dun

[Rutherford]

I have lived long enough to know you never finish learning! Wouldn’t that result in dun brindles as well? I guess it will be some time before DNA gives us all the answers

Beryl (Woodmagic)

[Kirk- Cascade Herd US]

I have lived long enough to know you never finish learning! Wouldn’t that result in dun brindles as well? I guess it will be some time before DNA gives us all the answers

Beryl (Woodmagic)

Yes! The brindle gene (dominant Br) at the Brindle locus is a pattern gene that only works in the presence of the E+ gene at the E locus. The E+ gene provides the two pigments (red and black) necessary to make a pattern and the Brindle gene provides the specific brindle pattern instructions. Now if you add in two recessive genes at the B (Brown) locus (called "dun" in Dexters, or called "chocolate" in dogs, then the black becomes dun and you would then have a dun-brindle. There are also chocolate-brindles in dogs with the same genetics.

Now red with brown stripes is going to be much more subtle than red with black stripes, so it might be harder to see. Further, there are likely many other minor genes at other locations that affect the degree of brindling.

Kirk



Edited By Kirk- Cascade Herd US on 1198014746

[Rutherford]

Where I have come across a ‘dun’ Dexter with Jersey in the pedigree, the result has never been a brindle, but a ‘dun’ which is a very poor relation of the true Dexter dun, being often very washed out and pale. Incidentally, I understood it had been established that the dun gene in the Dexter was specific to the Dexter alone.

[Kirk- Cascade Herd US]

Where I have come across a ‘dun’ Dexter with Jersey in the pedigree, the result has never been a brindle, but a ‘dun’ which is a very poor relation of the true Dexter dun, being often very washed out and pale. Incidentally, I understood it had been established that the dun gene in the Dexter was specific to the Dexter alone.

The two pigments, Eumelanin (black/brown) and Phaeomelanin (red/yellow/orange) are common to mammal species. In order to create full black pigment, a particular protein is required to complete the process. This protein is called TYRP1 and it stands for "Tyrosinase-related protein-1". All breeds of cattle have the dominant (normal) gene for TYRP1 which allows for normal and complete production of black pigment (in those animals that are coded for black pigment - those with ED (black) or E+ (mix of red and black) at the E locus).

The gene locus (locus=location on the DNA) that codes for the TYRP1 protein is called the Brown locus, but it probably should be called the Black locus because its normal dominant function is to help complete the creation of the color black, and only a defective version results in the color brown.

In many breeds of mammals, a DNA copy error (mutation) very rarely occurs, resulting in a recessive defective gene version (allele) at the B locus that disables the TYRP1 protein and results in any would-be black parts of the animal being brown instead of black. The normal gene at the B locus is usually coded as BB (dominant black) and the defective recessive as Bb (recessive brown).

To date, in Cattle, this rare defect mutation has only been found in the Dexter breed, but it is commonly found in many other breeds of other species. Chocolate colored dogs are brownish colored exactly for the same reason that the dun Dexters are brownish colored (defective TYRP1).

My theory is that this defect mutation has almost certainly popped up in other breeds of cattle but has likely remained hidden, gone unnoticed, or has been culled. It would only stand out in solid black breeds of cattle. For example, imagine a Black Angus herd with the occasional red calf. They have the mindset to cull anything that isn't black so any very rare brown/dun calves would simply be culled. In true red breeds, like Red Angus, the defective gene wouldn't exhibit at all, so would go completely unnoticed.

Concerning washed-out duns in animals with Jersey backgrounds, I can think of three possibilities and I'll list them in the order I believe they would be most likely:

1. We can be tricked into drawing false conclusions from too little data, casually collected. For example: "It always rains when I wash my car, therefore, washing a car makes it rain". It's possible that washed-out duns occur randomly due to the effect of other genes and/or environmental impacts but have coincidently occurred in some animals with Jersey outcrosses which tricks us into drawing a (perhaps) false conclusion that the genes come from the Jersey line. A scientific study would be required to get to the bottom of this.

2. A wild-type red (E+) with much black shading that also has two dun genes Bb/Bb, can be red with dun shading instead of red with black shading. Perhaps this is the cause and if so, perhaps the E+ from the Jersey is the culprit.

3. Many little understood secondary genes can affect the tone or shade of a color. It's possible that one or more of these toning genes either came from the Jerseys or came from the line of Dexters that was used in crossing with Jerseys. I put this likelihood as small because any genes from remote outcrossings are almost certainly lost within 5-6 generations unless they are specifically selected for.

So, by far, I would lean toward option 1 (I never trust any conclusions, especially my own, that are based on casual, unscientific observations).

Kirk