1022-7954/05/4110- © 2005 Pleiades Publishing, Inc.
Russian Journal of Genetics, Vol. 41, No. 10, 2005, pp. 1123–1129. Translated from Genetika, Vol. 41, No. 10, 2005, pp. 1369–1376.
Original Russian Text Copyright © 2005 by Bogdanov, Rozanov.
pygmy wood mouse) is genetically heterogeneous. In
particular, the heterochromatic part of its genome dis-
plays wide variability, while the number of chromo-
somes and their morphology are stable (2
= 48, all
chromosomes have a single arm).
Analysis of heterochromatin variation in
is complicated by irregularity of its manifestation,
which is observed even in different metaphase plates of
one individual with the use of standard methods of pre-
paring suspensions and slides  and C-banding .
Apparently, its low repeatability is explained by some
speciﬁc chemical and structural features of heterochro-
matic segments and (or) their different functional state
in different bone marrow cells. This complication can
be overcome by selecting on each slide several
metaphase plates with best manifestation and the max-
imum number of C-blocks .
The views on the character of
tiation in the heterochromatin amount in animal
genomes are controversial. The disputable issues con-
cern subdivision of the C-band variability range in this
species, namely, how many forms should be distin-
guished and what traits should be taken into account or
ignored because of their high population variability [3–7].
The taxonomic signiﬁcance of differences in this char-
acter has also been under debate: Orlov
[4, 5] have
suggested that the chromosomal forms of pygmy wood
mouse be regarded as independent species, but this
view was not supported by other researchers [3, 6–9].
One of the authors of the present work has earlier
described three chromosomal forms of
the basis of analysis of his own and literature data on
variation in size and the number of centromeric
C-blocks in the pygmy wood mouse karyotypes .
Owing to a wide range and relatively low precision of
the C-banding technique, the insigniﬁcant ﬂuctuations
of the character, which “disappeared” against the gen-
eral variation background when increasing the sample
size or adding material from related populations, was
not though to have a diagnostic value. The identiﬁed
Variability in Size of the Nuclear Genome in Pygmy Wood Mouse
A. S. Bogdanov
and Yu. M. Rozanov
Kol’tsov Institute of Developmental Biology, Russian Academy of Sciences, Moscow, 119334 Russia;
fax: (095) 135-75-83; e-mail: email@example.com
Institute of Cytology, Russian Academy of Sciences, St. Petersburg, 194064 Russia;
fax: (812) 247-03-41; e-mail: firstname.lastname@example.org
Received February 2, 2005
—Earlier, in an integral genetic study, the Asian and European races were distinguished within the
(pygmy wood mouse) and the European race was divided into the East European
and South European forms. Each of these groups differed from the others, in particular, in the quantity of the
centromeric heterochromatin in karyotypes of the animals. To establish the pattern of its changes in
in the present study the DNA content in splenocyte nuclei in all races and forms of pygmy wood mice was
assessed using DNA ﬂow cytometry. The heterochromatin amount in karyotypes and genome size were shown
to be correlated. The East European chromosomal race of
(Central Chernozem and Non-Cher-
nozem regions of Russia, Crimea Peninsula, Middle Volga region, and Southern Ural) and the Asian race of this
species (East Kazakhstan, Uzbekistan, and East Turkmenistan), which have respectively the highest and the
lowest amounts of centromeric heterochromatin in the karyotype, exhibit the greatest difference in the DNA
content in the genome. On average, the difference is approximately 8% in males and 6.7% in females; in both
cases, the ranges of variability were distinctly different. Against the general background of the trait variation,
the Asian race, whose members have the smallest DNA amount in their cells, looks homogeneous. The genome
of the South European chromosomal form of
(Caucasus, Transcaucasia, Carpathians, and Balkan
Peninsula), which exhibits an intermediate content of the centromeric heterochromatin in the karyotype, is
smaller that the genome of the East European race (by 3.2% in the group of males and by 1.9%, in the group of
females), but larger than that of the Asian race (by 5% in either sex). Thus, the variability of size of centromeric
C-blocks in pygmy wood mouse is likely to be associated with elimination (or, conversely, an increase in the
amount) of the genetically inert chromatin. It is suggested that a signiﬁcant contribution to the variability of
genome size in
is made by heterochromosomes, or, more precisely, their variable regions, which
seem to be largely heterochromatic.