LW gene you are testing for the frame overo gene. But again, realize this is only one of the genes that can give rise to white patterning.

Hope this helps.

[jscarrlay]

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