Increases and decreases of whole-arm heterochromatin in specific chromosomes: an extraordinary situation in hybrids of the Mus terricolor complex.
The three chromosomal species of Mus terricolor display fixed variations in the short-arm heterochromatin of autosomes 1, 3, and 6. Some laboratory-generated hybrids among the chromosomal species show an unusual increase or decrease in the extent of whole-arm heterochromatin, instead of the expected heterozygosity for the heterochromatic short arms. The whole-arm increase/decrease tends to favor homozygosity for the presence or absence of the heterochromatic short arms. Interestingly, this increase/decrease conforms with the karyotypes of the parental chromosomal species. Although rapid karyotypic changes have been reported in other plant and animal hybrids, the situation observed in the M. terricolor hybrids is unique. The changes are stable and could be a product of the unusual chromosomal organization of recombinogenic telomeric sequences in this species complex. The altered karyological constitution is constant in both somatic and germ cells of each hybrid, suggesting that the changes occurred early in their development. The high frequency and nonrandom recurrence of similar changes in different hybrids seem to reflect a mechanism that might have been instrumental in the fixation of these chromosomal variations in a stable homozygous condition in natural populations.
Sharma
T
T
Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi, India. tsharma@banaras.ernet.in
Bardhan
A
A
Bahadur
M
M
D000818:Animals; D002874:Chromosome Mapping; D006570:Heterochromatin / Q000235:genetics*; D007621:Karyotyping; D051379:Mice / Q000235:genetics*; D008957:Models, Genetic; D009693:Nucleic Acid Hybridization
D006570:Heterochromatin