1022-7954/05/4102- © 2005 Pleiades Publishing, Inc.
Russian Journal of Genetics, Vol. 41, No. 2, 2005, pp. 174–181. Translated from Genetika, Vol. 41, No. 2, 2005, pp. 237–245.
Original Russian Text Copyright © 2005 by Nikitin, Knyazev, Orlova, Bekenev, Danil’chenko.
Many models have been already developed to
describe a genotype dependence on the phenotype of a
quantitative trait [1–9]. These models are traditionally
based on the mean trait values in different genotypic
classes though they also describe the relationships
between trait variation (variance) and genotype.
Rozhkov and Pronyaev  proposed a model pos-
tulating a nonspeciﬁc relationship of quantitative traits
and homo- and heterozygosity for the enzyme genes
that control the rates of biochemical reactions (i.e., the
metabolic pathway genes). However, this model was
developed to explain the phenomenon of “systemic het-
erosis”  and thus has signiﬁcant limitations. First, it
deals with genetically homogeneous samples, where
quantitative trait variance independent of the genes that
control the biochemical reaction rate is equal to zero.
Therefore, it cannot be used in the case of samples
where the quantitative trait variance independent of the
tested gene signiﬁcantly differs from zero, i.e., for
genotypically heterogeneous populations, which
includes practically for all populations of animals [11–
13]. Second, this model postulates that in homozygotes,
variance of a quantitative trait permanently exceeds this
parameter in heterozygotes, which is not always true
for real populations. Thus, this model is conﬂicting
with some classic views, for instance, with gene bal-
ance hypothesis [11–13].
Each organism is believed to be as an integral sys-
tem  whose growth and development is controlled
by all of its genes. The individual phenotype depends
signiﬁcantly on the “genetic background,” the complex
of genes affecting the speciﬁc expression of the geno-
type for a certain gene . The contribution of the lat-
ter to the value of a quantitative trait in an individual
depends on the genetic background of this individual.
The same genotype may enhance or reduce the expres-
sion of a trait depending on the genetic background.
Thus, the genetic background of a genotype is repre-
sented by the genetic background of the population,
where this gene exists . Hence, interaction of differ-
ent alleles of some gene with the same factor must have
different effects on the individual growth and develop-
ment. Conversely, the growth and development of indi-
viduals with the same genotype may vary signiﬁcantly
depending of the genotypic background and environ-
mental conditions. Thus, in a population polymorphic
for many genes, the growth rate variation in individuals
with the genotypes identical for a particular gene is a
consequence of diverse interactions between the geno-
type alleles and the remaining population genetic back-
In this study, we aimed to formalize and test a model
that describes a relationship between variation of a
selectively important quantitative trait in animals and
their homo- and heterozygosity at the genes controlling
the biochemical reaction rates. This model includes all
cases of gene control of a quantitative trait and is suit-
able for real populations.
MATERIALS AND METHODS
Two populations of the Large White breed of pigs
(NKB-1 and NKB-2) from the Bol’shevik stock farm,
Novosibirsk oblast , were used to test the model.
The average daily increase in animal live weight during
control fattening was chosen as a complex selectively
important quantitative trait measuring growth rate of
the animals. This trait shows wide variation, depends
on numerous genes, and is under selection.
A Model for the Effect of Homo- or Heterozygosity
on Animal Growth Intensity
S. V. Nikitin
, S. P. Knyazev
, G. V. Orlova
, V. A. Bekenev
, and N. V. Danil’chenko
Institute of Cytology and Genetics, Siberian Division, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Novosibirsk State Agrarian University, Department of Animal Breeding and Genetics, Novosibirsk, 630039 Russia
Siberian Scientiﬁc and Technological Research Institute of Animal Husbandry, Russian Academy of Agricultural Sciences,
Krasnoobsk, 633128 Russia
Received August 4, 2003
—A model has been developed that describes the dependence of a quantitative selective trait on the
animal homo- and heterozygosity for the genes that control the biochemical reaction rate (isoenzyme systems).
The model includes any cases of gene control of a quantitative trait and is applicable to real, genetically heter-
ogeneous populations. The results of testing the model show that it can be used for identifying the genes
involved in additive polygenic determination of quantitative commercially valuable traits.