1022-7954/02/3807- $27.00 © 2002
Russian Journal of Genetics, Vol. 38, No. 7, 2002, pp. 725–734. Translated from Genetika, Vol. 38, No. 7, 2002, pp. 869–880.
Original Russian Text Copyright © 2002 by Chadov.
From a mode of inheritance of the characters, Men-
del had determined the major properties of the genetic
system. These are discreteness, diploidy of the heritable
factor (two alleles), and independent inheritance of the
factors. According to the Mendel’s scheme, as is known
today, the DNA sequences inherited by the descendants
from their parents ensure the development of the traits.
However, not only the general organization of the
genetic system accounts for the conformity of the trait
to gene inheritance. The two other particular conditions
should be met, which are (1) the complete or nearly
complete gene expression, and (2) the uniqueness of the
gene (one copy).
In the published genetic literature, many cases of
noncanonical trait inheritance have been described.
Some of them were satisfactory explained by incom-
plete penetrance and multicopy-number of the relevant
gene. There is now evidence suggesting that the varying
penetrance and multicopy-number genes are character-
istic of a large group, and, probably, of most of the
genes contributing to regulatory regions of the genome.
Recently, based on evolutionary reasons, it has been
proposed, that a special group of mutations exist, which
are viable in a homozygote, but nonviable in a het-
erozygote. By a special procedure, these mutations
were isolated from the progeny of
The mutations were localized to the X chromosome.
A male carrying such mutation is viable and fertile.
However, crosses with females of the
strain yielded no daughters. In the ﬁrst case, the muta-
tion is not a lethal, whereas in the second case, it is
expressed as a dominant lethal. For this reason, these
mutations were designated as facultative dominant
lethals . They were assigned to the group of regula-
tory gene mutations .
Similarly expressed mutations were detected in
autosome 2 of
[3, 4]. Later, many other
unusual properties of them were revealed . These
mutations are analyzed in this study as the representa-
tives of regulatory mutations and compared with the
“common” mutations, i.e., mutations at the structural
genes. In the current genetic literature, the “image” of a
mutation generally is related to a structural gene muta-
tion. However, the “image” of the regulatory-gene
mutation is essentially different. We discuss the charac-
teristic expression of the regulatory-gene mutations in
, which is assumed to depend on the speciﬁc
structure of the regulatory gene. The ﬁrst of these spe-
ciﬁc features is that only one of the pair of homologous
genes is in an active state. The second is that the regu-
latory gene contains a block of several alleles, each of
which can fulﬁll the same regulatory function. Thus, in
the regulatory part of the genome, or in a considerable
portion of it, (1) each gene is normally represented by a
cassette of alleles and (2) only one allele in one of the
parental chromosome sets is expressed.
OBTAINING A COLLECTION OF MUTATIONS
IN THE X CHROMOSOME
crossed to females carrying attached-X chromosomes.
Each of the patroclinous sons, who received an irradi-
“The Image” of the Regulatory Gene
in Experiments with
B. F. Chadov
Institute of Cytology and Genetics, Siberian Division, Russian Academy of Sciences, Novosibirsk, 630090 Russia;
Received July 5, 2001
—The mutants referred to as facultative dominant lethals were selected in the progeny of gamma-irra-
males. The mutant males were viable and fertile, though their crosses with females of the
line yielded no daughters. The mutations obtained differed from the common mutations by (1) extremely
varying penetrance of F
hybrids from crosses with various lines; (2) the uncertain relationships between the
mutant and normal alleles; (3) the different expression in somatic and germ cells; (4) the dependence of the
expression on the sex of the parent that was the donor of the mutation; (5) the mass morphosis formation and
(6) the frequent reversal to the norm. These mutations are assigned to the regulatory group and their speciﬁc
expression (see above) can be helpful in identifying regulatory gene mutations. We assume that the speciﬁc
expression of the mutations studied is related to speciﬁc properties of the regulatory genes. These properties are
as follows: (1) only one out of two homologous regulatory genes is in an active state, (2) in the haploid chro-
mosome set, the regulatory gene is represented by several alleles (
-alleles); (3) only one allele ensures the
regulatory gene activity.