No. 644] MUTANT CHARACTERS IN DROSOPHILA 



237 



the X-chromosome of ivillistoni at present is only slightly 

 longer than the map of the melanog aster X-chromo- 

 some (84 as contrasted with 70 units), whereas the wil- 

 Ustoni X-ehromosome itself appears to be about twice the 

 length of that of melanogaster. This suggests that cross- 

 ing over is less frequent in willistoni than in melano- 

 gaster. 



SUMMAEY 



1. Twenty-eight recessive sex-linked mutant charac- 

 ters in Drosophila tvillistoni are described and their 

 linkage relations considered. 



2. In general, the genetic behavior of irUIistoni (as re- 

 gards crossing over, etc.) is similar to that of D. mela- 

 nogaster and the other species of Drosophila whose ge- 

 netic behavior is known. 



3. There is a strong indication of parallelism between 

 the mutants yellow and scute in willistom and yellow and 

 scute in melanogaster. 



4. In both species these characters are completely or 

 very closely linked. 



5. There is some indication of parallelism between the 

 characters forked and stubby in toillistoni and singed and 

 forked in melanogaster. 



6. In melanogaster the genes for yellow and scute are 

 located" at one end of the chromosome map, and 



singed and forked are 21 units and 56.5 units respec- 

 tively from this end. In ivillistoni yellow and scute are 

 near the middle of the map, and forked and stubby are 

 on one side at 12 units and 42 units respectively. 



7. Since the X-chromosome of melanogaster is short 

 and rod-like, while that of ivillistoni is approximately 

 twice as long and is V-shaped, this relation of the chro- 

 mosome maps suggests that the melanogaster X-chromo- 

 some corresponds to one arm of the Y-shaped X-chromo- 

 some of ivillistoni, with the locus of yellow correspond- 

 ing in the two cases. This agrees with the sn^irestion 

 made by Lancefield in the case of T). oh.^curn in whidi the 

 X-chromosomes resemble those of ivillistoni. 



