CHROMOSOMES OF THE MEXICAN PLATEAU MOUSE, PEROMYSCUS MELANOPHRYS, AND A NEW SEX DETERMINING MECHANISM IN MAMMALS

Abstract

A chromosomal analysis of 86 specimens of Peromyscus melanophrys reveals a unique type of chromosomal difference between males and females Females possess three large pairs of subtelocentric autosomes, two pairs of small submetacentric autosomes, and 18 pairs of acrocentric autosomes. The X chromosomes are also subtelocentric. Males possess a similar karyotype with a subtelocentric X chromosome, a minute Y chromosome, and two unmatched autosomes, a large subtelocentric and a large acrocentric. Both sexes have a diploid number of 48. Studies from meiosis and autoradiography indicate that a portion of the original Y chromosome has been translocated to an autosome resulting in a new multiple sex determining mechanism in mammals, an X1X1X2X2/X1X2Y1Y2 system.