264
ABSTRACTS
60 are reported and amnion preparations in cases of
54. A study of the chromosome complex of germ cells,
therefore, was undertaken in the hope of establishing the
exact number of chromosomes present in sheep. Modern
techniques were employed.
Chromosome counts were made on more than 65
spermatogonial cells, taken from lambs which had
just attained sexual maturity. Many of the chromo-
somes in these cells showed very little over-lying or
touching so that they were easily distinguished one
from the other. The diploid counts were consistently
54. 'Metaphase plates of the primary spermatocytes con-
tained 27 chromosomes.
Morphologically the chromo-
somes of the sheep consist of a sphere; rods which may
be long, short or bent; and large V's. These latter vary
somewhat in size and symmetry, but were distinctly
observed to be V-shaped single chromosomes and not two
rods so arranged as to give the appearance of a V by the
over-lying of one end of each. Since there were three
pairs of these present involving six individual chromo-
somes, the authors suspect that other workers may have
considered them each made up of two rods over-lying at
one end thus explaining counts of 60. The remaining
48 chromosomes consist of two pairs of slightly bent,
medium sized rods, 43 straight rods varying from 4 to
1.5 microns long, and one sphere. Observations on the
anaphase showed this one sphere paired with a medium
sized rod.
Considerable difference of opinion exists in reference
to which chromosomes constitute the sex or X-Y chromo-
somes. The authors of the present study believe the
heteromorphic pair, viz. the medium sized rod and the
small sphere, are the X-Y chromosomes. They do not
think that the fact that different workers have studied
three breed groups, two wild species, and hybrids of
these wild species with domestic sheep' explains the
variations reported in chromosome number or the diffe-
rence in opinion on the morphological type of the X-Y
pair. [J.N.W.]
The inheritance of paralysed hind legs, scrotal
hernia and atresia ani in pigs. S. BERGE (1941)
J. Heredity 32, 271
WRIEDT reported the appearance of a recessive sub-
lethal factor in a herd of Norweigian Landrace swine.
Piglings born to heterozygous matings were 25 per cent
effected.
Symptoms were paralysed hind legs, the
animal being unable to walk, although it could pull
itself along with the forelegs. Koroveckaja reported a
similar anomaly in Russia, but the proportion of
affected piglings was 19.5 per cent, which is less than
would be expected of a monogenic recessive factor. It
is also reported that in certain other cases the forelegs
were involved in individuals of the Large White breed
in Sweden and the German Landrace. The forelegs
were either bent or greatly enlarged.
Warwick suggested that scrotal hernia in pigs was
due to a digenic recessive, and Koroveckaja reported
57.1 per cent males in those litters in which the character
was found. The author believes that the factor shows
incomplete dominance and points out that, whereas the
proportion of males in 414 litters at the Pig Breeding
Station, Aas, Norway was 46.9 per cent, the proportion
of males in those 31 litters in which scrotal hernia was
manifest was 57.14 per cent.
'The excess of males is
obviously caused by the fact that litters with a large
number of males have a greater probability to reveal one
or more cases of hernia' he says, and confirms a domi-
nant umbilical hernia in the pig reported by Wriedt.
Cases of atresia ani are referred to. Both sexes are
involved; the males usually dying after about two or
three days of age due to obstruction, the females
generally having an opening from the ventral side of the
rectum to the sheath which prevents obstruction. Some
sows live to maturity and breed. The mode of inheri-
tance of the character is irregular. It was found to be
dominant in many cases. Two boars, Jarl and Frikk,
had 21.2 and 13.3 per cent affected pigs in their
litters respectively. Males and females were equally
affected. Two sisters bred to Frikk, their father, gave
16 per cent affected offspring, but bred to Jarl they
gave 26 7 per cent. The author contents that this shows
that a monogenic mode of inheritance is out of the
question, but he is unable to list the factors involved.
Practically, it is impossible to purchase pigs for breed-
ing purposes that one might be certain are free of the
genes, causing this character. [J.N.W.]
Genetics of the fowl. 15. Multiple spurs, a muta-
tion linked with duplex comb, F. B. HUTT
(1941). J. Heredity 32, 357
THE modern Black Sumatra cock must have atleast
three spurs, according to the American Poultry Club.
This breed of chickens dates back in the United States
to importations in 1847. Females have no spurs.
In
appearance this breed looks much like game fowls, of
which certain ones, said to have originated in India,
may have as many as five spurs.
At hatching time there is no difference between the
male and female. In adult life the female shows
only several enlarged scales at the spur site. Young
males show gradual development of several spurs each
of which develops much as one would on a single-
spurred breed.
In the adult male the top spur is
generally smaller than the second or largest.
Those
below are smaller in a descending order. Those which
are larger have a separate bony core. Although sexing
on the basis of scale appearance at the spur site in the
new born chick is not possible, 93 to 98 per cent accu-
racy is obtained at this age when selecting those that
will have multiple spurs from those which will have
only a single spur.
During a six year period, involving F 1 F 2 and back
cross population of a Black Sumatra male and Single
Comb White Leghorn females, all the F 1 75 per cent.
of the F 2 and 50 per cent. of the backcrosses showed
multiple spurs. This indicated a unifactorial dominant
character. The symbol M was assigned to the gene.
Evidence, however, from the progeny of one Single Comb
Ancona cock, mated to four Mm hens, to test for the
linkage of M, showed that there was, sometimes, a
factor that suppressed M, in this case in about 46 per
cent of his Mm progeny.
Tests for linkage showed that M does not belong to
either of the four autosomal linkage groups previously
known, but that it is linked with D, which causes
duplex comb. The finding of this relationship estab-
lished a fifth linkage group. There was some suppres-
sion of D noted in this study, but there was no indi-
cation that the suppression of D was associated with
the suppression of M. [J.N.W.]
Hydrocephalus, a lethal in cattle. C. L. COLE and
L. A. MOORE (1942). J. Agri. Res. 65, 483.
BOTH internal and external types of hydrocephalus
have been reported in most animals including man.
The condition has sometimes been thought to be lethal
in swine and mice; various
degrees of association
between hereditary and/or lethal hydrocephalus and