1 62 Heredity and Environment 



thumb, from one hand while all females have the full number 

 on both hands. When the hands (gametes) are struck together 

 as in the game of "bean porridge" there will be an equal number 

 of cases in which a hand with five digits meets one with five 

 (female) and one with four meets one with five (male). In the 

 latter case there will be an "odd" thumb (chromosome) which 

 has no mate. 



Sex- Determination in Man. Even in man sex is determined in 

 the same manner, according to several recent investigators. Wini- 

 warter concluded that there are in the spermatogonia of man 47 

 chromosomes, one of which is the X or accessory chromosome. 

 These unite in synapsis into 23 pairs, leaving the X chromosome 

 unpaired; in the reduction division the pairs separate, while the 

 X chromosome goes entire into one of the daughter cells, which 

 consequently contains 23 -{- X chromosomes, whereas the other 

 daughter cell contains 23 chromosomes. In the female there are 

 probably 48 chromosomes, there being two X chromosomes, one 

 from each parent, and after the reduction divisions every egg 

 contains 24 chromosomes. Winiwarter held that 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. 



It is a curious fact that it has been very difficult to determine 

 the exact number of chromosomes in man. This is probably due 

 to the difficulty of preserving in an unaltered condition the chro- 

 mosomes of mammals in general, as McClung and his pupils have 

 shown, and also to the peculiar difficulty of obtaining human tis- 

 sues in a perfectly fresh and normal condition. Thus Guyer and 

 Montgomery found not 47 but about 22 chromosomes in the 

 spermatogonia of man. Since both the latter investigators 

 worked on negroes whereas Winiwarter worked on white men it 

 was suggested by Morgan and Guyer that there may be twice 

 as many chromosomes in the white race as in the black. A 



