Sex-chromosome heterochromatin variation in the wood mouse, <i>Apodemus sylvaticus</i>

Abstract

Variation in heterochromatin content, as revealed by G- and C-banding, was studied in the sex chromosomes of the wood mouse, Apodemus sylvaticus. The sex-chromosome heterochromatin was also characterized by DAPI staining. Variation in sex chromatin was recorded in extremely large (giant) sex chromosomes in certain individuals and populations. In some individuals, the Y chromosome was the largest element of the complement. Different variants of both the X and Y chromosomes were found within a single population. The variation is therefore a type of population polymorphism and should not be used for taxonomic discrimination.

The mammalian model for population studies of B chromosomes: the wood mouse <i>(Apodemus)</i>

“…This possibility can find support in extensive heterochromatin variation in the sex chromosomes that was reported in certain Apodemus species (Nová et al, 2002). An alternative view suggests that Bs could originate from autosomes of the standard set through polysomy with subsequent rapid inactivation (Vujošević and Ž ivković, 1987).…”

A chromosomal study on Greek populations of the genusApodemus (Rodentia, Murinae) reveals new data on B chromosome distribution

“…Almost identical karyotypes of A. flavicollis and A. sylvaticus, based on chromosome morphology and G-banding pattern, have already been previously reported (Soldatoviae et al 1975, Vujoševiae et al 1984, Giagia et al 1985, Nova et al 2002, Stanyon et al 2004. Concerning the notable differences on heterochromatin distribution in the karyotype of these two species, the results of this study agree with and reinforce those of other works that support the appearance of heterochromatin blocks in both telomeric and interstitial positions of numerous autosomal pairs of A. sylvaticus (Gamperl et al 1982).…”

“…The karyotypes of the sibling species A. flavicollis and A. sylvaticus are considered to be pretty conservative with 2n = 48, FN = 48, all acrocentric chromosomes (Vujoševiae et al 1984), despite the occasional report of variations, eg giant X chromosomes (Nova et al 2002) or very large Y chromosomes (Zima 1984) in populations of A. sylvaticus from the Czech Republic. On the other hand, the karyotype of A. epimelas is distinguished from those of the two previous species, because it contains one or two pairs of small metacentric autosomes (2n = 48, FN = 50-52), attributed to pericentric inversions (Soldatoviae et al 1975, Vujoševiae et al 1984, Giagia et al 1985, Belcheva et al 1988.…”

Cytogenetic and Molecular Evaluation of Centromere-Associated DNA Sequences From a Marsupial (Macropodidae:Macropus rufogriseus) X Chromosome

“…Unequal crossover has been suggested to explain sex chromosome-specific amplification of constitutive heterochromatin seen in rodents (Nova et al 2002). The marsupial X and Y do not undergo homologous pairing (side to side) at meiosis; however, axial pairing (end to end) does occur (Solari and Bianchi 1975;Sharp 1982;Page et al 2003).…”

“…By virtue of their limited opportunity for recombination, the sex chromosomes of some mammals have large amounts of constitutive heterochromatin (Hayman and Martin 1974;Nova et al 2002;Kim et al 2004). The mammalian X chromosome has a high degree of genic conservation while having a highly labile arrangement, attributable in part to intrachromosomal rearrangements (Graves 1995;Waters et al 2001).…”