GENE FOR FOURTH CHROMOSOME OF DROSOPHILA 



333 



TABLE 4 



Here practically the only irregularity not due to chance is obvi- 

 ously caused by a deficiency (low viability) of pink flies of all 

 classes, and by a lower viability of males than of females. * The 

 independent assortment of bent with respect to the other factors, 

 and of the other factors with respect to each other, is best brought 

 out (especially in a case involving differential viability) by a tabu- 

 lation of the percent of cases inwhichany two pairs of factors, con- 

 sidered by themselves, underwent recombination in the formation 

 of the germ cells of the heterozygous parent. Thus, in the case of sex 

 and bent, the factors for sex and for bent in the heterozygous male 

 parent were both derived from the mother, the Y-chromosome and 

 the normal allelomorph of bent ('straight') both coming from the 

 father. Yet in the segregation division by which the sperm were 

 formed, a recombination occurred as frequently as a persistence 

 of the old combination, so that as many eggs were fertilized by 

 sperm bearing the sex factor and straight, or the Y-chromosome 

 and bent, as were fertilized by sperm with sex and bent or Y and 

 straight. As a result, straight females and bent males formed 50 

 per cent of the total number, as we should expect on the basis 

 that the factors were in non-homologous chromosomes which were 

 assorted independently. The other per cents of recombination 

 were as follows: 



per cent 



Sex-black 50.0 



sex-pink 55 . 



black-pink 50 . 5 



black-bent 50.5 



pink-bent 49 . 



In a reciprocal cross some of the triply heterozygous Fi females 

 were back-crossed to triply recessive males. Here, too, we should 



