OF MUTANT CHARACTERS. 



277 



The lines of selected flies which show neither vestigial nor nick for 

 some generations should be pure for the nick gene. This method was 

 somewhat rough, but since it offered a means of carrying on the stock 

 without extra work it was employed. 



Some black nick males - - were crossed to vestigial females 



o v g 



in the course of some later experiments, and these gave the same sort 

 of result as that noted in the first division of table 124, except that 

 there was found to be a marked sex-limited development. While 

 82 per cent of the vestigial-nick female compounds showed the nick 

 character, only about half of this percentage (45 per cent) of the 

 males showed the nick character (table 124, last division). This sex- 

 limitation is in the opposite direction from that previously known in 



the case of the vestigial-antlered compounds ( J- ) , for there most of 



\ V g / 



the compound males showed the antlered, while only a few of the 

 females were like antlered. 



DACHS-LETHAL (</,). 

 ORIGIN OF DACHS-LETHAL. 



The first demonstration 1 of a recessive autosomal lethal in Dro- 

 sophila came through the effort to determine more closely the locus 

 of star by means of its linkage relations to dachs (October 6, 1915, 

 culture 2217). 



TABLE 125. Pi, star 9 X dachs cf; FI star 9 + 



star 



The back-crosses which furnished the bulk of these data have already 

 been given in the section on star; in addition some F 2 cultures from 

 the cross of star by dachs were raised by inbreeding FI star males and 

 females (table 125). It is comparatively rare that an F 2 culture is 

 raised under such circumstances, since in general the back-cross is so 

 much more efficient. In this case the F 2 's were raised as an example 

 of the lethal effects of homozygous star in combination with the link- 

 age ratios. Because of the fact that all homozygous stars die, the F 2 



1 In the case of the aberrant ratios of pink, Liff (15) had suggested that an autosomal lethal 

 might be the explanation. 



