The Cellular Basis 



175 



1 9 GAMETES | ZYGOTES | 6 GAMETES I 



FIG. 58. DIAGRAM SHOWING SOME OF THE POSSIBLE DISTRIBUTIONS OF 

 CHROMOSOMES OF GRANDPARENTS TO GRANDCHILDREN. Chromosomes of 

 maternal grandfather shaded black, of maternal grandmother with 'cross 

 lines; of paternal grandmother stippled, of paternal grandfather un- 

 shaded. "Sex-chromosomes" are /-shaped, a pair being present in the 

 female, a single one in the male. In the maturation of oocyte and of sper- 

 matocyte homologous chromosomes unite in pairs and then separate into 

 the gametes. With 6 pairs of chromosomes, each free to separate in 2 

 directions the largest possible number of combinations in the gametes is 

 (2) 6 or 64 and since any sperm may unite with any egg, the number of 

 combinations possible in the zygotes is (64) 2 or 4096 and, excluding all 

 duplications, there are (3) 6 or 729 genotypes only 4 of which are shown 

 in the diagram. 



