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RE: [RC] [RC] ? favorite color - RDCARRIEIn a message dated 3/9/2005 12:17:20 PM Eastern Standard Time, "Melissa Alexander" <mcalex@xxxxxxxxxx> writes: Barbara, say there's one gene that controls coat color -- simple inheritance, I believe that's called. (In practice, I don't *think* horses have just one gene involved in color inheritance, but the definitions of homozygous and heterozygous hold up.) In simple inheritance, an individual horse inherits one part of that gene from his father and one part from his mother. If the horse inherited the same color gene from both parents, that horse would be homozygous for the color. If each parent contributed a different color gene, that horse would be heterozygous for whichever color was dominant. Each individual horse, then has two parts to this color gene. He can pass on only one to a particular offspring. Which one he passes is determined by a genetic roll of the dice.
Melissa is on the right track with heterozygous and homozygous, dominant,
recessive, etc. In Arabians, there are actually just two forms of the "color"
gene - red (chestnut) and black. Black is dominant over red. That's why you
can get a chestnut from two non-chestnut horses...it's because those two
non-chestnuts were each carrying one of the recessive (hidden) chestnut forms
of the color gene.
Then you have modifier genes that work on these two basic colors. The bay
modifier: the dominant form of this one works on black to restrict it to the
legs, mane, and tail (so a bay is a black horse with the dominant bay
modifier). The recessive form is neutral...ie, that's what a black horse has -
the black is *not* restricted. A chesnut horse can have the dominant form of
the bay modifier, but because it has no black coat pigment to be acted upon,
you can't tell it carries it. Then there's the gray modifier, that works to
turn the base coat color gray. The dominant form turns the horse gray, the
recessive form does not. Other horse breeds have a bunch of other color genes
such as dilute (which give palomino, buckskin, etc.), tobiano, overo, dun,
etc., but Arabs are mercifully much simpler. :) Sabino markings on
Arabs...don't ask me the genetics of that one, because I haven't a clue. <G>
I'm sure someone else could have explained this much better, but I'm a blonde,
so...
Dawn in East Texas
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