THE CELLULAR BASIS OF HEREDITY 



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pairs, leaving the X chromosome unpaired (Fig. 39, B) and in the re- 

 duction division the pairs separate, while the X chromosome goes entire 

 into one of the daughter cells, which consequently contains 23 -f- X 

 chromosomes, whereas the other daughter cell contains 23 chromosomes 

 (Fig. 39 C and D). The former gives rise to spermatozoa with 24 

 chromosomes, the latter to spermatozoa with 23 chromosomes. In the 

 female there are probably 48 chromosomes, according to Winiwarter, 

 there being two X chromosomes, one from each parent, and after the 

 reduction divisions every egg contains 24 chromosomes. If an egg is 

 fertilized by a sperm containing 24 chromosomes an individual with 48 

 chromosomes, or a female, is produced ; if fertilized by a sperm with 23 

 chromosomes an individual with 47 chromosomes, or a male, results 

 (Fig. 39). 



Fig. 39. Diagrams of Sex Differentiation in Man. A, spermatogonium with 

 47 chromosomes one of which is the " sex " chromosome. B, spermatocyte showing 23 

 synaptic paira aLd a single unpaired " sex " chromosome. C, reduction division in 

 which the synaptic pairs separate while the sex chromosome does not divide, conse- 

 quently the second spermatocytes D and D' contain respectively 23 + X and 23 chromo- 

 somes. E and E', second maturation division in which every chromosome divides, giv- 

 ing rise to two equal classes of spermatids and spermatozoa, one of which has 24 

 chromosomes and the other 23. If an egg containing 24 chromosomes is fertilized by 

 a sperm with 24, a female with 48 chromosomes is produced ; if an egg with 24 chrom- 

 osomes is fertilized by a sperm with 23, a male results. (From Morgan after Wini- 

 warter.) 



It must be said that other investigators, notably Guyer and Mont- 

 gomery, have not found 47 chromosomes in the spermatogonia of man, 

 but 23. Since both the latter investigators worked on negroes whereas 

 Winiwarter worked on white men it has been suggested quite recently 

 by Morgan and Guyer that there may be twice as many chromosomes 

 in the white race as in the black. A similar condition in which one race 

 has twice as many chromosomes as another race of the same species is 



