What we don't know about color

[kansasdexters]

Genebo,

Whenever I have an animal that has a test report that doesn't make sense, I have that animal retested at another lab to confirm or verify the original test report. Lab techs can make mistakes, even at the best labs. If I had a Dexter with red highlights, that came from a Dexter that was known to carry red, I would retest that animal if the original test indicated ED/ED, B/B. The original test might be wrong.

Patti

[Cascade Meadows Farm - Kirk]

Melanocytes are the cells of the body that produce pigment called melanin. Melanocytes produce two chemically distinct types of melanin pigments: eumelanin (black and brown) and pheomelanin (red and yellow). White is the lack of any pigment.

Many different genes impact how the melanocytes produce eulmelanin and pheomelanin. For example, the Brown gene at the Brown locus, is a mutation that interferes with the normal production of black pigment, and makes the black pigment appear brown (dun).

The genes found at one particular location (locus) on the chromosomes, control the EXTENT of production of the 2 pigments. This locus is called the Extension Locus.

The wild-type gene (original gene found in wild ancestors) at the extension locus is coded as E+ (E = Extension locus, + = wild-type). The original E+ gene allowed the animal to produce a balanced blend of red and black pigments. Other genes found at other loci (plural for locus), control the amount of pheomelanin vs. eulmelanin produced at each location on the body. Original cattle had patterns of red and black pigments, the way many wild animals today have various coat patterns.

In dexters, we refer to E+ as a form of red, but that's not really true. E+ = the ability to have a blended mix of red and black pigments. So E+ animals can look very black or very brown, or very red or somewhere in-between.

The original E+ gene has two primary mutations: ED (black) and e (true red).

"ED" instructs the melanocytes to produce a TON of eumelanin pigment, overwhelming most of the pheomelanin pigment. But the pheomelanin (red) pigment is still produced (more or less in some parts of the body). A little red can show through the black in some areas of the body, and that may depend on other genes at other locations.

"e" inhibits the production of MOST (but not all) eumelanin (black) pigment (more, or less in some parts of the body).

Understanding this, explains why black animals can still show tinges of red in places, and explains why true red (e) animals can show tinges of black pigment in some places.

[dexterfarm]

I have no red in any of mine just black and dunn. some of the ones that carry dunn have the same high lights that Gene is describing tail legs and ears. It is not vary noticeable. You could say it might be sun fade but if it is its the same dexters in the same spot every year. Not all of mine that carry dunn have the highlights some are coal black every where.

[Cascade Meadows Farm - Kirk]

Dec 29, 2012 16:23:15 GMT -5 @genebo said:

Patti,

Her top coat was heavy, straight and coal black, her undercoat was thin, curly and red. In winter, her undercoat would get thicker and she would look red in some light.

When I say "pure black", I mean Ed/Ed B/B. According to common usage, this means that the Dexter does not carry either red or dun, and will always breed true for color.

How else do you explain the white color that shows up in one of our 3 solid colored animals? Is there a white gene? We've all come to accept that brindling is present in our breed's makeup and is not caused by either of the two commonly tested genes. It may be enabled by E+, but is not caused by E+. Just like dun is not caused by Ed, but is enabled by Ed.

Again, ED/ED black animals can still produce plenty of red (pheomelanin) pigment, but the red just gets overwhelmed by a large amount of black. Black (eumelanin) pigment is VERY dense and typically just covers up the much weaker red which is produced in most all animals except white animals which have no pigment at all in their white areas.

Many of the lessor known color genes are already known, but we just don't have much experience with them in Dexters.

Br = the brindle locus

Sp = the spotting locus with a good number of different alleles that cause the complete absence of pigment in certain locations on the body. White is simply the absence of pigment. Non-spotted is dominant over spotting. Herefords are homozygous for their particular famous spotting alleles at the Sp locus. There are likely a good number of different spotting alleles that can interact with each other to form all sorts of spotting patterns. Since spotting genes are recessive to the dominant non-spotting gene, then spotting can hide for many generations. Since we select AGAINST spotting in dexters, the recessive spotting gene frequency is quite low.

Agouti = a primary patterning locus. This likely controls the various patterns of black and red we often see in E+ animals (but not the brindle pattern, which is its own separate locus). We don't pay too much attention to Agouti in solid colored cattle, but it is important in patterned cattle.

ED, E+, and e (true red) dexters can all have "Dun" (brown) coloration, but we only see it vividly in the ED animals. The dun color is Eumelanin pigment that hasn't catalyzed properly because of two "broken" copies of the TYRP1 gene at the B Locus. The lack of catalyzation leaves the black pigment looking brown.

E+ animals can have a lot of Eumelanin (black) pigment, and if they also have two "Dun" genes, then the black hairs will be dun. So indeed, you can have a dexter that is both red and dun at the same time (but we would just call it a "red").

To imagine what a red and dun dexter would look like, look at an obvious E+ wild red Dexter like the VERY fine Cornahir Outlaw with much black highlights, and imagine what he would look like if his black hairs were dun instead of black.



e/e true red animals can also have a little Eumelanin (black) pigment in some limited spots on the nose, ears, and tail switch, and if they also have two "Dun" genes, then the black will be brown (dun) colored. But you'd likely not notice the dun hairs among all the red hair.



PS. We have Icelandic sheep on our farm and they have a dizzying array of colors and patterns and forms of white spotting. If you don't understand the genetics, you'd be overwhelmed by it all. But with a good understanding, it's very predictable. Most of the color and pattern genes have a large amount of commonality among most all mammals. Black, Yellow, and Chocolate Lab dogs are equivalent to black, red, and dun dexters (with pretty much the same genes controlling the colors). "Dun" is called "Chocolate" in Lab dogs.