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Announcement re Roan/Tobiano's!

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tbtash
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Announcement re Roan/Tobiano's!
Thought I would post this interesting announcement on the Animal Genetics site, sorry if this has already been discussed. So if we understand this right, if you have a tobiano + roan horse it is in a sense homozygous for a white pattern and will never breed a solid foal? Like a Pearl and Cream carrier can not throw both but will always throw one or the other. Also opens up a debate re roans.. should they be seen and classed the same as Paints?? RECENT UPGRADES 6/10/10: We have changed the calculator to take into account that Roan and Tobiano are mutations of the KIT gene found on horse chromosome 3 and thus will not occur on the same branch of a horses chromosome pair. This means that a horse that carries both Tobiano and Roan can only be heterozygous for each gene and will pass one or the other to its offspring and not both or none. This is also the case for Sabino1 and the known Dominant White mutations which are also mutations of the KIT gene. We have not yet made the change for Tobiano/Sabino or Roan/Sabino combinations but plan to in the near future.
Jenks
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Re: Announcement re Roan/Tobiano's!

Eh...I took it to mean that a horse that is both Tobi and Rn? - it can only pass one of the two genes, not both.

Danni
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Re: Announcement re Roan/Tobiano's!

That's interesting, I didn't realise that. I also don't completely understand it :oops:

So it's saying that for example, you couldn't have a horse be homozygous tobiano, and have roan at the same time. Why? Even if both are on KIT, they aren't in the same place, so why can't have both? I must admit I never completely understood the whys of pearl/cream thing either. :oops:

Morgan
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Re: Announcement re Roan/Tobiano's!

:roll: They didn't account for crossover.

yes they are close together and almost always passed on as a unit. so if you cross a tobiano to a roan and get a tobiano roan the most likely chromosome for that horse will look like this:
Chromosome DNA strand 1:-----To------rn--------- (from tobiano parent)
Chromosome DNA strand 2:-----to-------Rn-------- (from roan parent)
and they will pass on only one of these strands to offspring so you get have roan and half tobiano babies.

but sometimes the strands will cross over and recombine while being copied. Imagine those two lines above are being put together and they get tangled up and stuck together somewhere between the tobiano and roan locus. They can then be cut apart and put back together with the ends from each other and the foal would have this instead:
strand 1:------To------Rn-------
strand 2:------to------rn--------

now THIS horse will pass on either roan and tobi together or only solid. I saw a stallion once that throws blue roan tobianos and red solids. The black, tobi and roan were all coming as a package of all or none :lol:

Now is it possible to breed the above horse to a roan or tobiano and potentially get a horse that is both and homozygous for one. Breed two of those together and you have a 25% chance of a horse that is homozygous for both roan and tobiano.

Extension is also on the same chromosome so similar factors apply to breeding for "double homozygous" black tobianos. And everyone knows they exist.

Basically if you breed roan to tobiano enough times, eventually there will be an exception and then that bloodline will be linked the other way. The whole pearl/cream thing is possibly because there simply hasn't been enough bred together yet or else they are very very close together making crossover more improbable. The chances would increase the more creams and pearls were bred together. But once it does happen in one horse that horse will pass both on together.

Danni
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Re: Announcement re Roan/Tobiano's!

I know a tobiano/roan stallion, and he throws roans, tobiano roans, normal tobi's and solids (well I'm pretty sure he's thrown solids, does this info mean he shouldn't have??) He's bred to a lot of tobianos, so I assume then that the tobiano came from the mare on the tobi/roan foals and none of the foals could be homozygous tobiano as well as roan? Well except for this crossover thing....

Gosh I'm getting confused I think, I just had the red/black thing with KIT sorted out in my head and now I'm all confused again!! LOL!!

Morgan
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Re: Announcement re Roan/Tobiano's!

It's not really that hard. Just make a normal pundit square and put the linked genes in the same boxes together (like To/rn in one box and to/Rn) in the other.
Now identifying how the genes are linked in the individual can be tricky, especially if they are bred to others than can contribute the same genes.
1st look at the parents, the majority of horses will not have had a crossover and so you can figure it out easily from the parents.
It sounds like the stallion's roan and tobiano are not together but that would make solids unlikely. IF his is tobiano linked to non-roan and roan linked to non tobiano than there are some posibilities for the solid foals: they are not true solid, either minimal roan or tobi. Or they were a crossover. (or product of a fence crosser XD )
Also might make sure that he is actually roan and not sabino or rabicano :)

accphotography
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Re: Announcement re Roan/Tobiano's!

I don't know that I'd be concerned about the crossover between genes ON KIT, I'd only be concerned about the crossover between KIT and extension. I'll have to go see how they've done this as without inputting the info as to which gene it's tied to it won't be accurate.

I just wanted to clarify one thing. It WOULD be possible to have a homozygous tobiano with roan or homozygous for both, etc. It might take a crossover, but it's perfectly possible.

The tobiano/roan linkage situation is NOT like the cream/pearl situation. Roan and tobiano are separate mutations that just happen to be closely linked. Cream and pearl are separate alleles of the SAME gene. No matter what you do you can never have a homozygous cream with pearl, and that IS possible with tobiano/roan.

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Danni
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Re: Announcement re Roan/Tobiano's!

It's not really that hard. Just make a normal pundit square and put the linked genes in the same boxes together (like To/rn in one box and to/Rn) in the other.
Now identifying how the genes are linked in the individual can be tricky, especially if they are bred to others than can contribute the same genes.
1st look at the parents, the majority of horses will not have had a crossover and so you can figure it out easily from the parents.
It sounds like the stallion's roan and tobiano are not together but that would make solids unlikely. IF his is tobiano linked to non-roan and roan linked to non tobiano than there are some posibilities for the solid foals: they are not true solid, either minimal roan or tobi. Or they were a crossover. (or product of a fence crosser XD )
Also might make sure that he is actually roan and not sabino or rabicano :)

.....

Ok, if we go back to cream/pearl. We are told a cream/pearl stallion has to throw either cream or pearl. Can't pass both. You are saying this is because he got cream from one parent and pearl from the other, so they are on a separate chromosomes, thus only one can be passed on? So there was crossover, both could end up on the same chromosone and then both or neither would be passed on??

And now we are saying roan and tobiano works in the same way?? But isn't pearl sort of a mutant cream, roan isn't really related to tobi the same way is it??

accphotography
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Re: Announcement re Roan/Tobiano's!

Bingo to your last sentence. Pearl is a cream mutation/allele. Roan and tobi aren't related except to be near each other on KIT. But pearl and cream are virtually one and the same in a way (kinda... just trying to express the difference between roan/tobi and pearl/cream).

We've SEEN homozygous tobianos with roan. We know they can have both since they are separate mutations.

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Danni
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Re: Announcement re Roan/Tobiano's!

Bingo to your last sentence. Pearl is a cream mutation/allele. Roan and tobi aren't related except to be near each other on KIT. But pearl and cream are virtually one and the same in a way (kinda... just trying to express the difference between roan/tobi and pearl/cream).

We've SEEN homozygous tobianos with roan. We know they can have both since they are separate mutations.

Ok to get a homozygous tobi with roan, the horse passing on both tobi and roan would have them linked and always pass on both or neither? And if passed on both to a foal who got another tobi from dam, you could get the homo tobi with roan? But usually a horse would get roan and tobi from different parents so would only pass on either one?

I think I'm getting it..?

P.S. and Morgan, yes I think the stallion I'm thinking of couldn't have tobi and roan linked, so solid is either not his or not solid!

accphotography
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Re: Announcement re Roan/Tobiano's!

BINGO!!! You got it!

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tbtash
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Re: Announcement re Roan/Tobiano's!

Ok... so who can show us a horse--that has been proven to be a homozygous tobiano with the classic roan gene?? :smile:
also how rare would the crossover thing be?? in percentage, does anyone know?

accphotography
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Re: Announcement re Roan/Tobiano's!

I will find one... I had one bookmarked at one point.

Pretty rare from what I understand. I'd guess 3% or less. Horsegen would know better.

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Songcatcher
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Re: Announcement re Roan/Tobiano's!

Wow! Extremely interesting, but I've got to admit it really baffles me. This crossover talk makes me feel like a kindergartener in high school. Keep talking. I'll keep listening, and maybe I'll get it. Eventually.

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Jenks
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Re: Announcement re Roan/Tobiano's!

Morgan - I LOVE your new card!!! Do you do consulting? I need a consult.

horsegen
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Re: Announcement re Roan/Tobiano's!

The percentage of crossovers expected between any two points on a chromosome is completely dependent on how far away those two points are. Those two points can be in two different genes, or in the same gene. The closer they are, the less chance of crossover.

Roan and Tobiano are two mutations in the same gene--KIT (we think...technically, roan hasn't been identified, but mapping data puts it squarely in KIT). Cream and pearl are two separate mutations in the same gene--MATP. There's no real difference between the two scenarios, except that roan and tobiano are (most likely) a little farther apart than cream and pearl, so we would expect crossover between them more often than the MATP mutations. However, in both scenarios, they are very close, and crossovers will be extremely rare. Probably less than 1%.

I'm not really sure what Animal Genetics is saying in this instance, but my interpretation is that because they have yet to identify a horse that has tobiano and roan on the same chromosome, and because a crossover causing this phenomenon would be so rare, they're just removing it from their possibilities.

Morgan
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Re: Announcement re Roan/Tobiano's!

The thing is, once it DOES happen, that entire bloodline will be linked that way so you can't throw it out of horse posibilities :S
See look I found one:
http://www.bffarms.com/mares.cfm" onclick="window.open(this.href);return false;
scroll to Two M Finally and her daughter Two M Colonel Finally. Both are throwing roan tobianos and solids.

Morgan - I LOVE your new card!!! Do you do consulting? I need a consult.

sure :-D send me a message

Daylene Alford
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Re: Announcement re Roan/Tobiano's!

Cream and pearl are two separate mutations in the same gene--MATP.

So theoretically you could have a horse that was homozygous for cream with pearl added?

Monsterpony
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Re: Announcement re Roan/Tobiano's!

Theoretically yes, but very unlikely. I believe that would be the equivalent of being homozygous EE with an e added.

.

horsegen
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Re: Announcement re Roan/Tobiano's!

So theoretically you could have a horse that was homozygous for cream with pearl added?

Theoretically, yes. A horse could have cream and pearl on one chromosome, and just cream on the other. Theoretically, a horse could also be homozygous cream and homozygous pearl. The incidence of either of these occurrences is extremely unlikely due to the small chance of the crossovers necessary in the population to make it happen, but is possible.

I believe that would be the equivalent of being homozygous EE with an e added.

Well, actually that's NOT possible. "E" is the wild-type allele for extension. It represents a fully functional copy of extension with NO mutations. So by definition, "E" means "not e". If a horse is EE, that means that both copies of extension are mutation free, thus are not e.

RiddleMeThis
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Re: Announcement re Roan/Tobiano's!

Is "A" the wild type as well?

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tbtash
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Re: Announcement re Roan/Tobiano's!

Morgan- Checked out those mares, interesting..
Mum bay roan tobi (Two M Finally) threw a solid bay this time-- her daughter also a bay roan tobi (Two M Colonel Finally) threw a bay roan no tobi??

So Mum is the crossover-- but daughter is not??

:?

any homozygous tobi + roan out there??? ;-)

Morgan
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Re: Announcement re Roan/Tobiano's!

ahh now I'm confused LOL I was sleepy and didn't see the "solid bay roan" part. I think my brain saw "solid" and took it to mean no paint, no roan.
lets see:

Momma: Bay Roan Tobiano, and that is for sure classic roan.
Colt: Bay solid. Bay AQHA sire.
Daughter: Bay Roan Tobiano. Black AQHA sire

Daughter throws Bay roan....and I checked the foals page, color appears very much correct without so much as a sock and sire is plan ole bay Frame.

*head explodes*

horsegen
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Re: Announcement re Roan/Tobiano's!

Is "A" the wild type as well?

Yes, "A" is considered the wild type.

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Re: Announcement re Roan/Tobiano's!

Daughter throws Bay roan....and I checked the foals page, color appears very much correct without so much as a sock and sire is plan ole bay Frame.

Could be one of those extremely minimal roan expressions like that stud that appeared solid, but threw a lot of roan babies.

.

Morgan
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Re: Announcement re Roan/Tobiano's!

I'm not so sure, I can't find any evidence of him being roan and she's done it before with a different stallion. Everything right now seems to point to Two M Finally being roan linked tobiano, and first generation at that, and her daughter being NOT linked. Which is just....wow....

Two M Panquitch (Tobiano) x Two M Silver (Roan) = Two M Finally (Roan Tobiano)

Two M Finally (Roan Tobiano) http://content.breederoo.com/users/sueho..." onclick="window.open(this.href);return false;
x Colonel Back in Black (Black) = Two M Colonel Finally (Roan Tobiano)
x Secretly Regal(bay) = Jest A Regal Gal (Roan Tobiano) http://content.breederoo.com/users/sueho..." onclick="window.open(this.href);return false;
x Secretly Regal(bay) = Regal Mapel Sugar (bay) http://www.bffarms.com/foals.cfm" onclick="window.open(this.href);return false;

Two M Colonel Finally (Roan Tobiano) http://content.breederoo.com/users/sueho..." onclick="window.open(this.href);return false;
x Badger Zad (black overo) = Badger Zappedin Forst (Roan) http://content.breederoo.com/users/sueho..." onclick="window.open(this.href);return false;
x Barefoot Ruckus Raider (bay overo)= Raider Maid Spottless (Roan) http://www.bffarms.com/foals.cfm" onclick="window.open(this.href);return false;

Horsegen? help? :-\

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Re: Announcement re Roan/Tobiano's!

OK, small words in your answers, please ymwhisle
The stallion is supposed to be H/Z Tobi and H/Z Roan??
The foal, which is not solid but minimal Tobiano + Splash.....the "solid" bit refers to him not being Roan??
Is it unlikely to get a Tobi H/Z Roan, then??
Or is it thought to be unlikely to get a Tobi Roan (cos it obviously is not)
I seem to have failed to pick up the whole point, and would be glad of a bit of help here!

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Danni
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Re: Announcement re Roan/Tobiano's!

My understanding is that most horses that are tobiano and roan, got tobiano from one parent and roan from the other, therefore unless some sort of crossover occurs then they can only pass either the tobiano or the roan to their foals. Not both. It therefor makes it very very uncommon, but not impossible, for a horse to be tobi/roan and be homozygous for either the roan or the tobi, or both! Obviously uncommon enough that it's not even going into the foal colour calculator.

I think that's how it works...?

accphotography
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Re: Announcement re Roan/Tobiano's!

Well I did find a tested SB1SB1 TOto.

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lillith
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Re: Announcement re Roan/Tobiano's!

Ok, I am now a bit lost.

As I undertand, Tobi is a massive inversion before KIT, seems that they code the same but in a different order Roan is KIT based but not isolated. I cannot see why you cannot have both on the same chromosome otherwise having Sabino and Tobi on the same chromosome would be impossible as it is also a KIT mutation?

Tobi inversion I think:
AHD1C KDR CLOCK ALB CCNI ENOPH1 WDFY3 PDLIMS KIT PDGFRA TEC GABRB1
AHD1C PDLIM5 WDFY3 ENOPH1 CCNI ALB CLOCK KDR KIT PDGFRA TEC GABRB1

How exactly doe the linkage work?

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rabbitsfizz
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Re: Announcement re Roan/Tobiano's!

Thanks, I understand that :toast

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