118 



ORIGIN OF SOMATIC 



When a black male is mated to a yellow female, the 

 female kittens are tortoise-shell as before, but the 

 males yellow. The Mendelian hypothesis which 

 explains these results is that the male is alwa^^s 

 heterozygous, or has only one colour factor whether 

 yellow or black, and transmits these colours only 

 to his daughters, while the female has two 

 colour factors, either BB, YY, or BY, Thus the 

 crosses are: — 



yocS 



TOfirO/SJE-SHELL Q 



BO(S 



BLACkC O 



BLACK O 

 BO 6 



reiLOivQ 



BXQ 



ropro/S£SH£LL Q 



Yo6 ^ 



YELLOW O 



The sex must be determined therefore by the 

 spermatozoa, as in the case of colour-blindness, etc., 

 in man, and the colour factor must always be in the 

 female-producing sperm. 



