NON-CRISS-CROSS INHERITANCE IN DROSOPHILA 



MELANOGASTER. 



LILIAN V. MORGAN. 



A complete reversal of the ordinary criss-cross inheritance of 

 recessive sex-linked characters occurs in a line of Drosoplnla 

 recently obtained. ' In ordinary sex-linked inheritance the recessive 

 sex-linked characters of the mother are transmitted to the sons, 

 while the daughters show the dominating allelomorphic characters 

 of the father. In the present case the daughters show a recessive 

 sex-linked character of the mother and the sons show the dominat- 

 ing allelomorphic character of the father. The reversal is explica- 

 ble on the assumption that the two X-chromosomes of the mother 

 are united and behave at reduction as a single body. Sections 

 show that the eggs of these females do have two united X-chromo- 

 somes; the cytological evidence verifies the genetic deduction. 



A female fly (Fig. i, a), which was a somatic mosaic, showing 

 different sex-linked characters in the anterior and posterior parts, 

 appeared in a pair culture of which the parents had the following 

 constitution: one X of the mother -carried the differentials for 

 eosin, cut and forked; the other X carried the differentials for 

 forked and bar. She was therefore forked, heterozygous bar, and 

 gray. The X of the father carried the differential for yellow body 

 color, and he was therefore yellow. 



The head and thorax of the mosaic (Fig. i) were gray and the 

 eyes were slightly bar, while the abdomen was yellow ; the fly was 

 entirely female, having heterozygous bar eyes, no sex-combs, and 

 normal female genitalia. She was not virgin, but nevertheless was 

 isolated and mated to a black male, and produced 43 daughters and 

 59 sons. The daughters were, without exception, all yellow and 

 the sons were all gray, and all the offspring had wild type eyes 

 i.e., none were bar except two sons that were also forked and will 

 be considered later. The conclusion was at once evident that the 

 mosaic fly had received from its father two yellow-bearing chromo- 

 somes, inseparable from one another, and that these inseparable 



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