THE GENETICS OF HABROBRACON JUGLANDIS ASHMEAD 



mata are the ones which tend to be permanent, 

 these would necessarily result in large (and 

 therefore dominant) terminal deletions. Dele- 

 tions small enough to act as recessives might 

 not have a lethal effect on the haploid embryo 

 until after hatching and therefore would not be 

 detected with methods used in present work. In 

 the limited tests made with fertilized eggs it 

 is also possible that a few deficiency hetero- 

 zygotes surviving would not noticeably affect 

 hatchability ratios. 



Genetic literature includes much discussion 

 of lethal factors. In Habrobracon the occur- 

 rence of dominant lethals in the sperm can be 

 readily distinguished from direct killing of the 

 male gametes. The most striking result of X-ra- 

 diation of males is, however, the production of 

 sterility (or partial sterility) of a second 

 type. In this case the sperm are not inactivat- 

 ed but are fully capable of fertilizing the eggs. 

 Such fertilized eggs, however, do not hatch be- 

 cause the sperm have a dominant lethal effect. 

 Females mated to males with this type of steril- 

 ity produce azygous sons only and in numbers 

 equal to those produced by females mated to nor- 

 mal males; in other words, although they produce 

 no females, as the result of dominant lethal ef- 

 fects of the sperm which have entered the eggs, 

 they behave like mated rather than unmated fe- 

 males in respect to number of azygous sons. 

 Habrobracon, then, is especially well suited for 

 separating dominant lethal male sterility from 

 sterility resulting from inactivated sperm on 

 the basis simply of numbers of azygous sons pro- 

 duced by females mated to the males to be tested 

 (P. W. Whiting, 1938a, b). 



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