Vol. XXVI. April, 1914. No. 4 



BIOLOGICAL BULLETIN 



NO CROSSING OVER IN THE MALE OF DROSOPHILA 



OF GENES IN THE SECOND AND THIRD 



PAIRS OF CHROMOSOMES. 



T. H. MORGAN. 



In a brief note in Science for November 22, 1912, it was pointed 

 out that there was no "crossing over" in the male between the 

 factors for black body color and vestigial wings, while between 

 the same factors in the female there was 22 per cent, of cross- 

 ing over. The data then published have been extended and re- 

 vised, 1 and the results can now be given in detail. For purposes 

 of easy comparison I shall present the data in the same order as 

 those given in the preliminary report. 



It had been shown by Morgan and Lynch (BiOL. BULL., 

 XXI 1 1., 1912) that when black flies having normal (long) wings 

 are mated to gray flies having vestigial wings, only three classes 

 appear in 2, viz. : 



Gray Long. Black Long. Gray Vestigial. Black Vestigial. 



4569 2151 1626 o 



It was pointed out later (Science, 1912) that the absence of 

 the black vestigial class would be expected, if, in FI, no interchange 

 of factors occurs in one sex. The following analysis will make 

 evident why, on the assumption that there is no crossing over in 

 the gametogenesis of the FI male, there are no black vestigials 

 expected in F 2 . 



1 We have learned better how to control the conditions of culture so that less 

 disturbance results from differential viability. Many of the old data, although 

 consistent within themselves, are not strictly comparable with the recent data 

 obtained under better conditions. For the case of black and vestigial the data 

 presented here differ from those reported (Science, 1912) in that new data have been 

 substituted for some of the old data in the tests of the amount of crossing over in 

 the female. 



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