t 
58 MendeF s Laws of Inheritance. 
been traced by Hurst from a careful analysis of the records 
given in Weatherby’s Ge?ieral Stud Book of Race Horses. 1 
In this great work the parentage, sex, and coat colour of all 
British thoroughbreds is given, and the records appear to have 
been kept with unusual care. From the data given there it 
is clear that chestnut colour is recessive to bay and brown, 
and consequently wherever one of these latter colours is 
mated with chestnut the offspring is bay or brown. By way 
of example, St. Simon, St. Serf, Galopin, Ladas, Merry 
Hampton, and Cabin Boy, all either bay or brown animals, 
have given 370 foals when mated with chestnut mares, and 
without exception these have proved to be bay or brown. In 
this group of sires each was pure with regard to the colour of 
the coat. As is only to be expected, though some sires were 
not so, a bay or brown resulting directly from a cross with 
a chestnut would not be pure, for instance, though one could 
not detect this without actually breeding from it. There is 
in this case no mark of the hybrid to correspond with the 
speckling of the face of the hybrid black and white faced 
sheep. Hurst has picked out a series of these cases and shown 
that twelve such sires, when mated with chestnut mares, have 
produced an approximately equal number of bay or brown 
and chestnut foals. The actual figures are 355 and 347. A 
typical case is afforded by Isinglass, one of whose parents was 
a chestnut. Mated with chestnuts he gave 62 foals, 28 of 
which were bay or brown and 34 chestnut. These figures are 
•a sufficiently near approach to equality where comparatively 
small numbers are concerned. 
Calling bay or brown D and chestnut R , the sires in these 
cases are DR , and they produce both D and R gametes in 
equal proportions. The chances of combination may be 
represented as follows : — 
Female gametes Male gametes 
giving DR or RR in equal proportions. As bay or brown is 
dominant over chestnut the DR " s will appear to be pure bay 
or brown. As chestnut is recessive to these colours when 
mated with chestnut, no matter what the descent, it must give 
chestnut. Hurst illustrates this point by an analysis of 100 
chestnut sires of various extraction mated with some 600 chest- 
nut mares again of varied descent. These gave a total of 1,104 
recorded foals, of which 1,095 are entered as chestnut. In 
1 Proc. Roy. Soc., Yol. 77, page 390. 
