Cytological studies in the cycads: sex chromosomes in Cycas

Abstract

The chromosomes of Cycas pectinata are studied from root tip and pollen mitoses. The male and female plants showed the same number of chromosomes (2n = 22) with almost identical chromosome morphology. The only difference is that in the female plant two chromosomes of the somatic complement (pair III) bear satellites, while in the male the same pair is heteromorphic with only one of its members bearing a satellite. This becomes further clear when two types of haplid complements are noticed in pollen mitosis, one type possessing a satellited chromosome, and the other showing none bearing a satellite. The pair of chromosomes which is heteromorphic in the male is assumed to be associated with sex determination in Cycas, the male being the heterogametic sex with XY type of sex chromosomes.