While on the topic of pinto patterns....

[Becky]

Hmmmm....... this is interesting. I didn't know pattern genes would be linked to color genes. That's even more to think about and try to comprehend!

 

[Charlotte]

I have wondered in one case if pattern (tobiano) could be SEX linked! At least in one mare of ours. She is a chestnut tobiano/splash/maybe sabino too.

Out of her first 6 foals

3 were black pinto fillys

3 were chestnut pinto colts

2011 blew the record as we got a solid black colt.

So?????

 

[targetsmom]

This has been a real eye-opening experience!!! Thanks for sharing everyone. But I did find one thing on the APHA website that reminded me not to trust everything you read on the web:

"No homozygous splashed white horses have ever been documented, leading to the suspicion that this is yet another gene that cannot exist in homozygous form."

I know Joanne just posted at least one, and I think two, of her horses that tested homozygous for the Splashed White-1 gene.

 

[Becky]

APHA has been known to have inaccurate information regarding patterns on their website. I sure wouldn't look to them for pattern info!

Charlotte, your one colt blew your theory completely! LOL

 

[ohmt]

I only posted the APHA article because I am on my phone and I couldn't find the one that I read earlier, which is from a very reliable website (I will post it when I get to my computer later). The APHA article covered the basics of the tobiano and extension link which is what I was trying to share. I believe what they are referring to are the SW-2 and 3 which are found in "big" horses are are thought to be lethal in homozygous form.

Charlotte-what is/are the colors of the sire(s) of the foals of your mare and do you know the homozygous/heterozygous status of their colors/patterns that you could post?

 

[Becky]

ohmt, what you posted makes good sense and is likely true. I was referring mainly to the statement that homozygous splashed white horses don't exist, when we know, for a fact, that they do.

 

[Lewella]

Yes Amanda you are on the right track.

Here's the simplest way to explain linkage that I know. I love this example because he makes it SOOOOO easy to understand! True roan and tobiano are both linked to Extension (Extension is the location of the black and red genes and that is why they are coded E for black and e for red).

There is a Shetland stallion named King's Dicky Doo VB. He is a blue roan tobiano. His tobiano is red linked (eTo) and he inherited it from his dam. His roan is black linked (ERn) and he inherited it from his sire. Because of his linkage he passes eTo and ERn and when you start showing his produciton it makes it pretty obvious. When bred to solid colored mares if he produced solid colored foals they were roans and black based, when bred to solid colored mares if he produced tobiano he did not produce roan.

During genetic recombination (which is when genetic material is swapped from one chromosome of a pair to the other chromosome of the pair during the formation of eggs and sperm) linkage can break. The closer genes are located to each other the less likely they are for a linkage break to occur. Extension and Tobiano are very close together (as are Extension and Roan) so the linkage does not break often. There haven't been any major studies on how often they do "unlink" but 7% is probably as close to accurate as we are going to get without a major long term study.

The color calculators online aren't programmed to take linkage into consideration.

As for sex linkage - there are no color genes known to be located on the X or Y chromosome at this time. Extension, Tobiano, and Roan are on Chromosome 3.

 

[ohmt]

Thanks Lewella! I really do learn something new every day. Here I thought I had the basics down, and BAM. Something new thrown in the mix. I'm excited to take a look at the rest of my tobianos and see what I can find.

 

[valshingle]

I'm trying to wrap myself around this pinto linked to Extension subject.

What can you tell me based on this mare? She is a lab tested silver chestnut tobiano with grey: ee nZ TT Gg aa:

Bred to black app - produced tT nZ ee Gg pintaloosa (phenotype, didn't actually test, silver deduced due to rapid rate of greying out)

Bred to silver black pinto - produced tT nZ ee gg (didn't test for agouti)

Bred to buckskin pinto - produced TT Ee Aa nZ gg negative for cream

Can you say which extension her tobiano is on?

 

[ohmt]

It would be linked to a red. I believe it is only red/black and roan that are linked with tobiano, so other modifiers, like silver and grey are not linked.

Now your buckskin I can say probably has his linked with black if there wasn't crossover.

 

[valshingle]

Thanks for your reply. The silver bay pinto foal also has one blue eye and both parents have 2 brown eyes each - the mare is LWO negative, the stallion is untested, but doesn't look overo to me (see below). I am assuming the blue eye is from splash as the foal is negative for LWO also.

Now to confirm this:

The buckskin pinto stud, who has not been color dna tested, also produced this:

Ee Aa nCr solid

who's mother is EE Aa solid.

OHHHHH! I get it. The stud must be Ee, so he gave the e to this foal and that's why it's solid. I had thought that the stud was homozygous based on his pinto pattern, but apparently not (both of his parents are pintos):

Buckskin sire, see the roaning on the shoulder?