538 GENETICS IN RELATION TO AGRICULTURE 



the sex-factors. In man cytological investigations have been made 

 by Guyer, Montgomery, von Winiwarter, Wiemen and Evans. 1 The 

 evidence is very conflicting as regards total chromosome number, but it 

 is not at all in conflict with the hypothesis of an XY type of sex inheri- 

 tance in man. Von Winiwarter finds that there are forty-seven chromo- 

 somes in the male. In the formation of spermatozoa he observed that 

 half received twenty-three and half twenty-four chromosomes. In the 

 female his evidence pointed to forty-eight as the somatic number, con- 

 sequently it may be assumed that all egg-cells normally contain twenty- 

 four chromosomes. The observations of Guyer and Montgomery which 

 were made with material from the negro, seem to indicate that the chro- 

 mosome number in this race is one-half that in the white race. This 

 evidence also indicated that a pair of accessory chromosomes exist in the 

 male, but the evidence is not conclusive. The existence of an X and a F 

 chromosome in the male has been claimed by Wieman. The cytological 

 evidence, therefore, so far as it goes, indicates that there is nothing in 

 the internal mechanism of mammals in conflict with the belief that the 

 female is homozygous for a" sex-factor, and the male heterozygous. 



The evidence from hereditary phenomena is not very extensive for 

 domestic mammals. In man, however, as has been pointed out in other 

 places, a number of sex-linked characters are known, and these follow 

 the XY type of sex-determination. Here the evidence is strong enough 

 to be conclusive, but in no domsetic animal with the exception of the cat 

 is any sex-linked character known. In the cat the characters in question 

 are black, orange, and tortoise-shell coat colors. According to Ibsen's 

 analysis of the case, which appears to be most satisfactory, there are two 

 factors giving the following color classes and formulae: 



' Females Males Classes 



The experimental evidence as to the relation of the colors has been dis- 

 cussed by Doncaster, Little, Whiting, and Ibsen, but the analysis is still 

 in debate. Such as it is, however, there is no room for doubt that sex- 

 linked characters occur in the cat and are distributed in accordance with 

 the accepted conclusion that the male is heterozygous for sex and the 

 female homozygous. 



1 Dr. Herbert M. Evans of the University of California. Data not published, but 

 in the case of a white man hundreds of counts give constantly 48 chromosomes in the 

 spermatogonia. If the number in the white male is 48, instead of 47 as von Wini- 

 warter concluded, it would indicate the existence of a F element as well as one X 

 element in the male. 



