The Cytogenetics of the Male Germ Cells and the Testis in Mammals

Abstract

The testis was the classical source of material for chromosome study in mammals. The first objectives were the determination of chromosome number, the identification of the sex chromosomes and the characterization of the normal course of meiosis in spermatocytes. Later, chiasma counts, the analysis of meiotic behavior in structural heterozygotes and mapping the distribution of chro-momeres in pachytene with a view to the recognition of individual bivalents were all attempted. These latter tasks are barely more than begun even today. However, cytogenetic methods can contribute in a different way to an understanding of some aspects of testicular biology, the main operational theme being the identification of specific cell types in a mixed population by specific features of the karyotype. Four of these aspects are considered below.