THE CHROMOSOMES OF A POPULATION OF Microtus mexicanus (Muridae-Rodentia) OF CENTRAL MEXICO

Resumen

Chromosome analysis of a population of Microtus mexicanus mexicanus collected in the southern part of the Valley of Mexico was carried out. The chromosome source was a bone marrow cell suspension. The diploid number found was 48, with a fundamental number (number of autosomic arms) of 58 and a sexual
differentiation pattern of XX/XY. This species is polimorphic as far as the diploid number is concerned, as Matthey (1957) reported a karyotype with a diploid number of 44 from a specimen of a northern population. Two robertsonian fusions may have been the rearrangements involved in this particular type of karyotype variation. The karyological features of southern populations are probably primitive with respect to northern populations.