SEX IN LIVESTOCK BREEDING 
Inheritance of Many Characters is Affected by Sex, but this Phase of Heredity 
Does Not Offer Great Possibilities to the Practical Breeder 
at the Present Time 
E. N. WENTWORTH 
Professor of Animal Breeding, Kansas State Agricultural College, Manhattan, Kans. 
OMATICALLY there are four 
types of inheritance with refer- 
ence to sex. The first category 
of character is entirely inde- 
pendent of sex; the second is linked to 
the sex-determining factor in trans- 
mission; the third differs in expression 
according to sex, although the zygotic 
constitution is the same; and _ the 
fourth is confined to one sex, although 
it may appear in a rudimentary form 
in the other. The first two groups 
develop independently of the secretions 
of the sex glands, the second two are 
conditioned in their development by the 
presence and activity of the testes or 
ovaries. In the first group fall the 
great bulk of characters observed in 
domestic animals; in the second a 
number of characters observed in insects, 
birds and man; in the third a few cases 
in mammals with an instance or two 
in insects; and in the fourth, the mass 
of secondary sexual differences found 
in birds and mammals. Just where the 
secondary sex characters of insects 
should be included is at present doubt- 
ful.! 
CHARACTERS INDEPENDENT OF SEX 
Evidence on characters totally un- 
related to sex is unquestioned, the 
hundreds of experiments substantiating 
Mendel’s law being cases in point. 
Some of these discoveries have been of 
real economic interest, as for example 
the transmission of the polled character 
in cattle or the inheritance of coat-color 
in horses. 
SEX-LINKED INHERITANCE 
The second group of characters has 
been of particular interest to investiga- 
tors, because of the parallelism afforded 
between the transmission of such char- 
acters and the distribution of the so- 
called X-chromosome in gametogenesis 
and fertilization. The practical ap- 
plication of this knowledge, however, 
seems at present limited to the field of 
poultry, although there are certain facts 
which point to an ultimate usefulness in 
the breeding of dairy cattle. 
THE BARRED PLYMOUTH ROCK 
The knowledge (Spillman, Goodale, 
Pearl and Surface) that the cock has 
apparently two doses of the sex-linked 
characters, while the hen has but one, 
has proved of value in the breeding of 
Barred Plymouth Rocks to the show 
standard. A certain shade of barring 
is desired in this breed and it has always 
been a difficult problem to get flocks that 
would produce both males and females 
that were standard. When standard 
males were mated to standard females, 
the progeny were too light and the 
females were too dark. Cocks that 
sired standard females always sired 
light males, while cocks that sired 
standard males always had to be mated 
to dark females for this purpose and 
moreover produced very dark daughters. 
The apparent explanation of this 
difficulty is that the factors which 
reduce the degree of pigmentation and 
produce the white bars are cumulative 
in effect, and the male that is duplex for 
the barring factor is lighter than a 
simplex male or the female. One 
needs, then, two flocks in order to 
produce standard fowls. The female 
producing flock will have light males 
while the male producing flock will 
1If the sexual glands of caterpillars are removed at a very early age, the butterflies produced by 
these caterpillars nevertheless show all the expected secondary sexual characteristics. 
It appears, 
then, that these characteristics are wholly independent of the secretions of the reproductive 
organs. 
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