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Heredity and Environment 



(3 GAMETES | 



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) 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 729 genotypes only 4 of which are shown in the 

 diagram. 



