146 



HEREDITY AND ENVIRONMENT 



by a sperm with 23 chromosomes an individual 

 with 47 chromosomes, or a male, results 



(Fig. 37). 



Fig. 37. Diagrams of Sex Differentiation in Man. A, 

 spermatogonium with 47 chromosomes one of which (sinall 

 circle) is the X chromosome. B, spermatocyte showing 23 syn- 

 aptic pairs and a single unpaired X chromosome. C, reduction 

 division in which the synaptic pairs separate while the Z 

 chromosome does not divide, consequently the second sper- 

 matocytes D and D' contain respectively 23 -|- Z and 23 

 chromosomes. E and E', second maturation division in which 

 every chromosome divides, giving rise to two equal classes of 

 spermatids and spermatozoa, one of which has 24 chromo- 

 somes and the other 33. If an egg containing 24 chromo- 

 somes is fertilized by a sperm with. 24, a female with 48 

 chromosomes is produced; if an egg with 24 chromosomes is 

 fertilized by a sperm with 23, a male with 47 chromosomes 

 results. (From Morgan after Winiwarter.) 



