CHROMOSOMES AND SEX 



379 



The number of chromosomes in man and the make-up of the comple- 

 ment in the two sexes have long been subjects of controversy.'^^ It has 

 now been established that there are 24 pairs represented in the comple- 

 ment. According to most recent workers (Painter, Evans and Swezy, 

 Kemp), these include an XF pair in the male and XX in the female; 

 but others (de Winiwarter, Oguma) contend that there is no Y, the sex- 

 chromosomes being of the XO type. In Painter's material there can be 

 little doubt that a large, unequal pair resembling XY pairs in other 

 mammals is present and disjoins in / (Fig. 213). 



B 



D 



jn 



Fig. 213. — A, diploid chromosome complement in man. B, metaphase I in spermato- 

 cyte, showing XY pair about to disjoin. C, the X and Y have disjoined and passed to 

 poles in advance of autosomes. D, XY pairs in opossum, monkey, and man. {After 

 Painter, 1923o, 1922a.) 



There is considerable evidence for the view that the XO type has been 

 derived from the XY type through loss of the Y. In different organisms 

 many stages in the supposed decrease in size and restriction of function 

 on the part of the Y are known. Moreover, the Y may be either present 

 or absent in Metapodius, and such an explanation has been suggested 

 for the divergence of opinion regarding man (Wilson, 19096, 1925). 



In all of the foregoing cases it is the male which is "digametic," 

 or "heterogametic," sperms of two kinds fertilizing eggs of one kind. 

 In some groups, notably birds, moths, and butterflies, the female is 

 digametic. Here the sperms are all alike, while the eggs are of two 

 sorts. (In such cases the sex-chromosomes are often referred to as Z and 

 W instead of X and Y.) 



" Reports on the chromosomes of man have been made by many investigators, 

 among whom may be mentioned Flemming (18826, 1898), Moore and Arnold (1906), 

 Duesbcrg (1906), Guyer (1910), Gutherz (1912), Montgomery (1912), de Winiwarter 

 (1912, 1921a6), Wieman (1917), Evans (1918), Painter (1921o, 1922a, 1923o, 1930), 

 Grosser (1921), Rappeport (1922), Oguma and Kihara (1922, 1923), de Winiwarter 

 and Oguma (1925, 1926), Oguma (1930), Kemp (1929), Evans and Swezy (1928, 

 1929). 



