296 



CALVIN B. BRIDGES 



crossover value was 35, which showed that streak is so far to the 

 left of purple that only an approximate calculation of its position 

 could be made from the data. In a region of such length the 

 correction to be supplied because of double crossing over is 

 quite large and correspondingly inexact. On the basis of data 

 that have since become available it appears that there is about 

 37.3 per cent of crossing over between streak and purple. Purple 

 has played an important role in the mapping of several other 

 genes, the details of which will appear in accounts of these 

 mutations. 



A SUMMARY OF THE LINKAGE DATA INVOLVING PURPLE 



. Besides the data reported in this paper, there are available 

 data from four other principal papers — Bridges' study of age 

 variation in crossing over (Jour. Exp. Zool., '15), MuUer's study 

 of crossing over by means of the progeny test (Am. Nat., '16), 

 Plough's study of temperature variations in crossing over, and 

 the data given in various sections of a Carnegie publication by 

 Bridges and Morgan that is soon to appear. Table 20 gives the 

 totals for all these data collected according to two loci calcu- 

 lations. The black purple crossover value of 6.2 based on 48,931 

 flies places the locus of purple at 6.2 units to the right of black, 

 or at 52.7 when referred to star as the zero point. 



TABLE 20 



.4 summary of the purple crossover data 



Star purple 



Streak purple... 

 Dachs purple. . . 



Black purple 



Purple vestigial 

 Purple curved. . 

 Purple plexus. . . 



Purple arc 



Purple speck . . . 

 Purple balloon. 



8,155 



2,665 



1,489 



48,931 



13,601 



51,136 



344 



2,625 



11,985 



462 



CROSSOVERS 



3,561 



883 



293 



3,026 



1,609 



10,205 



164 



1,066 



5,474 



218 



PER CENT 



43.7 

 33.1 

 19.7 

 6.2 

 11.8 

 19.9 

 47.7 

 40.6 

 45.7 

 47.2 



