1022-7954/05/4103- © 2005 Pleiades Publishing, Inc.
Russian Journal of Genetics, Vol. 41, No. 3, 2005, pp. 333–336. Translated from Genetika, Vol. 41, No. 3, 2005, pp. 422–426.
Original Russian Text Copyright © 2005 by Beketov, Kashtanov.
Sex ratio at birth is usually close to 1 : 1 (i.e., about
50% of males and 50% of females) in most mammals
. However, offspring of predominantly one sex is
often required in farming practice. For example, prefer-
ential breeding of males is a speciﬁcity of fur farming.
The main reason is that males of all species bred in
cages at fur farms have longer hair and larger body than
females. This is essential because hair quality and skin
size are the most important commercial characteristics
in fur farming, largely determining the price of fur.
Therefore, the factors affecting sex ratio in fur ani-
mals are intensely studied. Studies on the dependence
of the sex ratio at birth on breed-related  and age-
related  differences of parents are noteworthy. There
is evidence that the proportion of males in the offspring
is also affected by litter size  and fertility . These
studies have been performed on blue foxes , red
foxes , minks [2, 4], and sables .
The role of genetic factors in the control of sex ratio
at birth in mammals is even more important from both
scientiﬁc and practical viewpoints. The variation of sex
ratio in families, which has not been studied thus far in
any fur animal, is of special interest.
Therefore, we analyzed the sex ratio at birth in a
commercial population of the blue fox using biometric
methods and performed family analysis to detect parent
lineages and families where offspring of one sex was
We used the data from the 1985–1989
records of the Pushkinskoe Breeding
Fur Farm (Moscow oblast) on blue foxes (the Vual-
evaya breed). A total of 1380 births of 906 females (a
total of 15 396 cubs) were analyzed. Litters containing
stillborn offspring or offspring of unidentiﬁed sex were
excluded from the analysis.
Statistical treatment of the data was formed accord-
ing to Khromov-Borisov . The total proportion of
males among the blue foxes that were born from 1985
to 1989 was 55.1% (
< 0.01). The proportion of male
offspring varied in different years from 0.537 (53.7%)
to 0.562 (56.2%) in 1986 and 1989, respectively. It is
clearly seen in Fig. 1 that all the ﬁve points showing the
sex ratios in different years are located above the theo-
retical straight line corresponding to the expected 1 : 1
ratio. In other words, more males than females were
born every year in the period studied, with the deviation
from the expected ratio (1 : 1) being statistically signif-
The predominance of one sex in newborn offspring
may be a hereditary character determined by genetic
mechanisms. Taking into account this presumption, as
well as the fact that each parent mates with several part-
ners during the entire reproductive period, we analyzed
pooled data on the families formed by individual males
and females. The families in which less than three mat-
ings were observed were excluded from the analysis.
Finally, we analyzed the data on 287 families formed
by speciﬁc males and 106 families formed by speciﬁc
We used Khromov-Borisov’s statistical table  to
analyze the segregation with respect to sex in families.
Taking into account that not only families with predom-
inantly male newborn offspring, but also those with
predominantly female offspring, were found in the blue
fox subpopulations studied, we used a two-way test for
estimating the signiﬁcance of the difference
Effect of the Hereditary Characteristics
of Male Blue Foxes
L. on the Sex Ratio
of Their Offspring
S. V. Beketov and S. N. Kashtanov
Vavilov Institute of General Genetics, Russian Academy of Sciences, Moscow, 119991 Russia;
fax: (095) 135-12-89; e-mail: firstname.lastname@example.org
Received August 18, 2004
—Family analysis of a commercial population of the blue fox (the Pushkinskoe Breeding Fur Farm,
Moscow oblast) with respect to secondary sex ratio has been performed. The offspring of each individual male
or female involved in crossing between 1984 and 1988 was analyzed. The study of all families formed by every
male and every female has made it possible to determine a group of “outstanding” fathers (23 out of 287 males),
whose offspring was predominantly male (62.1% of the offspring were males, versus 53.9% in the total popu-
lation). The results of subsequent detailed study on the pedigrees of male blue foxes in whose offspring the sex
ratio signiﬁcantly deviates from 1 : 1 indicate that this character is transmitted from fathers to sons without the
deterioration of other commercially valuable characters. It is presumed that the signiﬁcant deviation of sex ratio
from 1 : 1 in the offspring of some male blue foxes is determined by genetic factors.