Dun filly - anyone know where I can find out if she is homozygous?

Question

My two-year old filly is absolutely DRIPPING with dun factor. I know you can send in tail/mane hairs to a DNA Lab (i.e. UC Davis) to check for red and black factor, the Agouti gene, the cream dilution, and the silver dilution, but there isn't a "test" (That I have found) to conclude if a horse is homozygous for the dun gene.

Is testing for the Agouti gene a way to figure it out? I'm so confused - can someone explain this to me? :(

Thank you!

Answer 1

Double S gave you the right site but here is the page you want start with.

http://www.animalgenetics.us/Equine.htm

I have looked and all I have been able to find out is that there is no testing available for homozygous dun. The dun gene is a dilution gene, but unlike the creme gene , it is not a dosage gene and doesn't always express itself like the creme gene.

Danelle, I think you should go and read info on duns at UC Davis and other genetic sites. Dun, silver and champagne do not express themselves in all colors like the creme gene.

Answer 2

http://www.animalgenetics.us/CCalculator...

Look in the tabs above the page.  

Answer 3

Here you go ^^...

http://www.grullablue.com/colors/homozyg...

The website states there is no current test available for homozygous dun gene :(

Answer 4

I disagree with Horsybill on the fact that the dun factor is not always expressed, it is alway expressed according to the information I have read over the past 5 years regarding color gentics.  

There may be other genes that are affecting the color along with the dun factor, such as bay, cream, and grey, howeve in all cases the dun factors still show through, although slightly altered due to the other genes.  Some associations may or may not recognize or distinquish all of the following combinations. A sorrel with the dun factor is a red dun, a bay with it is a bay dun, a palamino with the dun factor is a dunalino, a black with the dun factor is a grulla, a buckskin with it is sometimes refered to a line backed buckskin.

The Aqouti gene is the gene that produces a bay.    A bay is a black horse with the aqouti gene that limits the back color to the points, the lower legs, mane and tail.  A sorrel can carry a bay gene or be homozygous bay, its just not expessed as it is only works on black horses.

A black horse that has a dun gene would not look like a black, it would be a grulla, and yes a grulla could be homozygous dun and homozygous black if it came from a grulla to grulla mating, that does not mean however that every grulla grulla mating would produce a grulla.  If the parents are not homozygous for grulla, they their off spring are not guaranteed to be grulla or homozygous for grulla.  

After Horsybilly called me on my previous answer I went to the UC Davis site.

http://www.vgl.ucdavis.edu/services/coat...

and I found that he is misquoting the site.  Below you will find copy of text from their site.  The paragraphs are complete as taken from the site.  

It does not say that the dun gene is not expressed on all colors, it states:

"The basic colors can be diluted by at least four genes: Cream, Champagne, Dun and Silver. The Cream gene has a dosage effect in that a single copy of Cream produces palominos, buckskins and smoky blacks. Two doses of Cream produce cremellos, perlinos and smoky creams. Champagne, Dun and Silver do not show a dosage effect."

What is mean by dosage affect is that the Champagne, Dun and Silver genes do not get lighter when they are homozygous the way a cream does.  

Below is the information listed on their site in regards to duns.

"Gene D: Dun Pattern and Pigment Dilution

The D gene determines a second kind of dilution of coat color and its effects can be confused with those of Ccr. However, there are several important differences of the effects of D and Ccr on color. First, D dilutes both black and red pigment on the body, but does not dilute either pigment in the points. Red body color is diluted to a pinky-red, yellowish-red or yellow; black body color is diluted to a mouse-gray. Second, in addition to pigment dilution, a predominant characteristic of the allele D is the presence of a particular pattern which includes dark points, dorsal stripe (list), shoulder stripe and leg barring. Third, homozygosity for D does not produce extreme dilution to cream as does Ccr.

This pigment dilution pattern is called dun. In an otherwise red horse, the D allele produces a pinkish-red horse with darkened points known as a red dun or claybank dun (ww, gg, ee, CC, D). In an otherwise bay animal, the D allele produces a yellow or yellow-red animal with black points known as a buckskin dun (ww, gg, E, A, CC, D) (Fig. 2D). An otherwise black animal with the D dilution allele is a mouse gray color with black points known as a mouse dun or grulla (ww, gg, E, aa, CC, D).

The effect of D and Ccr can be easily confused in A, E horses so care must be taken in identification. It is possible for an animal to have both the Ccr and D dilutions, a situation which may be difficult to distinguish except by breeding tests.

D is found only in a few breeds of horses, and probably in the United States would only be seen in stock horse breeds, as well as in some ponies.

DD: Horse shows a diluted body color to pinkish-red, yellow-red, yellow or mouse gray and has dark points including dorsal stripe, shoulder stripe and leg barring.

Dd: Same as DD.

dd: Horse has undiluted coat color."

I hope this helps clarify the dun confusion that exists.

Thanks!

Danellej