ENVIRONMENTAL EFFECTS 



duced in the sperm are just as lethal to the 

 biparental males as to the females (P. W. 

 Whiting, 1933a, b). 



If females are treated and subsequently mated, 

 there is no appreciable reduction in male ratio, 

 indicating that few, if any recessive lethals 

 are induced in the egg. While treatment of 

 mated females causes a radical lowering of fe- 

 male ratio indicating that more dominant lethals* 

 are induced in the sperm than recessive lethals) 

 in the egg. It has also been noted (P.W. Whit- 

 ing, 1929a; N. C. Bostian, 1931) that the per- 

 centage of female offspring from X-radiated 

 .mothers, mated previous to treatment, is marked- 

 ly decreased (Greb, 1933). 



P. W. Whiting ( 1937a) demonstrated that treat- 

 ment of sperm with X-ray dosages of 20,000, 

 40,000, and 75,000 R units produces at least one 

 dominant lethal in every sperm cell. No daugh- 

 ters occur in the progeny and the average number 

 of males produced per day does not equal that 

 to be expected from virgin females, indicating 

 that many eggs are fertilized and die. Sperm 

 treated with 75,000 R units fertilized almost 

 as many eggs as untreated sperm; therefore, the 

 treatment apparently did not cause inactivation. 

 However, a slight increase in the average males 

 per day from mates of males treated with 75,000 

 R units as compared with those from mates of 

 untreated controls suggested the possibility 

 that spermatogenesis might to some extent be 

 stopped and sperm supply decreased. 



Thus partial male sterility results from dom- 

 inant lethals at relatively v/eak dosages, com- 

 plete male sterility results from dominant le- 



137 



