GENES IN THE MALE OF DROSOPHILA. 



203 



Again the results conform. Here the two dominants entered 

 from one side and two recessives from the other, and the double 

 recessive normal black was used for testing the gametes of the 

 FI male. Streak lies at the most extreme end of the chromosome 

 so far as known, on the same side of black as does dachs, and on 

 the other side from purple, vestigial and arc. The interval be- 

 tween streak and black is nearly as long as that between black 

 and arc, so that the results are of interest because the whole 

 section from streak on the one hand to arc on the other is known 

 to give the same result, namely, a complete absence of crossing 

 over. These two loci, streak and arc, are so far apart that in 

 the female there is practically free Mendelian assortment. 



No CROSSING OVER IN THE MALE BETWEEN GENES IN THE 

 THIRD PAIR OF CHROMOSOMES. 



A test of whether or not crossing over takes place in the male 

 between genes in the third group; or, as we say, in the third 

 chromosome, was first published for the case of pink and ebony 

 by Sturtevant (Science, 1913), who showed that no crossing over 

 occurred in the FI male for the small number of males tested. 

 The following case gives similar results for another pair of loci. 

 The data are taken from experiments that are being carried out 

 by C. B. Bridges and the author. 



A mutant stock has kidney-shaped eyes. A double recessive 

 stock of pink kidney was made up, both factors being in the 

 third chromosome. Pink kidney mated to wild flies gave FI 

 flies with red round eyes. The FI males back crossed to pink 

 kidney females gave the following results: 



