1062-3604/05/3604- © 2005 Pleiades Publishing, Inc.
Russian Journal of Developmental Biology, Vol. 36, No. 4, 2005, pp. 225–229. Translated from Ontogenez, Vol. 36, No. 4, 2005, pp. 274–279.
Original Russian Text Copyright © 2005 by Inge-Vechtomov.
The concepts of heredity and variability are closely
related not only as subjects of genetics, but also as a
dual characteristic of living systems. At the same time,
further deepening of our ideas about the mechanisms of
inheritance requires a more detailed consideration of
both mechanisms and types of variability. The currently
accepted classiﬁcation of variability, hereditary (com-
binative and mutational), modiﬁcation, and ontogenetic
(Inge-Vechtomov, 1989; Fig. 1), has recently less and
less satisﬁed us. Let us remember epigenetic variability,
which is not represented in this classiﬁcation. This is a
next “incantation” which undoubtedly complicates the
classiﬁcation, but does not propose a new conceptual
view of the problem of variability as a whole.
Let us remind that there is no so far a satisfactory
deﬁnition of mutation. Mutations are usually deﬁned
not only as base substitutions or inserts-fallouts of base
pairs in DNA, but also as so-called genomic mutations,
i.e., changes in the number of chromosomes, including
polyploidization occurring due to defective work of the
mitotic spindle proteins (Lobashev, 1967). In addition,
polyploid series can be obtained by controlled hybrid-
ization, like in
yeast. Mutations are
also deﬁned as chromosome mutations (rearrange-
ments), which arise in overwhelming majority due to
exchanges between nonhomologous genome regions or
between partially homologous regions located in differ-
ent parts of the genome due to so-called ectopic or ille-
gitimate recombination (Leu
, 1998). In the same
way, the now habitual expression transposon or inser-
tion mutagenesis actually implies recombination events
that determine incorporation of a foreign DNA element
or transposon in the genetic material (Glazer, 1998).
Thus the concept of mutation unites the results of
events, which differ signiﬁcantly in their mechanisms.
Hereditary and, especially, mutation variability is
traditionally divided into spontaneous and induced,
implying that the reproduction of genetic material is
characterized by a certain level of “errors,” which can
increase under the inﬂuence of environmental factors—
mutagens. At the same time, modiﬁcations, ﬁrstly, are
usually related to the factors of habitats and, secondly,
are commonly considered as adaptive changes. Both
concepts are mostly wrong.
It is often forgotten that Astaurov published his clas-
sical work on variability of
already in 1927 (Astaurov, 1927), in
which he demonstrated that modiﬁcation variability
can also be spontaneous (see also Tikhodeev and Zhu-
rina, 2004). Astaurov described a mutation (unfortu-
nately, lost later), transformation of halters into the sec-
ond pair of wings (Fig. 2), with “incomplete pene-
trance” and “varying expressivity” (terms of
N.V. Timofeeff-Ressovsky proposed in the same
year—Timofeeff-Ressovsky, 1927). It turned out that
Role of Genetic Processes in Modification Variability.
Prophecy of B.L. Astaurov
S. G. Inge-Vechtomov
St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 119034 Russia
Received February 25, 2005
—In his pioneering work on mutation
, B.L. Astaurov discov-
ered spontaneous modiﬁcations based on variability in gene expression. This new approach to the phenomenon
of modiﬁcations should be considered as the ﬁrst stimulus to development of the general theory of variability.
Contemporary classiﬁcation of variability based predominantly on phenomenology encounters many contra-
dictions. The same speciﬁc molecular mechanisms may be responsible, for example, for both hereditary and
nonhereditary variability depending on the taxonomic status. Some mechanisms responsible for both mutations
and modiﬁcations or for mutations, recombination, and ontogenetic variability have been considered from this
viewpoint. It may well be more productive to consider different types of variability with respect to the main
genetic processes: replication and expression of genetic material.
: modiﬁcations, variability, gene expression.
MATERIALS FROM THE CONFERENCE DEDICATED
TO THE CENTENARY OF B.L. ASTAUROV
Combinative Mutational Ontogenetic
The present-day classiﬁcation of the types of vari-