REVIEW OF BIOLOGY OF SEX-DETERMINATION 
3 
tocytes (fig. 1). We now know that the X-chromosome is 
paired in the female cells, both somatic and germinal. In 
Diploid Group, Hale Diploid Group , Female 
Fig. 1. Simplest Known Mechanism of Sex-Determination 
The X-chromosome is shown as black; the autosomes are in outline 
spermatogenesis the autosomes pair to form tetrads. In the 
first spermatocyte division the tetrads are reduced to dyads and 
the X-chromosome generally passes undivided to one second 
