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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 (small 

 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 X 

 chromosome does not divide, consequently the second sper- 

 matocytes D and D' contain respectively 23 _|- X 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 23. 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.) 



