Re: RC: greys and cancer

[CMKSAGEHIL@aol.com]

In a message dated Thu, 6 Sep 2001  4:43:08 PM Eastern Daylight Time, JUDYK89 writes:

> 
> I heard on another board, from some color guru's, that gray is not really a "color" but more of a genetic defect/mutation/trait.  So maybe this has something to do with the higher incidence of cancer?  Maybe someone with color background knows? 

Welllll, sort of.  If one gets down to the basics of color genetics, there are only two colors--black and red.  Black is dominant, red is recessive, and so both in terms of genetics and of the trait itself, red is the absence of black pigment.  Red is chestnut.  Black, with no modifying genes, is black.  In many breeds, there is a modifying gene called agouti that makes black pigment segregate to the points--mane, tail, legs, etc.--and this gene occurs in a very high frequency, so most horses that are genetically "black" become bays.  Grey is another modifier gene--regardless of whether the horse has a red or black base color, if he has the grey modifier, he will turn grey.  Likewise, there are various modifiers that make red horses turn dun and black horses turn buckskin, or that make red horses turn palomino and black horses turn another type of buckskin, etc., etc., etc.  I suppose at one time or another, many of these may have been mutations--but colors such as dun and buckskin had high selective pressur
e, as they were more camoflaged on grasslands, etc., and were/are quite common in wild equids.  Since melanoma is most often a disease that occurs in old age (or at least comes on slowly, so the horse is not adversely affected until old age), even with a genetic predisposition for it among grey horses, most who get it have had plenty of time for an ample reproductive career, hence it would not be something that would be selected against in nature.  Grey horses have certainly been around a long time in terms of horse history.

Heidi