The chromosomes of Metachirus nudicaudatus (Marsupialia : Didelphidae)

Abstract

A karyologic study of M. nudicaudatus, carried out on three females and five males, shows a chromosome number of 14, with apparent lack of dimorphism in the sex chromosomes. Nevertheless, the heterochromatin staining technique reveals the Y chromosome to be fully heteropycnotic. The meiotic chromosome has a sex vesicle at the pachytene stage. The similarity of this karyotype with those of Caluromys derbianus and Dromiciops australis is striking, especially considering that the genera belong to two subfamilies separated early in their evolutionary history. Our results support the opinion of Hayman and Martin that the original chromosome number in Marsupialia was 14.