Finally, Example #1

[Olga]

From "Keeping a Family Cow" suppose we have this type of mating...
Sire: SGF LPFK Antares, tested red.
Dam: registered dun, don't know if she's been tested.
Question: is the calf red or dun?

So, looking at Antares' pedigree, we find out that

• his sire was dun
  
• his dam was black
  

It is important to look at Antares' dam's pedigree because we find that her parents were one red and the other dun, and her being black means she must carry one hidden red gene and one hidden dun gene. Which in turn for her to produce a red calf when mated with a dun bull, that dun bull would have to carry one hidden red gene.

So, if my logic is correct:

• Antares' dun sire is B/r d/d
  
• Antares' black dam is B/r B/d
  
• Antares (red) is r/r [B/d or d/d)
  

A dun color make-up can be B/B d/d or B/r d/d. When graphing the probability with two different versions of Antares' make-up, I get:

• 50% black, 50% dun
  
• 25% black, 50 % red, 25% dun
  
• 100% dun
  
• 50% dun, 50% red
  

*in all instances "r" stands for either of the red color genes.

So, please check my logic, correct any mistakes, and prove me wrong if I am.
Conclusion for me is that there is enough possibility that the calf is red for the expense of testing, jmo.

[Olga]

Well, I happened to look on the ADCA AI bulls page and Antares is listed red/red dun/dun, so I guess I wasn't off in my logic.
That limits his offspring to all dun when bred to a dun cow that does not carry red or to 50/50 when bred to a dun cow that does carry red.

[liz]

Olga he couldn't have be r/r B/d because black is located at the same locus as red and then he would appear black because red is recessive. Dun is in another location. Liz

[Olga]

Liz, I'm just following the ADCA article on colors here. They say that there are two pairs of genes that define color. The first pair is Black vs. Red, with Black/Black, Black/Some Kind of Red, and Some Kind of Red/Some Kind of Red combinations.
The second pair is Black vs. Dun, with Black/Black, Black/Dun, and Dun/Dun. So every animal would have a genotype composed of two pairs. I posted genotypes of Red Animals in the previous topic, and the Red/Red Black/dun is in there. I may have confused a few people by not using the letter designations they used in the article and on the genetic papers though. They use "E(dominant)" for black on the red locus, "E+" and "e" for red; and "B" for black on the dun locus, and "b" for dun.

[liz]

Hi Olga; The first locus is where black/red or wild red exist and the second locus is where dun exists or 'nothing'. So a red animal is either rr dd or rr nd or rr nn and the same combos with wild red. What article are you looking at? Liz

[gene]

liz,
maybe i have read everything all wrong all this time but i was of the opinion like olga. the first location was red or black, and the second was black or dun. thats how i interpretted the gene details that i read.


gene

[Olga]

I'm using the information about Dexter color genetics that appeared in the 2007 ADCA Membership Directory, pp. 88-92.

[liz]

What I understand from reading the Article about mapping the TRP1 (dun) gene on the Dexinfo web site is that dun is located at chromosome 8 and red and black are located at chromosome 18. Further to that I have a copy of an email from Carol Davidson explaining that red and black (and wild) are located on one locus and that dun is located, if at all, on another locus . The gene that causes a Dexter to be 'dun', TRP1, is not really a colour but rather a 'dillution' gene, that if homozygous, works on the production of the colour black but has no effect on the production of the colour red. It does make sense though that black could not be anywhere in a red cow since we know that red is recessive to black. Guys I am no geneticist and really someone with more knowledge than me should jump in here. Liz

[Olga]

Theoretically, it does sound logical. I was wondering that myself. How come, if Black is dominant, an animal can be red if it's double red on one pair and black on the other?...

But! Holes in DNA do not exist. I have no problem calling dun not a "gene for brown color", but a "diluted black" or a "modifier". But, yet again, since we don't have holes in DNA, it has to have a pair. It can be two diluted black genes, or a one diluted gene and something else, or two of those "something else". In the article in the Dexter membership book, they were referring to that "something else" as black.

Oh, and forgot, I agree completely, we need someone like CD to clear this up.

[liz]

Hi Olga; Of course I agree there can't be a hole in the dna but I think that the problem might be that we are thinking of it as a 'colour' and really I think that TRP1 is a mutation of the genes at chromosome 8. But as I say that is my 'lay' person interpretation. The one thing I am pretty sure about is that it is not black. I am going to copy the forwarded email from Carol Davidson re colour genetics below.

black and red and wild are on the same locus, so you can have black/black, black/red, black/wild, red/wild, or red/red or wild/wild. Both red and wild are red in Dexters. Both reds come out the same colour, so it doesm't really matter which you have, the appearance will be the same. Black is dominant to both reds.

Dun is on a separate locus, so at that locus you can have brown or null, (sort of void; it doesn't do anything). Brown is recessive BUT when homo, overrides black to give us the dun colour. BUT< BUT for some reason it doesn't affect either red, so if the animal is genetically homo for red and homo for brown it will still be red. Go figure.

Locus 1: base coat colour: B -black, r - red, w - wild; Locus 2 brown colour b- brown, n- null

BB nn = black
BB nb = black
BB bb = dun

Br nn = black
Br nb = black
Br bb = dun

Bw nn = black
Bw nb = black
Bw bb = dun

rr nn = red
rr nb = red
rr bb = red

rw nn = red
rw nb = red
rw bb= red

ww nn = red
ww nb = red
ww bb = red

So you can see that the ONLY time you get dun is when you have an animal that would have been black (homo or carring one of the reds) AND homo for brown. If it was only hetero for brown, the brown is not expressed because it's recessive.

That was the email. Liz

[Olga]

That makes sense. I hope they revise the color article in the future, because if this info is correct, saying "black" instead of "null" is confusing. Thank you for forwarding this info, Liz.

[liz]

No problem Olga; It really helped me make sense of it. Liz

ps www.dex-info.net/index.htm this is the link to 'dexinfo' where you can find Carol's paper or summary of the paper written about the TRP1 gene being responsible for Dun in Dexters. If you are interested go to 'articles' and then 'summaries' and you will find it there.

[liz]

Hi guys; If you go to dextercattleforsale.co.uk discussion board and click on the 'red colour' thread, Carol has written the same chart as above to settle a question about colour genetics (red specifically) in Dexters. L

[liz]

www.dextercattleforsale.co.uk go to 'discussion board' and then click on the 'topics' and go to the thread on ' red colour' L