S20 
IOWA ACADEMY OF SCIENCE 
THE GRAYS. 
Gray is recognized as a separate factor by all writers. There seems 
some question as to whether it can operate in the absence of H, black 
pigment, but Sturtevant presents evidence to show that it does. It is 
dominant to all factors previously named, dappling D and restriction B 
excepted, and varies from a deep iron gray in young stock to the white 
or flea-bitten gray of the older animal. 
It is a simple factor since animals heterozygous for it produce 50% 
grays and 50% other colors. Dr. L. J. Cole of the University of Wis- 
consin has told the writer in private communication that one of his 
students has totaled the offspring of grays in the Clydesdale studbook 
and has obtained exactly 50% of each of grays and other colors. The 
Clydesdale breeders have objected to gray and have always bred their 
gray mares to other stock in order to reduce the chances of its appearance. 
Gray stallions since 1831 have nearly all been castrated. This has 
resulted in all the grays being heterozygous. 
Sturtevant shows 400 gray to 428 not gray for the same condition, 
while he exhibits 45 gray to 15 not gray where both parents are 
heterozygous. 
Gray is characterized by an intermingling of pigmented with non- 
pigmented hairs, usually associated with dappling. It seems possible that 
gray may be a combination of dappling and the roan factor although 
the above evidence indicates that it is a unit in action. 
THE ROAN PATTERN. 
Roan seems dominant to all the other colors and is apparently a pat- 
tern entirely independent of the kind of pigment. Two kinds of roans 
exist visually, strawberry or red roan, and blue roan. These probably 
correspond to bays and blacks plus the roan pattern. It seems probable 
that there also exists a chestnut roan, in fact they are apparently quite 
common for roans with red pigmented manes and tails instead of black 
are seen frequently. Such a roan would probably be the type produced 
by the mating of blue roan to blue roan shown in the table. If the 
black factor were heterozygous in both sexes, the chestnut roan would 
result. 
Roan differs from gray in lacking the dappling common to gray and 
in possessing quantitatively a much larger number of pigmented hairs. 
It has seemed to the writer that gray may be a combination of the roan, 
dappling and dilution factors coupled together in some way, but since 
from the present evidence that would necessitate considering gray epis- 
