Basic Concepts of Dexter Color Genetics

[Olga]

• Dexter cattle occur in three distinct colors: black, red, and dun. Two pairs of genes that are located on separate chromosomes control these colors.
  
• Black and red is one pair of alternative colors. In Dexter cattle, there are two different red genes. The two red genes are alternatives to each othere, and they are not visually distinguishable. However, they are distinguishable by a DNA test. Both red genes are recessive to their black alternative. This means that every red Dexter contains two red genes, one inherited from its sire and one inherited from its dam.
  
• Black and dun is another pair of alternative colors. The dun color in Dexters is due to a brown mutation, and it is recessive to its black alternative. This means that every dun Dexter contains two dun genes, one inherited from its sire and one inherited from its dam.
  
• Two black Dexters can produce black, red, or dun calves. In order for two black parents to produce a red calf, each parent must carry a hidden red gene. In order for two black parents to produce a dun calf, each parent must carry a hidden dun gene.
  
• In Dexter cattle red is the only color that breeds true. Two red Dexters can produce only red calves even if each parent carries a hidden dun gene. A Dexter that contains two red genes and two dun genes is red in appearance.
  
• If a red Dexter that has two dun (Yup, this is where I typed up "dung" instead) genes is crossed with a dun Dexter that does not carry a red gene, ther result will be a dun calf. Each dun calf resulting from this cross will carry a hidden red gene.
  
• Two dun Dexters can produce dun or red calves. In order for two dun parents to produce a red calf, each parent must carry a hidden red gene. Every red calf that is produced by two dun parents will have two dun genes.
  
• When a red Dexter that does not carry a dun gene is crossed with a dun Dexter that does not carry a red gene, the result will be a black calf. Each black calf resulting from this cross will carry a hidden red gene and a hidden dun gene.
  
• A colored Dexter calf must be red if its sire or dam is known not to carry dun. Conversely, a colored Dexter calf must be dun if its sire or dam is known not to carry red.
  
• Additional genes, independent of the genes for the baisc colors, may be present in an animal's genotype and may modify the appearance of the animal. Such genes include but are not limited to those which are responsible for brindling, black noses in reds, black shading in reds, and the shade of color of reds and duns. Modifier genes do not alter the principles contained in the preceding nine concepts.
  

This text is typed as it appeares on page 88 of the 2007 ADCA Membership Directory.

[Steve]

Thanks, Olga. It will be nice to have this link to return to when necessary. Short, concise, and easy to read. Just the way I like things.

[Wags]

Thanks, I have been trying to figure out how to get a red or dun calf out of my black girls.

[marion]

Thanks for posting this Olga! I must admit I had a little chuckle about the "dung" gene. I suspect all my cows carry it ;D ..marion

[ctownson]

The ADCA web site has some good articles detailing the color genetics of Dexters. Here is a link:

www.dextercattle.org/genetics.htm

[lindonestate]

I had to explain this to hubby, and a few others in here Oz, so here is my explanation, hopefully, in plain english........ ;D

The Dexter Genetic Colours

The black gene ED is dominant. If a Dexter has only one copy of ED, then it will appear black irrespective of what colour the other gene is.
If the Dexter has two copies of ED (one from each parent) then it will appear black.

There must be two copies of DUN (TYPR1/b) AND at least one copy of the black gene for a Dexter to appear dun.
This is because the TYPR1/b is a mutation causing a protein to develop which causes the dilution of the black colour only, making a Dexter appear dun. This protein will never dilute red.

If the Dexter has only one copy of TYPR1/b (dun) attached to one copy of black and the other black gene does not have TYPR1/b (dun) attached, then the Dexter will appear black, but will be a carrier of dun.

So technically ALL dun coloured Dexters ARE carriers of black.

Red Dexters CAN carry the TYPR1/b (dun) gene or even two copies of the TYPR1/b (dun) attached to each red gene, but because the protein will only dilute black, the Dexter will always appear red.

This is why the saying only two red Dexters will breed true. Meaning you know what colour the calf will be – red!

FYI – black and red colour share the same gene. So this gene will only ever be red or it is black.
There are always TWO copies of this gene, one from each parent.

TYPR1/b (dun) gene can attach itself to this gene whether it is a red or a black.

ED = Black
b = Dun
E+ = Wild red
e = True red

Black Dexters

ED/ED = black coloured only
ED/EDb = black coloured but dun carrier
ED/E+b = Black coloured but dun AND red carrier
ED/eb = black coloured but dun AND red carrier

Dun Dexters

EDb/EDb = dun coloured – but because there is also at least one copy of the black, duns are always black carriers
EDb/E+ = dun coloured but red AND black carrier
EDb/e = dun coloured but red AND black carrier

Red Dexters

E+/E+ = red coloured
E+/e = red coloured
e/e = red coloured
E+b/E+ = red coloured but capable of producing dun if mate has black gene + b given to progeny
E+b/E+b = red coloured but capable of producing dun if mate has black gene + b given to progeny
E+b/e = red coloured but capable of producing dun if mate has black gene + b given to progeny
eb/e = red coloured but capable of producing dun if mate has black gene + b given to progeny
eb/eb = red coloured but capable of producing dun if mate has black gene + b given to progeny

I think I have covered all possible genetic makeup for colours.

Colour testing of parents is the only way you can guarantee what colours are ‘possible’ in your calves. It’s a percentage game.
Even Reds can be either Wild red or True red, and then they could also be capable of producing dun depending on their mate’s genetic colour makeup.

[cddexter]

Hi Lindonstate

almost right. it IS complicated, isn't it.

DUN DEXTERS

EDb/EDb = dun coloured – but because there is also at least one copy of the black, duns are always black carriers
THIS IS CORRECT

EDb/E+ = dun coloured but red AND black carrier
You are missing the second 'b': IT SHOULD BE EDb/E+b

EDb/e = dun coloured but red AND black carrier
You are missing the second 'b': IT SHOULD BE Edb/eb

That's because Dexter brown is recessive, and MUST have both genes of the pair present to be phenotypically brown.

And, for Gene: originally Sheila did say it wasn't a dilute gene because all known dilutes were dominant. She approved the paper I presented on her behalf at the 2002 Congress in AU, where I referred to as either/or, and called it a brown gene not a dilute one. But if you read her full poster on the topic, she does refer to it as a dilute gene, but only in the sense that it changes black to brown and in fact refers to it both ways at the same time. Sheila predicted that a homo red/homo brown animal would be brown. John Potter thought the opposite. Just before Sheila's poster was presented in Germany (I think), John had a bright red calf born, double homo, and color tested it to confirm. Sheila changed her poster to reflect the correct solution. (John, with his breeding records and genetics background, provided the samples and pedigrees and photos, Sheila did the DNA work and related the results to her Dachshund brown study.)

I understand John is ill again, so I recommend not bothering him right now. However, his records are the most complete of all research into Dexter dun. He has found all sorts of modifiers, including the common ones like mealy nose, half red/half black hair (I saw this myself 20 years ago in Ireland in the Cornahir herd), dark faces, legs and tails, and various tones of cream in the tails.

What I find most interesting is how the E+ can vary in color between breeds, but is consistent within a breed. No one knows why. Genetics is such cool stuff, I love it. cheers, c.

[lindonestate]

Whoops - thanks for that. I knew what I meant ;D
Will edit my table now to make sure it is correct.

I love working this out, its so unusual and exciting

[geraldbharris]

that's seems to be interesting! really nice

[lindonestate]

Not a dilute gene? Then what is it that labs are testing?

The Dun coat color in Dexter cattle is a dilution of black pigment (eumelanin) caused by a recessive mutation in the gene tyrosinase related protein 1 (TYRP1), also known as the Brown locus. The hair color is diluted to shades of dark brown to golden. Red pigment is not diluted by this mutation. A genetic test specific for the Dexter Dun mutation is available

Several genes are involved in the process of creating the complex coat colors and patterns found in domestic cattle. One of these is the Melanocortin 1 Receptor (MC1R) gene, also called Extension, that controls the production of black (eumelanin) and red (phaeomelanin) pigments.

The three alleles (forms) of this gene are dominant black (ED), Wild type (E+) and recessive red (e).

Dominant black (ED) is dominant to the other two alleles and animals with this allele are jet black (solid or spotted).

The Wild type (E+) produces cattle with reddish brown to brownish black coloration with a tan muzzle ring.

Two copies of the recessive red (e) allele will result in red color.

The other coat color genes act as modifiers of these base colors adding white spotting patterns, reorganizing the distribution of red and black pigments (Brindle and Agouti) or diluting the pigments (Dun, Charolais dilution and Simmental diution).

(Extract from the tests performed at the Veterinary Genetics Laboratory
University of California, Davis) where us aussies have to send our tail hairs for Dun identification

So because the dun 'gene' is a modifier, Black will always dominant over it no matter what.

[cddexter]

Even ED/ED animals can have coloured tinges, especially up in the groin area.

E+ doesn't always give you mealy noses or dark reds. You can have regular coloured hair at the nose, and bright red bodies, too. I believe you only get the black nose or spotted nose with E+; pink noses are e.

You can get black points, like a horse, with e as well as with E+.

cheers, c.

[rhonda]

Have there been any studies on the different eye color in some of the Duns?

[midhilldexters]

Hi Carol,
would these 3 pics change your mind? These 3 animals are all e/e and have speckled noses.

[cddexter]

Hi carol K

Yup.

Now that we are getting so many reds in North America, I'm bound to be wrong somewhere along the way. My experience has mostly been in England. The Knotting reds were little e and a lot of them had really black points, but with pink noses. the third photo is heading in that direction, but Jaynes' were black right up to the eyes, and beyond.

I've seen duns and E+'s with spotted noses, but until now not little e's. Thanks.

Did you see Gene posted about a dun dexter with 'jersey' in the name, which made me wonder if it was a cross. Since all Jersey's are E+, and supposedly don't carry Dexter brown, it would be interesting to find out the color genetics of the animal...I'm thinking the color modifier must be dominant to get a brown animal, since our brown is recessive.
Post Modified: I see Gene posted the bull was already 3/4 Dexter and could have carried dun, so my guesses don't count. Too bad, it could have been interesting.

Do you think the assn would be interested in using some of the excess money they have in the bank for some dna work?

cheers, c.

[legendrockranch]

Carol K, looking at the nose colors on those animals I would have never expected e/e.