SEX DETERMINATION — A SUGGESTION. 5 



SEX DETERMINATION— A SUGGESTION. 



By Ruth C. Bamber, M.Sc. (Mrs. Bisbee). 

 Zoology Department, University of Liverpool. 



(Read March 10th, 1922.) 



No hypothesis so far put forward to account for sex- 

 determination is entirely satisfactory. The most widely 

 accepted view is that the X chromosome is the sex determiner, 

 and this is very strongly supported by cytological evidence. 

 There are, however, several serious difficulties to be faced. 

 In the first place many cases are known where the sex ratio 

 of the offspring is upset by that parent which, according to 

 cytological evidence, is not responsible for the determination 

 of sex at all. For example, in man, where haemophilia 

 is sex-linked in the male, transmitting women have on an 

 average more sons than daughters ; and in cats where the 

 yellow colour is sex-linked in the male, the transmitting 

 females have more male than female progeny. 1 Then, in 

 cattle 2 there is considerable evidence that the length of time 

 allowed to elapse between ovulation and fertilization affects 

 the sex ratio, early fertilization giving a preponderance of 

 females. It seems as though in these cases the female parent 

 in some way influences the sex of the offspring in spite of the 

 fact that it is the male which possesses the odd X chromosome. 

 Another and greater difficulty arises in connection with the 

 production of unisexual families under circumstances which do 

 not allow of an explanation on the hypothesis of selective 

 maturation or selective death rate. Riddle/ 5 by crossing 

 different genera of pigeons and causing them to " over- work 

 at egg production" obtained nearly all males in Spring, and 

 nearly all females in the Autumn of the same year. Harrison 4 

 and Goldschnlidt/ , by crossing different races of mot lis have 

 separately obtained intersexes, and in extreme cases, uni- 



