CHROMOSOME ANALYSIS AND MEIOTIC BEHAVIOR OF PEROMYSCUS TRUEI GRATUS

Resumen

In Peromyscus truei gratus from the Pedregal de San ángel (México, D. F.) the chromosome number is 2n=48, as has been found in other species, subspecies and populations of this genus. The chromosomic complement is very similar to the one found in Peromyscus truei proceeding from New Mexico (USA). In meiosis, 23 bivalents were observed in parallel; the sex chromosomes were found to assume a peculiar disposition, "in tandem", forming a X-Y complex with a very small pairing segment. The X-chromosome in pachythene takes a ring shaped form.