From: tracy@scoraz.resp-sci.arizona.edu (Tracy Scheinkman)
Newsgroups: rec.equestrian
Subject: re: color question for Tracy
Date: 16 Nov 92 23:42:07 GMT
Organization: University of Arizona, Tucson, AZ

>Can a black mare/stallion both reg. as dk. bay/brown but really black
>except for eyes/muzzle/flanks with bay hairs produce a true black offspring?
>The filly I have is a result of the above cross.  She is very black with
>very little or no noticable bay on her.

	The answer is yes!  There are two ways that this can happen
depending on the parents' genetics.  1-- the parents are genetically
black aa horses but carry at least one P pangare gene and one p non-pangare 
(pronounced pan-gar-ray refers to the lighter areas on flank and muzzle)
thus their genotype is aaPp and when crossed would have a 25% chance
of producing aapp which is  true black.  2-- the parents are very dark
mahogany bays but both carry a black gene thus their genotype is
Aa and again they have a 25% chance of producing aa true black.  (This
is a very truncated description of how to get true black there are a
number of other genes which can cover up the presence of the black gene
which I haven't talked about because color possibilities like chestnut
were not mentioned.)  This aa form of black is also known as fading
black as it will bleach in the sun often causing horses with this color
that live outside a lot to have a red tinting at the ends of their
manes and tails, and reddens the facial hair and flank hair a lot, some
sun-faded blacks can almost look seal brown when their coats are really
fried.  However if kept indoors or covered a true black will be black.
This color differs from jet black E-d in that jet black does not fade at
all in the sun.

	By the way, a few postings ago there was a reference to Ben Green's
book called The Color of Horses in which he says that there is only one
pigment instead of two.  Keep in mind that his work was done in the
late 40's early 50's with a standard microscope and limited chemistry
knowledge.  His conclusion is incorrect.  There are two color pigments
available to horses, eumelanin which is responsible for black horses
and the black of manes and tails on bay horses and the uniform chocolate
brown color seen infrequently, and the mousy grey color of grullos; and 
phaeomelanin which is responsible for the chestnut color, the red body color 
of bays and the yellow body color of palominos and buckskins.  His book has 
some wonderful paintings in it, the section on greying is excellent, and the 
information about how the pigment granules line up in the hair follicles is 
excellent.  His only other errors are in reference to the rose grey color seen 
in Arabians which is a greying gene not related to roaning and in stating
that grey horses can come from the mating of two non-greys which is absolutely
impossible.  There is a roaning that peridically shows up in Arabians however 
it is not uniform over the body as he indicated but mostly concentrated around 
the barrel of the horse.  
	The best work on color genetics in horses is Horse Color by
D. Phillip Sponenberg and Bonnie V. Beaver, both are veterinarians.  He
continues to do research into horse color genetics and periodically
publishes new info.  There are hundreds of pictures in this book as well
as a very good chart which shows color gene interaction.

				Tracy and everybody