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Announcement re Roan/Tobiano's!

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accphotography
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Re: Announcement re Roan/Tobiano's!

If they said the horse could inherit sabino1 independently of tobiano are they not essentially saying it IS possible???

IMAGE(http://i173.photobucket.com/albums/w65/accphotography/Misc/Sig.png) IMAGE(http://phrf.pitapata.com/uno2m5.png)

Ammit
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Re: Announcement re Roan/Tobiano's!

They are more then just linkages they are effectively different alleles of the same gene. Keep in mind genes like creme and pearl may not be any further apart then roan and tobi for example. Crossing over would be hypothetically possible but statistically so slight a chance as to be effectively impossible. That is the change the color calculator people where referring to in the OP.

Ammit
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Re: Announcement re Roan/Tobiano's!

If they said the horse could inherit sabino1 independently of tobiano are they not essentially saying it IS possible???

Never on a homozygous horse. 1 stand of DNA one variation of KIT never more then one. If you read it in context it is clear that Davis is saying one gene from each parent. Never two genes from one parent.

lipigirl
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Re: Announcement re Roan/Tobiano's!

This thread is very interesting. Not too sure I have it all wrapped up yet like most of us but am unravelling it slowly.

Anyway one of you guys can state in stage by stage in Layman's terms for some of us who are more practically minded then theoretical......i struggle when it gets too theorectical.

Ammit
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Re: Announcement re Roan/Tobiano's!

To super over simplify, DW, Sabino (1 at least), Tobiano, and Classic Roan are all one gene, just like Black and chestnut are one gene just different versions.

Jenks
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Re: Announcement re Roan/Tobiano's!

So there's a spot for one on each side of the double helix. Can't fit two on one side......(?)

Ammit
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Re: Announcement re Roan/Tobiano's!

You got it just one per side.

Jenks
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Re: Announcement re Roan/Tobiano's!

:D Makes perfect sense!

lipigirl
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Re: Announcement re Roan/Tobiano's!

Thanks...NOW I get it and hence why you can't have both Tobi and......... :ymsmug:

lillith
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Re: Announcement re Roan/Tobiano's!

Ok I think I may be getting it, please be patient.

:BH - feeling dense

Can you have a homozygous tobiano that is also homozygous roan? or Sb1?

I might be repeating myself but it takes repetition for me to get it....... I drew some pictures to try to help.

Tobiano is a HUGE inversion of a set of loci before KIT,
IMAGE(http://i8.photobucket.com/albums/a36/scarlet-wolf/Tobi.jpg)

Sb1 is an intron mutation that splices out exon 17 of KIT and roan is linked to a substitution of exon 19 of KIT
IMAGE(http://i8.photobucket.com/albums/a36/scarlet-wolf/KIT.jpg)

How does the linkage work, I can't see why you cannot have the inversion before KIT, the splice at 17 and the substitution at 19. Or am I being dense and you can have all, some or none on a chromosome but if they are there then they will be passed on together or not at all.

Ok, VERY over simplified picture, correct?
IMAGE(http://i8.photobucket.com/albums/a36/scarlet-wolf/crossover.jpg)

If this is the case how does the linkage to Extension work? is it close to KIT? I know it is on ECA3.

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a fairly pointless little piece of cyberspace where I post random thoughts on just about anything, if you're bored any comments are welcome.

Ammit
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Re: Announcement re Roan/Tobiano's!

The problem is your images are so far off scale that I think they are confusing you. You need to remember the numbers we are dealing which. People think crossing over is just a given in meiosis but it is not. It really decently rare.. If it common we would have a lot more genes getting broken all the time. As I said before, extension and KIT are on the same chromosome but they are some hundred million base pares a part. And we really do not see crossing over between these too very often. It is a once in a (human) lifetime of breeding horses sort of event. Your example for the green Sb-1 compared to the red tobi is more like how far extension and KIT are apart. Your band you gave for tobi is several times larger then all of Kit and it's controllers. We are talking a few hundred thousand base pairs only. Yes tobi might be in a controller function but we are still talking the same loci. (Remember: a gene is a segment of DNA that codes for a specific protein, but the loci is the location of that gene and it's controller functions) Just because tobiano is just outside of the gene proper does not mean it is not part of KIT. That is why I feel the proper way to denote tobiano is as KIT superscript to. Because really we are talking about one gene here.

As a further strike against the idea I plan to do some research into how crossing over works, I do not have much more then a basic textbook knowledge of it. It is possible that crossing over can only happen in certain denoted regions which would mean it would be completely impossible for crossing over in the middle of a gene like that to occur. But as I said I have not done the research yet so I do not really know. Part of the reason I am building my blog (http://www.abitofscottandellie.com/" onclick="window.open(this.href);return false;) it to simply start creating a repository for all the stuff I want to research just to keep it all straight.

Another important thing to note, a foal with a KIT gene that is too heavily disrupted dies. So it is possible that putting additional disruptions of the KIT gene on top of the already wacky results of tobi (talking about on a single strand here) could result in a lethal foal. We do not really know enough about how the whole thing works from start to finish to make accurate predictions but there are some journal articles out now that show promise in unraveling this mess.

As a final thought I am very excited to see you note where the mutation for roan is! Have they published yet? And do you know if this substitution is complex or simply a single base pair? It is neat to see how a small amount of change to KIT causes a small amount of white markings while a larger change disrupts quite a bit of the pigment. Since homozygous sabinos, and dominant whites all exhibit much more extensive markings (DW's to the point of death) then when heterozygous it would be interesting to do a bit of a study to see if homozygous roans can be more heavily marked then heterozygous ones. I know there is no drastic correlation like with sabino-1 but it would still be neat to see if it does have some effect.

Ammit
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Re: Announcement re Roan/Tobiano's!

I also want to add an additional comment that since sabino-1 is just before 17 and roan is at 19 we are talking a few hundred to a few thousand or so base pairs between them. Tobiano bumps right up next to kit. The span between tobi and roan or sabino is a few tens of thousands of base pairs. With the whole lot being a few hundred base pairs long. If crossing over was going to happen it would be much more likely for it to hit right in the middle of the tobiano inversion (in fact several levels of magnitude more likely) and totally muck up tobiano then it would be for sabino-1 or roan to become linked with it. And depending upon the exactly what happened to cause them it may even be more likley to spontaneously generate roan or sabino-1 then to have tobiano linked with either one on the same strand of DNA. We certainly see dominate white mutations pop up spontaneously pretty frequently. If sabino was more easy to spot and identify we might be able to say the same thing about sabino.

lillith
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Re: Announcement re Roan/Tobiano's!

Sorry, now I have to remember where I read that about roan, I think it was related to the zygosity test they offer in QH, Roan was linked to but not mapped to an exon 19 substitution. I will see if I can find it when I get back from work.

I am trying to get my head around the sizes/distances we are talking about but it is slow going, I have to break everything down into the simplest concepts and build it up to get it.

Thanks for the reply, I am still a little lost though, on the very basic and not to scale drawing I did was I right about the results?

And did I get the concept right with my excel pics?

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a fairly pointless little piece of cyberspace where I post random thoughts on just about anything, if you're bored any comments are welcome.

Ammit
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Re: Announcement re Roan/Tobiano's!

Honestly I have no idea what you where trying to show specifically in any of the images so I can not say if you where right, the one of the chromosomes however is quite incorrect. There is no such thing as tobi and roan on the same strand.

accphotography
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Re: Announcement re Roan/Tobiano's!

There is no such thing as tobi and roan on the same strand.

I think THAT is exactly what she was trying to figure out for herself (because her example shows that very thing being/happening).

As I said before, extension and KIT are on the same chromosome but they are some hundred million base pares a part. And we really do not see crossing over between these too very often. It is a once in a (human) lifetime of breeding horses sort of event.

Really? 7% is only once in a lifetime? One of our own forum members has had it happen at LEAST twice out of 7 breedings. It happens a fair bit in the tobi Warmbloods too. I've just never considered it rare. Unusual, but not rare by any means.

IMAGE(http://i173.photobucket.com/albums/w65/accphotography/Misc/Sig.png) IMAGE(http://phrf.pitapata.com/uno2m5.png)

lillith
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Re: Announcement re Roan/Tobiano's!

Right got it, so a homoxygous tobi cannot have roan and a homozygous roan cannot have tobi?

Got it.

hmmm.....can they have Sb1?

If not it would point to something that we tend to call 'sabino' not being KIT related and splash being further away because you can definately get sabino/splash and homozygous tobiano thogether.

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a fairly pointless little piece of cyberspace where I post random thoughts on just about anything, if you're bored any comments are welcome.

accphotography
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Re: Announcement re Roan/Tobiano's!

hmmm.....can they have Sb1?

If not it would point to something that we tend to call 'sabino' not being KIT related and splash being further away because you can definately get sabino/splash and homozygous tobiano thogether.

According to Ammit, nope.

Indeed it would. I've been pondering that too.

Some people (read, even researchers) believe that tobiano CAN and DOES cause face white. This could be further evidence of that.

IMAGE(http://i173.photobucket.com/albums/w65/accphotography/Misc/Sig.png) IMAGE(http://phrf.pitapata.com/uno2m5.png)

Ammit
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Re: Announcement re Roan/Tobiano's!

According to UC Davis nope. :roll:

Honestly I am not inclined to take none substantiated facts from you as truths. Nothing personal but I have seen no reason to believe your reports on data are to be trusted. You can continue to try and pick holes at things over and over all you want, but personally I will stick with the accepted science. Feel free to believe what ever you want but just trying to pick holes in things, for the sake of it, is starting get petty. You where confused about crossing over between tobi and roan. It is ok. Move on.

Ammit
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Re: Announcement re Roan/Tobiano's!

lillith sabino the term is just a phenotype. It is possible that some lines of tobi do have a KIT mutations that is sabino like (or true sabinos but not sabino-1 as seen so far), it is also possible that tobiano itself causes sabino like markings. At this time splash is not thought to be related to Kit (remember KIT likes dark eyes even in extreme form, and tends to like dark heads, but splash likes blue eyes and white heads). Splash has a solid chance of not even being on the same chromosome as KIT and extension. So some sabino like marks are KIT some may not be KIT at all, and a good deal of what gets called sabino is splash as well. Until we have a solid consensus of what the phenotype sabino actually means we have to assume that sabino like markings can be caused by lots of things.

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

Honestly I am not inclined to take none substantiated facts from you as truths. Nothing personal but I have seen no reason to believe your reports on data are to be trusted. You can continue to try and pick holes at things over and over all you want, but personally I will stick with the accepted science.

I'm sorry, you can think it all you want but there was no reason to bring this back up. I was hoping we had things settled.

The 7% figure actually comes from Horsegen (former UC Davis geneticists). She is in the process of moving to a fellowship in Boston or I'm sure she would have jump in before now on this thread.

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

Here is the thread where we discussed the chance of cross over between extension and kit/tobiano.

http://forum.equine-color.info/viewtopic..." onclick="window.open(this.href);return false;

lillith
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Re: Announcement re Roan/Tobiano's!

I wasn't aware that whatever causes the splash phenotype was thought to be further away, makes sense though.

I know that sabino is a phenotype I was simply saying that not being able to have Sb1 and Tobi together would suggest that some of what we call sabino is caused by something further away from KIT.

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a fairly pointless little piece of cyberspace where I post random thoughts on just about anything, if you're bored any comments are welcome.

lipigirl
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Re: Announcement re Roan/Tobiano's!

I wasn't aware that whatever causes the splash phenotype was thought to be further away, makes sense though.

I know that sabino is a phenotype I was simply saying that not being able to have Sb1 and Tobi together would suggest that some of what we call sabino is caused by something further away from KIT.

Yes that is because we tend to blame sabino for just about any white that we can't pin down....but not neccessarily sabino 1...get it ?

Ammit
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Re: Announcement re Roan/Tobiano's!

Obviously this is not a place where I am going to fit in. Just not the atmosphere of real study of science I was hoping to find, but not every site is for everyone, and a site that promotes what I have seen is not for me. I harbor no hard feelings to the site admin and wish her the best. So many cooks can not survive in one kitchen. I wish you the best of luck.

Best make you color calculator a good one, mine is already mostly functional, and I look forward to seeing them compete. :-D :lol:

And I was not going to mention this to save face for acc but what the heck. The owner of that website said she had never spoken to you in her life. ;-) ymwhisle

Chow!

horsegen
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Re: Announcement re Roan/Tobiano's!

I'm really late contributing here, sorry! It has less to do with my move to Harvard and more to do with the fact that I had a baby last week! I'm just now poking my head out and looking around at the world again.

This is a really interesting thread...I've enjoyed reading it. I have very little else to contribute that hasn't already been said, but both sides of this discussion are right. Tobiano, roan, sb-1, DW are all found either in KIT or near KIT. (The mutation causing roan has not been identified yet, but it's linked very strongly to KIT, so it has something to do with that gene.) I have never seen a horse that had more than one mutation of KIT on the same chromosome...the main reason for this is that these mutations arose independently of each other and have been passed down from ancestral sources, so the only way you could get two of them on one chromosome would be a) for a horse with one of these mutations to spontaneously develop the other on the same chromosome (a chance so slight as to be not worth discussing) or b) for crossing-over to happen in a horse that carried one mutation on each strand. Ammit is right...we're talking about a very small distance between these mutations and the chances of crossing over occurring are very, very small. (I said that somewhere...was it this thread? A different thread? God, I need sleep.) That's not to say it couldn't ever happen...but as far as we can see, it sure hasn't happened yet.

The linkage between extension and KIT isn't so tight. I've seen a few extension/KIT recombinants in my lifetime, so it does happen. The percentage is tough to figure out, because it is pretty rare, and honestly we don't really use recombination frequency when talking about the horse map anymore now that the whole genome is sequenced. I've seen estimates ranging from 3% to 7%...based on the distance between genes, I generally go with 7%, but these are really guesstimates. It's all about what happens in real life when you talk about crossover frequency, and these genes recombine rarely enough that it's hard to judge what that frequency actually is.

Okay, baby's waking up and he's hungry...

lipigirl
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Re: Announcement re Roan/Tobiano's!

Congratulations Horsegen !!!! How are you feeling, can you post a new thread when you have time and share some pictures.

lipigirl
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Re: Announcement re Roan/Tobiano's!

As to Ammit, you have had some very valid points and we don't want to lose you, shame that you feel that way, we have had a lot more heated discussions on here before without people leaving......oh well !

RiddleMeThis
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Re: Announcement re Roan/Tobiano's!

Obviously this is not a place where I am going to fit in. Just not the atmosphere of real study of science I was hoping to find, but not every site is for everyone

You mean the atmosphere of "everyone listens to me and believes everything I say without question or discussion" wasnt here.

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

You mean the atmosphere of "everyone listens to me and believes everything I say without question or discussion" wasnt here.

This is unnecessary. Please everyone keep all catty comments to yourself. They have no place here.

Songcatcher
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Re: Announcement re Roan/Tobiano's!

I have been reading this thread from the beginning. I have gone from feeling like a kindergartener in high school to feeling like a first grader in college. I don't understand 90% of what I'm reading (maybe 99%) but I do know that the more I read, the more I understand. I really hate that some people feel the need to snip at each other to try to reinforce their position. Right or wrong, a continued, civil discussion helps in understanding. I hate for anyone with good ideas to leave :-t and also hate for arguements to get ugly. :argue

In spite of all, I feel I have a better understanding of this genetics stuff than I did before. I hope the discussion will continue and hopefully I will continue to understand more. :ympray:

Freeland Nash Valliant, OK 74764 www.songcatcherranch.webs.com

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