homozygous ??

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lisaward

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a friend of mine has just brought a colt that is said to be tested to be homozygous,he is a black colt .

could this be true or does the horse have to be coloured as well as both his parents.
i have tried looking online but can't find anything
 
He could be homozygous black, which means he will only put in the black gene to his offspring, black is a recessive gene also. A chestnut can also be classed as homozygous has they have to have 2 chestnut genes to be chestnut, homozygous basically means they carry 2 of the same genes rather than one of one and one of another.
 
I was just away to say the same as HG on this one...........
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Black is dominant not recessive. But it can get diluted to bay by a seperate gene. Essentially all horse's are either black or red and then have other modifers that make them bay or coloured or spotted etc

If he is homozygous black it just means he doesn't carry the chestnut (red) gene.
 
Becaue I have a soft spot for black horses this is what I found last year;
The Agouti gene controls the distribution of black pigment. The dominant allele A restricts black pigment to the points of the horse (mane, tail, lower legs and ear rims), as seen, for example, in bays and buckskins. The recessive allele a uniformly distributes black pigment over the entire body.

Breeders interested in producing black horses need to have breeding stock carrying the a allele, in addition to the E allele of the Extension gene. Using results from the red factor and agouti tests, click here for a table of breeding schemes to produce black animals.

Test results are reported as:

A or Aa: Black pigment distributed in point pattern. The basic color of the horse will be bay or brown in the absence of other modifying genes. A has no effect on red pigment (ee).
a: Only recessive allele detected. Black pigment distributed uniformly. The basic color of the horse will be black in the absence of other modifying.
 
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Black is dominant not recessive

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Would you like to write to Jeanette Gower and tell her that because I'm sure she really needs correcting on that fact, especially after spending over 20 years researching the aspects of coat colour and inheritance in horses!
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She is adamant in her work that Black is the second most recessive colour after chestnut...
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tut tut naughty woman writing something sooooooo wrong
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I'm useless at this sort of thing, but from my understanding when I was doing some colour research, it all comes down to whether the horse is "e" or "E" doesn't it? The former being recessive and the latter being dominant?
 
In truth yes black can technically be dominant and recessive depending on as you say the E or e. In simple gentics (which is easiest to explain to anyone who isn't up on genetics) black as a colour is classed as recessive, and only chestnut is more recessive, its when you go further and deeper into genetics with all the agouti and intensifying...... etc etc it can be both but I find it unnecessary to go into such great detail, when most people are looking for just the simple answer to their colour genetic question, why confuse the issue, in my book keep it simple
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HG how can I guarantee a nice black foal next time from a liver chestnut mare? Will I need a stallion that is from black parents? Mind I think my daugher would rather have a Pally next time. Sorry hijacking this post.
 
Unless the liver chestnut has been tested to be homozygous reccessive agouti, you can not and will not guarantee a black foal.

If she is homozygous recessive agouti (aa) then use a stallion such as Stravinsky xx who is black, and homozygous black.

His genetic profile is aaEE, and you need a mare who is also aa (doesn't matter if she is EE, ee or Ee in this case).
 
Well he would be worth considering as already own a PB Trak so worth keeping up the membership. It wont be for a couple of years yet I will have to wait for the yearling to come under saddle before I will be permitted to cover Mo again.
 
Stravinsky is approved with virtually all of the big studbooks, but he is an old horse, so it's difficult to say how long he will be around!

I have two mares in foal to him this year - one is a homozygous coloured (who is also homozygous black), and the other is a chestnut. I've not had her tested, so I don't know if we will get black or bay from her.
 
It's not that difficult to test though - £16 and some hair, and you're away! The genetics of most colours are fairly simple - you just have to remember that it is two genes that control the three base coat colours.
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I really wont get away with putting her back in-foal next year. Anyway it will give me an idea of what attributes she contributes as this one grows up. He is turning into quiet a nice bay, though not a drk as I would like, Mo is going her nice drk liver for the winter.
 
I think everyone who has ever explained colour genetics to me must have oversimplified it by saying every horse was either E or e, and a or A was something that happened to the E. There are only 2 'colours' black or red, with black the dominant one. Everything else is a modifier (which is what I think Tia is saying). Which in my way of thinking makes black - E - dominant. Obviously agouti is dominant too, but that is something happening to the colour rather than a colour itself??? Or am I just being simple
 
He can be homozygous for black; yes. And that doesn't mean he should be coloured as then he would be homozygous for the tobiano gene.
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yes but he was told he guranttes coloured foals that why i am saying he should be coloured to throw those.
i didn't say he was homozygous black i just wondered if my friend was told he was homozygous and just asumed he threw coloured when he was only homozygous black

gosh hope that makes sense........
 
"All horses are homozygous for the B locus which gives black pigment (that is B+B+) , this is altered in horses that are not black by genes at other loci, especially the A and E series. The first alteration is produced by the allele At which changes the soft parts to lighter red or yellow, but keep the black coat over the body, thus creating a brown horse. The second alteration, brought about by the AA allele (that second A is suppose to be a little but still capital A), restricts the black pigment to the legs, mane, tail and ear tips. The horse will be bay. The most recessive allele, Aa, has no effect at, so as AaAa the horse remains black."

Its all as clear as mud to me!!
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I think it probably depend on who has taught you about genetics and which parts they have told you and which they scooted over, beyond A Level Biology, I am self taught from books and papers
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but I still say we are both correct technically
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But in answer to the OP question it is possible to have a homozygous black but he would have to be coloured to be able to throw coloured as the tobiano gene is dominant and therefore if they have the tobiano gene whether homozygous or hetrozygous they will have a coloured coat (just like Tia said)
 
Of course if he is black with four white legs and possibly a teeeny patch somewhere discreet, he could be a tobiano..

HG - Tell me about this "B" Locus. Sounds intriguing.

As I understand it (from study of genetics at A level and Degree level, and extensive research into coat colour genetics) there are three base coat colours (Black, Bay and Chestnut) which are controlled by two genes - Agouti and Extension.

Extension (E) determines whether the horse has got any black hairs at all. This is a dominant gene, so the horse only needs one copy to be able to produce black hair. The homozygote recessive (ee) will not have black hairs, and is therefore Chestnut. The heterozygote or the homozygote dominant (Ee or EE) will be have black hairs in their coat - eg will be either Black or Bay.

Agouti (A) controls the distribution of the black hairs. All horses, even those "ee" ones with no black hairs, will also have genes at this point on the chromosome. The dominant form of this gene (A) will restrict the black colour to the points of the horse - in terms of colour, this means that you wil have a Bay horse. Conversely, the recessive form (a) will allow an even distribution of black hairs around the whole of the horse - the horse will be Black. As agouti is dominant, you only need one copy, therefore homozygous agouti (AA) or heterozygotes (Aa) will be Bay. The recessive homozygote (aa) will be black.

In order to have a black or a bay horse, you must have at least one copy of the extension gene (E). The agouti gene will then determine whether you get black or bay. It really is quite simple to me - perhaps I have trouble explaining it in a way others find easy to comprehend!

The term "homozygous black" can be somewhat confusing though, as it is actually referring to the genes the horse has at the extension loci - ie whether it can produce black hairs or not. Genetically, homozygous black is EE, and is nothing to do with the agouti genes at all. I have 4 homozygous black mares, none of which are actually black themselves..
 
It was a quote ashbank (hence the " ") and like I said it was as clear as mud to me
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and I owned up to being self taught from reading books and papers beyond the A-Level stage. (I was really quite a dunce at school
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). I am quite happy to give you a list of references I have used and you can take any problems with their work up directly with the publishers....
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Sorry, it was a genuine question regarding which author had written that! I wasn't being snide or anything.. I think things have moved on somewhat in recent years, and I suspect that work was published a wee while ago.
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Hi. I was lead to believe that only a coloured could throw a coloured. Actually, Ihave had many discussions with someone who is very experienced in this field.......and she certainly put me in my place about it. The argument started off with me saying that a solid colour bred from a coloured parent stood more of a chance of producing a coloured foal if put back to a coloured.and she blew my theory right out of the water. we have since gone on to breed several arab/coloured ponies.after the advice from this woman.
 
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So considering I know nothing about the colour genes, how do you know if a combination will produce a black then..........do you have to test the mare and then go with the stallion??

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Unless both parents are tested, you've not much way of knowing. The way to guarantee it is to use a black mare and a black stallion (this eliminates the possibility of bay, but still leaves a 'risk' of chestnut). You can eliminate the chestnut by making sure that one of the parents is also homozygous black (which actually refers ot the extension gene, and could be better described as "homozygous not chestnut". Stravinsky is an example of a black horse who is homozygous black - if he is used on a black mare, you will be guaranteed a black foal.

*Other black, homozygous black, stallions are available*

Re coloureds - yes, at least one parent must be coloured to have a coloured foal.
 
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