# Double Homozygous?



## Crazy4horses2 (Jul 12, 2017)

I've never heard this term before I know what homozygous is but would really like to know what this is google wasn't much help any help on this would be appreciated


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## Smilie (Oct 4, 2010)

I can only assume the horse is homozygous for two traits
For example could be homozgous for both black and tobiano


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## Crazy4horses2 (Jul 12, 2017)

That's the only thing I could think of but wasn't sure I'm not sure if my mare is a homozygous but her dad QTS Double Chex is Double homozygous and she's almost a spitting image of him


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## JCnGrace (Apr 28, 2013)

@Smilie is right, it usually refers to tobiano + color, like black, cream, dun or roan.


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## Crazy4horses2 (Jul 12, 2017)

Thank you for clearing that up for me


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## Hotrodz4me (Jul 17, 2016)

Yes. Homozygous for two traits. Unless the person using the term is clueless about genetics. I run into that with people discussing genetic mutations in women on a forum I belong to.


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## Crazy4horses2 (Jul 12, 2017)

Yeah I had asked a relative who took equine collage classes and she told me something completely insane she told me that if the horse is a homozygous and both parents are homozygous then that makes the homozygous foal a double I was thinking and how in the world does that work??


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## JCnGrace (Apr 28, 2013)

Crazy4horses2 said:


> Yeah I had asked a relative who took equine collage classes and she told me something completely insane she told me that if the horse is a homozygous and both parents are homozygous then that makes the homozygous foal a double I was thinking and how in the world does that work??


That made me chuckle.


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## KigerQueen (Jun 16, 2013)

though i commented on this and now its gone? yeah homozygus for two traits.


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## MerriBelle1 (Apr 19, 2017)

I researched this horse and some of its' offspring. It appears they have two (double) alleles on each chromosome. EE is for black and TOTO (or TT) is for Tobiano. So a homozygous black(EE) tobiano (TT) X EE TT will produce 100% Black Tobiano foals. If EE TT is bred to a red or bay tobiano (who is a non silver carrier )and is a AA (Homozygous Agouti) (such as a bay) will produce 100% bay tobiano. It seems like it is really confusing, but read up on genetics and read and read. Eventually it will make sense. Basically this horse as 2 alleles on the black and 2 alleles on the tobiano genes. Very simply this stallion has a high chance of throwing color. Horses can have just one allele on each chromosome and that could change the color. I hope this helps.


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## Hotrodz4me (Jul 17, 2016)

QTS Double Chex has a sorrel dam. He can't be homozygous for black. Both sire and dam are tobiano and they do list him as homozygous for that. I'd want to see test results. He would be Ee for black and could either be TT or Tt depending on who passed what and their status. It is likely since they list him homozygous they have tested for TT and that is what they are refering to. I did not find anywhere they say he is double homozygous but it does list under his sire something about a double color guarantee..


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## Hotrodz4me (Jul 17, 2016)

Well now that I read my above it is confusing. All horses have two alleles for each gene as they inherit one from each parent. Paired alleles (one on each of two paired chromosomes) that are the same are called homozygous, and those that are different are called heterozygous. Black is dominant so even if the horse has only one black allele it will be black. It could be **** or hetero. A sorrel horse will always be homozygous (ee) as that is the recessive and it will only show if homozygous. The sire of QTS Double Chex could be either EE or Ee but his dam is ee. That makes QTS Double Chex Ee, heterozygous for black. His sire Q T Poco Streke is likely TT but the dam is Tt as her dam does not carry tobiano. That means QTS Double Chex could be either TT or Tt and why I said I would want to see the test results.


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## Crazy4horses2 (Jul 12, 2017)

OH That's where it confused me! I seen it when I was trying to find (Dakotas) Dam Thunders Bar Maid I couldn't find any pictures of her but it said something about double homozygous Thunders Bar Maid. I was told that Dakota is homozygous but I don't know if that's true or not either.


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## QtrBel (May 31, 2012)

I couldn't find anything about Thunders Bar Maid except that she shows up in a pedigree for a horse called May Bar Buttons if you google her name. TBM does come up on AllBreed but she is not double homozygous. Her dam is a sorrel with no tobiano. Thunders Bar Maid would be EeTn ( I think they use n for tobiano when it is not present. ) I'd really want to see the test results from the lab if anyone is claiming that she is double homozygous. The daughter listed on Coyote Creek's website, May Bar Buttons, is listed as double homozygous and since TBM is a Black tobiano (EeTn) and the sire is also black tobiano (E?T?) she could well be.

QTS Double Chex is EeTn and Thunders Bar Maid Is EeTn. Phenotypically your Dakota is black with tobiano so could be Ee or EE and either TT or Tn. You would have to test to know for sure.


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## Crazy4horses2 (Jul 12, 2017)

Thank you for that info that was very helpful


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## Crazy4horses2 (Jul 12, 2017)

QtrBel said:


> I couldn't find anything about Thunders Bar Maid except that she shows up in a pedigree for a horse called May Bar Buttons if you google her name. TBM does come up on AllBreed but she is not double homozygous. Her dam is a sorrel with no tobiano. Thunders Bar Maid would be EeTn ( I think they use n for tobiano when it is not present. ) I'd really want to see the test results from the lab if anyone is claiming that she is double homozygous. The daughter listed on Coyote Creek's website, May Bar Buttons, is listed as double homozygous and since TBM is a Black tobiano (EeTn) and the sire is also black tobiano (E?T?) she could well be.
> 
> QTS Double Chex is EeTn and Thunders Bar Maid Is EeTn. Phenotypically your Dakota is black with tobiano so could be Ee or EE and either TT or Tn. You would have to test to know for sure.


Oh I thought I'd add TBM is a Bay Tobiano and her Sire was also a Bay Tobiano. That could be the reason why there are some small brownish looking patches (about the size of my hand if not smaller) on Dakota that I really didn't put any thought into until you mentioned that.


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## QtrBel (May 31, 2012)

That wouldn't change whether she is black or not. The bay would add the agouti gene which restricts black to the points changing the color we label her from black to bay as bay is a modified form of black. While it is possible she is AA as A can hide on sorrel which is her dam's color (there is no black to modify or restrict) more than likely TBM is Aa and only had a 50% chance of passing it. Agouti is dominant to black so if he had it he would be bay and you would see it more clearly. From his pic I think he is black with some fading from the sun and TBM would be EeAaTn. Phenotypically a black horse is always E?aa. Blacks fade and that would show as brownish spots. Do you have any other pics of him? He's a pretty boy. The other possibility is seal brown which if TBM did pass the A gene would be the darkest expression possible of bay and could make him look black at times. The difference in expression would be that they can look black but on the winter coat he would have an orangy or cinnamon muzzle and his soft spots would be that same orangy cinnamon. Does he show that on his winter coat? On Horse Forum they refer to that as BadAs*Brown. Fade from the sun or salt streaking causes it to be higher up on the barrel and face or as a friend says all the peaks and valleys get lightened. Fade is typically more tan or brown and not so much cinnamon. There are two threads you can go to to see more about Bay and how it works on the coat and a thread on BadAs*Brown that shows several members horses of that range of color as it expresses very differently. I'll see if I can dig them up or at least pictures to show it..


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## QtrBel (May 31, 2012)

Now if it would just let me post. Don't know what is up with this site some days. Here is the thread on browns... http://www.horseforum.com/horse-colors-genetics/badass-brown-92038/


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## Crazy4horses2 (Jul 12, 2017)

This is one I could find of her (Dakota) that showes the tanish brownish color I'll go through my pics on my laptop later and see if I can find better ones


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## QtrBel (May 31, 2012)

It would help to see both sides That looks like she could well be brown with the muzzle marked like it is. Do you have winter pics? I assume this is summer? Don't know why I thought she was a he. If you go to the BAB thread linked there are some really dark bays (seal brown) that look black. You can see what I mean about the cinnamon coloring on the muzzle and soft points. I'll see if I can find one of a friend's and post it.


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## QtrBel (May 31, 2012)

Here is one. Couldn't find a winter pic but the cinnamon color still shows up on her late spring.


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## Crazy4horses2 (Jul 12, 2017)

I don't have any winter pictures of her as I just got her a few months ago that picture was taken in the beginning of may the previous owners really didn't give a hoot about her that's why they just gave her to me. I will try to find good pictures of her from both sides but they are all on my laptop that one and my avatar pic are the only ones I have on my phone lol


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## Crazy4horses2 (Jul 12, 2017)

I have no idea why that double posted...


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