explain homozygous dun, please

[copperhead]

I got the test results from my little dun bull, and as expected, he is a carrier. The paper also said he was "homozygous dun" . I didn't ask for a dun factor test, but, I guess they did one. Does that mean he'll only throw dun calves ??

P.J.

[J & M Chambers]

Hello P.J.

I believe all the "homozygous dun" is telling you is that your bull is dun. I don't think you can have a dun animal that is "heterozygous dun" as it would be black. The dun is recessive to the black at the Brown locus. So your bull at the black locus is b/b, not B/B or B/b. If you breed your bull to a black cow you could have a black animal - depends on what the black cow has and what half of the gene she imparts.... There is a good explanation of this somewhere in the ADCA 2007 membership directory.

I think I'm saying this correctly but I'm sure it will be corrected soon if I am not.

[anthony]

For the most part yeah.. Of course, it could have been a red animal that is also homozygous Dun as those animals show up as reds.. But beyond that, yeah, your bull would likely throw a black calf out of a black cow.. AT best you would have a 50% chance of a dun calf out of a black cow that was hetero dun..

[legendrockranch]

Wow! is that you Jeff?

This forum is starting to feel like home.

Barb

[copperhead]

OK, thanks all........I just don't understand all the herto, homo, and big and little b's I'm sure glad some of you do !!!
You're right Barb, this is the most activity I've seen on this board, and I'm sure glad. thanks again,
P.J.

[liz]

Ok let's see if I can give it a go at explaining....! All of you scientists out there, please keep your laughter to a silent roar!

There are two sets of colour locus, each with two colours attached in the Dexter. The first one is for black or red and the second locus is for dun or nothing. Black is dominant so a black animal can be homozygous (2 blacks) or heterozygous (one black and one red) at that location and still "look" black, but carry red. Dun is carried on the other locus and if an animal has only one dun gene, heterozygous, it will still 'look' black but carry dun, if the animal has 2 dun genes, homozygous, and at least one black gene on the other locus, then the animal will look dun. If the animal is homozygous for red, 2 reds, then it would still have two dun or one dun gene but it will look red and carry dun.
The reason for this is that dun works to prevent the black from totally forming and so without a black gene it isn't expressed. If you mate your dun bull to a dun cow you will get dun or possibly red if they both carry one red gene and pass it to the calf. You will not get black, even though both have to carry at least one black gene, because they will both pass a dun gene and that homozygous dun will stop the black from completely forming.
This is why a red bred to a dun will almost certainly get a black because the dun carries at least one black gene and unless it passes a red that it is carrying then the black will be expressed. Red to Red is the only colour that breeds true. Clear as mud? There is a good summary of an article on the dex-info site that explains the dun gene in dexters.....much more scientifically than me!!

[Cloverbell]

"Red to Red is the only colour that breeds true."

Wait, doesn't dun to dun get dun too?

Linda

[liz]

Yes but dun to dun could also produce red if both parents carried red and passed the gene. The dun would not be able to work it's 'magic' because it would need one parent to pass a black gene.

Also there is of course the wild gene but it is red but it works like the red and so why confuse things......haha!

[copperhead]

wow, very good liz.........
Linda, if I'm understanding Liz, the dun to dun will get dun, because the dun gene cancels out the black. This is so cool, I"m learning something.........

[Cloverbell]

Oh yes, of course. I forgot about that combo - I have a dun bull that carries red so I can see that happening at some point I suppose.