OF MUTANT CHARACTERS. 237 



CHROMOSOME CARRYING APTEROUS. 



Metz crossed an apterous male to a vermilion female and, as ex- 

 pected, the apterous character and vermilion showed no linkage in F 2 . 

 The total offspring from pair matings in this line was 1,498 wild-type 

 to 369 apterous, or 19.8 per cent, which is a poorer viability than 

 before, but not as low as in the sister culture raised en masse. The 

 mass-cultures gave only 699 apterous among 4,539 offspring, and the 

 low percentage (15.4) is the result of the crowding that always occurs 

 in mass-cultures. 



An apterous female was successfully crossed to a pink male and 

 there were produced in F 2 402 wild-type, 114 apterous, 111 pink, and 

 34 apterous pink flies, which is an approach to a 9:3:3:1 ratio and 

 proved that apterous was not third-chromosome. 



No successful mating of apterous by black was made, so that flies 

 heterozygous for apterous had to be used in the PI instead. From 

 FI pairs, heterozygous for apterous in both parents, there were pro- 

 duced 414 wild-type, 136 apterous, 155 black, and black apterous 

 flies. This 2:1:1:0 ratio demonstrated that apterous is in the second 

 chromosome. 



LOCUS OF APTEROUS. 



In determining the locus of apterous, Metz took advantage of the 

 fact that flies heterozygous for black are darker than the wild-type, 

 that is, he classified black as a dominant as well as a recessive character 

 in F 2 . In the above F 2 from the cross of apterous (heterozygous) to 

 black, Metz observed no apterous flies that seemed to be heterozygous 

 for black and correspondingly no long-winged flies that were not 

 heterozygous for black. While this classification can not be accurate, 

 it is nevertheless certain that if very many such cross-over flies had 

 been present this fact could have been noted. The locus of apterous 

 is therefore not far from that of black in the second chromosome. 



APTEROUS BY REMUTATION. 



In working with the eosin modifier "cream c" Bridges found a 

 mutant character which in appreance agreed at every point with the 

 previously known apterous (cultures 5588, 5631, October 16, 1916). 

 This experiment, in which apterous reappearance had come from the 

 PI mating of the original cream c female (found in eosin stock) and a 

 star-dichaete male (dichaete is a third-chromosome dominant). The 

 FI mating had been of (eosin) star-dichaete sons and wild-type daugh- 

 ters in pairs. The apterous character appeared in 63 individuals 

 (males and females equally numerous) in a total of 449 in two separate 

 cultures (5588 and 5631). The percentage of apterous w r as thus only 

 14.0, which indicates a rather poorer viability than was shown in the 

 culture of Metz. 



