ABSTRACTS
263
The inheritance of equine coat color. The basic
colors and patterns. G. W. SALISBURY (1941).
J. Heredity 32, 235
THREE sources were used in obtaining information
about the Inheritance of the more common colours, some
specific colours and face and leg markings of the horse.
These sources were the American Shetland Stud Book,
the Studbook for Finish Horses and the records of the
Jockey Club. Varying amounts of data on body colour,
colour of mane and tail, white markings and other pat-
terns are presented.
Basic or foundation colours are listed as bay; brown;
brown-black or seal brown; black; and liver chestnut;
chestnut and sorrel. Colour may vary with age and ex-
posure to sunlight, making it difficult to properly classify
horses on the basis of colour.
Undoubtedly (1) brown-black ponies were classified
frequently as black instead of brown and (2) colts were
improperly classified before the shedding of the foal
hair whose colour may differ from the basic body colour.
Despite these possible errors, brown is an important
colour in the Shetland breed. Furthermore, different
shades of chestnut were not distinguished by Shetland
breeders. However, a study of 3,235 Shetland matings
indicated that the mode of inheritance of the basic body
colours is the same in this as in the larger breeds of
horses.
Wentworth reported that the light mane and tail of
the Belgian horse were due to a monofactorial recessive
to the normally pigmented mane and tail. The present
study suggests, however, that it is more complicated,
involving at least two recessive pairs of homozygous
genes, with additional genes which modify the shade of
the coat and also tend to influence the amount of
pigment in the mane and tail. The white mane and
tail seem to have the same inheritance in the chestnut
as in the sorrel.
Genes which are epistatic to the basic colours are
'those responsible for the grey colour, roaning, spotting,
dominant white colour, and dilution of the basic colours.
Observations on 106 matings indicate that grey is pro-
duced by a dominant gene which is epistatic to the
basic colours. The roaning gene acts similarly. There
are two types of white spotting, each with a different
inheritance. Extensive spotting is due to a dominant
white spotting gene whereas limited spotting seems to
be due to more than one pair of genes which may involve
both dominance and recessiveness. Slight breed diffe-
rences were noted which may be due to the 'unconscious
selection practised in the development of these breeds.'
A single dominant gene, epistatic to all colours, is
indicated in certain white horses although this condi-
tion is confused with both old homozygous gray and
the results of the dilution gene on chestnut or sorrel.
The dilution gene is not discussed in this paper.
[J.N.W.].
The inheritance of equine coat color. II. The
dilutes, with special reference to the Palomino.
G. W. SALISBURY and J. W. BRITTON (1941)
J. Heredity 32, 255
THE Palomino is characterized by a cream-coloured
body, varying from a dark gold to a light, washed out
yellow, with a white mane and tail. The eyes show a
bluish-pink appearance, the skin is pink.
Certain previous workers called this colour cream, as
distinguished from dun which referred to horses with a
light body colour, black mane and tail, a dorsal stripe
and often with 'Zebra-striped' legs. Those duns of a
more yellow colour are commonly called buckskin.
Wredit is reported to have felt that cream was an
unflixable heterozygous condition, this theory is substan-
tiated by breeding experiments. Heizer 'considered that
dun, mouse, and cream are produced by a dominant
dilution gene superimposed over certain basic body
colors'. Tuff accepted this postulate but cconsidered
that a pair of genes, responsible for the quantity of
pigmentation, was involved. In the homozygous resces-
sive condition this pair produced albino; he called it the
albino factor. In the heterozygous condition the pair
reduced chestnut to cream, bay or brown to buckskin,
and dun to light dun, but had no influence on black of
mouse'. His dilution gene, therefore, was dominant.
Gremmel, on the other hand, concluded that the albino
was a homozygous recessive for genes at three major
loci of which one dominant at the first locus produced a
Palomiono, while two dominant genes at this locus gave
a red ysabella or sorrel. He denied any relationship of
the Palomino to dun.
The authors of the present study were confronted,
therefore, with two postulates : one explaining Palomino
by the basic chestnut or sorrel plus a dominant dilution
gene, which also dilutes bay or brown to dun, and black
to mouse; the other being chestnut or sorrel possessing
a recessive member of a pair of genes responsible for
basic pigment.
A study of the American Shetland Stud Book and
visits to Palomino breeding establishments provided
material for the present work. The Shetland pony data
indicated a dominant gene was responsible for cream,
dun and mouse colours. Matings involving two animals
with the dominant dilution gene gave mostly dilutes,
where one parent was a dilute and one solid-coloured,
the ratio of dilutes to non-dilutes was very close to the
expected 1:1. No differences were found between
creams and Palomino so far as colour, type or distribu-
tion of colour was concerned. A relationship between
these two colours, therefore, seems obvious. Visits to
some Palomino breeding establishments as well as reports
from others unvisited indicate that 40 to 50 per cent
of the progeny of a Palomino stallion and chestnut or
sorrel mares were Palominos, the rest were chestnut or
sorrel. Breeding work of troop D, New York State
Police at Oneida, New York, gave similar results.
It is concluded, therefore, that the Palomino is pro-
duced by the presence of a diluting gene which does
not mask the effects of genes which cause intensity
variations. A basic chestnut with a white mane and
tail plus the dilution gene gives the most desirable
coloured Palomina. When the gene for black is absent.
the homozygous intensity reduction condition gives an
individual with practically no pigment in the hair.
When these are crossed on other colours the progeny
all show a reduction of the hair pigment. It is not
felt that where the gene for black is present, the
homozygous dominant dilution condition produces an
albino; the writers believe that such a case results in
a washed-out, light dun. It appears that only one
pigment reducing gene was involved in the horses
studied.
[J.N.W.]
The chromosome complex of domestic sheep
(Ovis aries) R. O. BERRY, (1941). J.
Heredity 32, 261
SEVERAL workers have reported on the number of
chromosomes in the domestic and wild sheep. Their
observations were made largely on testicular material
prepared by standard methods, or on the amnion. Most
of them reported a diploid number of 54 or 60. With
one exception, testicular material was used in cases where