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From: sbishop@desire.wright.edu
Newsgroups: sci.bio
Subject: Re: Confused about horse color...
Message-ID: <1991Feb7.131152.2463@desire.wright.edu>
Date: 7 Feb 91 18:11:52 GMT
References: <15746@milton.u.washington.edu> <6130@ncsugn.ncsu.edu>
Organization: University Computing Services, Wright State University
Lines: 31

In article <6130@ncsugn.ncsu.edu>, annw@ncsugn.ncsu.edu (Ann Williams) writes:
> Kathleen,
> 
>    The books that I go by use the letters bb and not cc as chestnut.
> The B meant black pointed horses and bb is non black pointed horses 
> which are the chesnuts. Also I use the Cr as the dilution gene. 
> So Bb or BB with the Cr would make buckshin and bb with the Cr is
> palomino. The dominant A (red) is also needed to have the diution 
> gene expressed in the body coat or phenotype. I was grouping the bays
> and buckshins together becaue of the B gene common to both and the 
> palominos and chestnuts together because of the lack of black points.
> On the subject of the Bay stallion and Grey mare producing a chestnut.
> For this to happen both parents had to be heterozygous. That is both 
> carried the recessive bb or as you say cc chestnut. Now correct me if
> I am wrong but two heterozygous horses have a 25% chance of producing
> the recessive color not 12.5%. Or am I missing something? 

I think what you are missing is the fact that the Grey allele is on a 
different locus.  So even though the one parent is heterozygous Grey,
the Grey gene can over ride the bb color if combined.  The genotype of 
the grey parent can be Grey/chestnut, nogrey/chestnut, grey/bay, nogrey/bay.
This is tenative since it is not certain that the grey parent carries
bay also.  This is possible since the mare has produced bay offspring.  
Only if it produces a bay offspring out of a chestnut stallion would it
be proof that there is bay present.  Otherwise, it COULD be just carrying
chestnut.  And it is possible that there is only one chestnut gene and
nothing at all on the other part of the pair.  So still another possibility 
is grey/nochestnut, nogrey/nochestnut.  

I hope I figured that all out right.....  If anyone sees a flaw in this
please let me know...