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Some genes I am confused about - homozygousity & OLWS

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Shawneen
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Some genes I am confused about - homozygousity & OLWS
Ok a quickie about me - I am absolutely GAGA about black and white Overos!!! They are my absolute favorite. A problem I have run into lately is finding the right conformation within the potential stallions I find - which is really a whole other story(they are nearly non-existant and I am rather picky). Recently I bought Chance(grulla) and Cody(dun) who are full sister and mother to one of the mares(red dun) I had already bought. I have a serious grulla fetish growing now! So I'm sitting here doing my wonderful color research about my mares, and it dawns on me, a big freaking DUUUUUUUH! I have a grulla now - when bred to homozygous black I will get either black or grulla, no ifs, ands, or buts. So I'm all juiced even if I have to wait a few years because she's only 3 and I want to get her fully trained with miles on her before I breed her. My question I guess, while thinking about all this... She is not homozygous obviously because she has a red dun full sister. So at what point can a horse become homozygous? There is tons of color research, but I haven't seen a whole lot on when and how homozygousity occurs. A potential stallion I have found for whichever mare I choose to breed is homozygous, but his grandsire on his dams side is the sire of my gelding(the alien bay with silver points) and he was NOT homozygous. Another questions is about OLWS. My mom has a dun Paint mare whose grandsire 3 gens back on her sire's side was Gambling Man. He was OLWS+. He is also this stallions sire, and he is also OLWS+. Of course if my mom agreed to let me breed this mare I would get her tested first, I have already tested my black and white mare and she is OLWS+ so that's a no go. Correct me if I am wrong please. All frame overos are not OLWS+. I am wondering how exactly it is passed on. I can't find this information. I have read a lot about it but have never come across whether it is ALWAYS passed on if there is a + parent. I hope you understand what I am asking LOL I would in no way, shape or form breed two OLWS+ horses to each other. I am just trying to get a better understanding on the genetics of it. Thanks and sorry for the long post :)
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Re: Some genes I am confused about - homozygousity & OLWS

Ok it sounds like you need some basic genetic inheritance information.

Each horse carries two alleles of each gene. When a horse is bred it passes one allele of each gene, thus one allele comes from the dam for gene 'purple' (for example) and one allele from the sire for gene 'purple'. Every gene known in horses at this point (with possible exception of agouti) has only two alleles, a dominant (shows the phenotype) and a recessive (no change in phenotype).

All LWO+ horses are 'Oo' (one dominant, one recessive as two dominants is lethal). When an 'Oo' horse is bred it passes 'O' 50% of the time and 'o' 50% of the time.

This scenario is the same with homozygous black. If both parents are 'Ee' then the foal has a 25% chance of inheriting the 'E' from both parents and thus being homozygous. There is also a 50% chance of 'Ee' (heterozygous black) and a 25% chance of 'ee' (red). Because black is dominant, all 'Ee's will be black based. In that case you only ever need an 'EE' sire or 'EE' dam to produce a black foal, not both.

Hope that helps. Ask more if you need to. The basic genetics article on this site might help you as well.

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Shawneen
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Re: Some genes I am confused about - homozygousity & OLWS

Ok I think I was confusing myself. I know how the genes are passed and how you said it does make sense. This is where I am confusing myself... not saying that she IS - but this mare(grulla) COULD (hypothetically) be homozygous - despite the fact that both her dam and sire were not. I think that is what was throwing me off - or I am just having a cloudy stupid day. THANKS so much for pulling my head out! hahahah

I didn't know about the OLWS though. Thanks for clearing that up as well. Another stupid question maybe... why do they put on the test results N/O when it is Oo?

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Morgan
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Re: Some genes I am confused about - homozygousity & OLWS

I borrowed an image via google :lol:
IMAGE(http://www.anselm.edu/homepage/jpitocch/genbio/locus.JPG)

A gene locus (or gene for short) is the section of dna that codes for a trait, since there are two strands of dna there is one "letter" on each strand at each locus known as alleles. It's what these alleles are that determines the color. A dominant allele is denoted by a capital letter and the horse only needs one of them to express that color. Recessive is with a lowercase and they need both alleles the same to be that color.
The extension gene locus codes every horse for a red or black base color (which is further modified by all the other genes). E is the black allele and is dominant to e, the red. ee is a red (chestnut) horse, Ee is a black horse that carries the red allele, and EE is a homozygous black horse.
When they reproduce they only pass on ONE of these alleles, one from each parent makes two for the foal. So, basically any time you breed two black horsse together you have a chance that the foal will recieve the black allele from each and be homozygous. Then when the horse is homozygous (EE) he will only pass on an E and so all foals are Ee or EE.
"She is not homozygous obviously because she has a red dun full sister."
not true :)
All that the red based sister means is that both parents had an "e", if they were black based and each Ee, then there is a 25% chance that your mare is homozygous (EE), however if one of the parents is red based a horse cannot be homozygous (ee only passes on an e, therefore all foals are Ee or ee.)
There are a few genes that are slightly more complicated (cream is incomplete, one cream allele dilutes red pigment and makes palominos and buckskins, while two makes double dilutes).

LWO is the same gene as frame overo, exactly the same. Visually though a Sabino or a Sabino and Splashed White can mimic a framelike pattern and test negative. Once they test negative though you should no longer call them frame overos.

accphotography
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Re: Some genes I am confused about - homozygousity & OLWS

N/O and Oo are the same. I think N/O is just less confusing for genetics newbies.

This statement is what confused you:

She is not homozygous obviously because she has a red dun full sister.

That's not true and I didn't catch it before. Her red dun full sister means her PARENTS can't be homozygous, but does not mean she can't be. As long as both parents are black based she could be. You should test her.

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accphotography
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Re: Some genes I am confused about - homozygousity & OLWS

Oh yeah... I knew I was forgetting something. All frame overos are LWO+ and all LWO+ are frame overos because they are one and the same gene. There are patterns that can mimic frame to some extent (not very well IMO) but it's rare.

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Re: Some genes I am confused about - homozygousity & OLWS

why do they put on the test results N/O when it is Oo?

because they feel like it :lol: actually I think they are just saying that they found the Frame allele and the other was negative (ie, not the Frame allele). Oo is more correct when dealing with the genetics though.

Shawneen
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Re: Some genes I am confused about - homozygousity & OLWS

LOL thanks

I was under the impression that all frames were not lethal, but thanks for clearing that up. Now that I feel like a dumb _ _ _ I will return to the hole from which I came! LOL

@ the homozygous - yes I was confusing myself. I knew that each parent passed on one, but I was not putting it together properly I guess.

ooooooo I shall post a pic of my mom's mare. Let's see if you guys can tell what she is...
No other markings other than flecks you see on her hip, her face and her socks. Blue eye(s) - can't remember if it's one or both - no matter. Baby had blue eyes, she was bred to a tobiano obviously.
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Re: Some genes I am confused about - homozygousity & OLWS

Definitely test this mare. I have a feeling she is frame (I can make a case for splash and sabino too, woo!)

Don't feel stupid! We all had to learn this at some point!

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Re: Some genes I am confused about - homozygousity & OLWS

Oh, and before Rabbit wakes up I have to tell you that she will post her usual rant about the word "overo". ;)

Although splash, sabino and frame can mimic each other and have been lumped together by many under the umbrella term overo, it is not entirely accurate. Especially since one is homozygous lethal and the other two are not, we try to separate them out from each other and even list each one separately when describing a horse with multiple patterns.

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Shawneen
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Re: Some genes I am confused about - homozygousity & OLWS

LOL well in the APHA world I can only call them Overo. "I'd like to register my frame/splash/sabino horse please!"
hahahaha
It's all good - rant away!

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accphotography
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Re: Some genes I am confused about - homozygousity & OLWS

I stroooooongly feel both dam and foal are frame. I also suspect splash and sabino. So ditto Sara.

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horsegen
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Re: Some genes I am confused about - homozygousity & OLWS

Just to add...

We use N/O instead of Oo because we (as geneticists) are technically testing for the DISEASE, not the color, even though they are the same thing. When we test for colors, we use upper and lowercase (Aa, Ee, etc.) if they are a simple dominant and recessive, but in disease tests N is used for "normal" and the other letter is used for the disease allele. H for HYPP, for example...a heterozygote is H/N. So OLWS (which is the name for the disease) is N/O. Technically, we test for the disease because that's what we mapped...we found OLWS by testing horses as carriers of "whatever" was causing lethal white foals. When we found the mutation, it was marketed as a disease test. We do that instead of saying we're testing for "frame" because frame is more subjective in its phenotype, and I think, because it drives home the point to breeders more that this is a disease they should be trying to avoid. Even though we know that frame and OLWS are the same mutation, we mapped it as the disease. Confusing, I know... :roll:

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Re: Some genes I am confused about - homozygousity & OLWS

Can you explain what you see to educate me further?
I will give you my interp...
-The flecks on her hip and the edge around her face markings could possibly be sabino.
-The blue eyes will be either splash or frame.
-Splash also causes high stockings, as does tobiano (on the baby).
-She doesn't have body markings so I don't see what could be obviously frame about her other than the blue eye(s), although solid Paints can still carry it.

-Baby is Tovero - though I know we don't like that term! hahahaha I have some yearling pics of him somewhere but I would have to dig them up off my hard drive and too much of a pain to get it out at the moment.

Ok what have I forgot or what do I have wrong. School me!!!

Horse gen that makes perfect sense and thanks for that info!

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Re: Some genes I am confused about - homozygousity & OLWS

The extensive face white and two solid legs are what make me think frame... and that hip marking is in kind of a weird place to be sabino alone. My guess is that it's a little white frame marking that sabino grabbed onto and made lacy.

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Shawneen
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Re: Some genes I am confused about - homozygousity & OLWS

Does a frame "spot" have to have pink skin? Her hip "spot" does not.

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accphotography
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Re: Some genes I am confused about - homozygousity & OLWS

The hip spot looks very strange to me. Like an injury or a mismark.

It's the very top heavy face white that screams frame to me. That and that much face white on the mare with so little leg white implies frame over splash.

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Re: Some genes I am confused about - homozygousity & OLWS

I see frame in the mare too. The hip marking is just in a wierd place in general, obviously not a splash marking and imo rather too high for the level of leg white to be sabino alone (I'd expect it to be more ventral), that leaves you with frame which is known for markings on the side.
Then there's the face, this is going to be hard to descride....first the blue eyes mean splash and/or frame so we have that down. Now splash tends to make a bottom heavy face marking that is skewed to one side, this one IS bottom heavy but I can't see the other side of the face and there's something else: spalsh marking ime run up and down the face (like any hooks on the white will point toward the eye and ear) on frame its more horizontal like this mare, if that makes sense? So I see more evidence of frame than I so of splash, which does not mean splash isn't there too, but mainly frame and sabino, judging by looks. And the foal kind of confirms my guess by having a top heavy bald face.

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Re: Some genes I am confused about - homozygousity & OLWS

Does a frame "spot" have to have pink skin? Her hip "spot" does not.

no spots have to have pink skin :)

Shawneen
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Re: Some genes I am confused about - homozygousity & OLWS

Just for the heck of it
This is the only other pic I have of her already loaded, but it shows the other side of her face.

IMAGE(http://www.brokenspade.com/snickers.JPG)

I see she has a little white under her jaw and it appears that she may have a white area on her neck, maybe its nothing - but I don't remember that being there. I could just be forgetting - getting old sucks.

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Re: Some genes I am confused about - homozygousity & OLWS

Um YEAH you could say that "falls off one side". :rofl

And yes, I'm reasonably sure that's a small white spot on her neck and that would absolutely 100% convince me of frame.

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Re: Some genes I am confused about - homozygousity & OLWS

So we think frame spalsh and possibly sabino?

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Re: Some genes I am confused about - homozygousity & OLWS

Yup, that's what I think. *nods*

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Re: Some genes I am confused about - homozygousity & OLWS

You guys are awesome! Thanks for all the info - It is almost 6am here now so I am off to bed. See you all later!

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Re: Some genes I am confused about - homozygousity & OLWS

oh umm wow, yeah, now I'm thinking frame AND splash too and I'm pretty sure that white chin is a giveaway for sabino. That much white on one side of the face along with higher hind socks with one higher than the other is almost certainly splash.

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Re: Some genes I am confused about - homozygousity & OLWS

I missed your comment about the white under her jaw... and just noticed that it's not just your eyes. I see it too.

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NZ Appaloosas
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Re: Some genes I am confused about - homozygousity & OLWS

LOL thanks

I was under the impression that all frames were not lethal, but thanks for clearing that up. Now that I feel like a dumb _ _ _ I will return to the hole from which I came! LOL

@ the homozygous - yes I was confusing myself. I knew that each parent passed on one, but I was not putting it together properly I guess.

First off, there is no such thing as stupid questions, except those not asked...secondly, no crawling back into holes is allowed here... :booty :laugh1

Additionally, all adult frames are non-lethal, in themselves, as OLWS foals are usually put down within a week of birth, due to defects in the intestinal tract...MonsterPony or others can give better details since this is something I've not totally immersed myself.

Another thing to remember, whenever two horses who are heterozygous (single copy) for any particular trait are bred together, there is only a 25% chance of producing a foal that is homozygous that trait. Heterozygosity has the greatest chance of being inherited, and 25% chance of the trait not being passed on at all.

Diane

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Re: Some genes I am confused about - homozygousity & OLWS

Hallo!!! :rofl
Just a word of caution here...
Most, in fact almost all, Tobianos carry another pattern.
If that pattern just happens to be Frame, and the owner has not tested the stallion because Hey, he's a Tobiano!!, then it you and ultimately your mare, or at least the foal, who will pay the price for this "Equine Russian Roulette".
ALL Pintos should be tested for LWO before breeding.
Someone saying an animal is a pattern does not make it exclusively that pattern.
The foal might not be a "tovero" (and yes, I do loathe that useless pointless word) it might not have any Tobiano at all, it is just a visual pattern with no testing to back it up, which is why I loathe the pointless useless stupid word :laugh1
Breeding a Tobiano to a horse with another pattern does not automatically result in a "tovero" the foal could just be Splash/Sabino/Frame....which by your thinking would make it an "overo"???

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Re: Some genes I am confused about - homozygousity & OLWS

LOL HI rabbit! I was waiting for you LOL

I completely understand what your are saying - like I said though in APHA terms, you have only so many choices.
I am sure you know how the registration works - and they do not require the tobianos or overos to be tested in order to register them. I was thinking about the tobianos carrying OLWS yesterday after I got off work. The exact thing you were saying - they could carry it too. As far as registration goes it is purely by eye. If they have the tobiano traits with no visible overo traits that is what they are registered as, same as toveros and overos. Seems to me that APHA needs to hunker down and change some things around a bit?? That exact thing was told to me about my mare I tested + for OLWS. "Just breed her to a tobiano" That's what got me thinking - if a solid Paint can still carry it why couldn't a tobiano as well.

Let's all mass email APHA :)

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Re: Some genes I am confused about - homozygousity & OLWS

I don't mean to hijack this thread, but Horsegen, regarding the O/n vs Oo being due to it being a test for a disease... I've seen het silver listed as Zn. Is that "wrong" then, and proper "terminology" should be Zz? Just curious :) Should the n be capitlized, lower case, or does it matter? Just want to write/type it properly :)

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Re: Some genes I am confused about - homozygousity & OLWS

Hey Chey! Glad to see you are here - I am sure there are others from "over there" here as well?

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