n2 



Procrcdiiif/s of Tiidutiia Academy of i^ncnce. 



females produce non-crossover j^ametes (1) p v) and (B 1' V) jiiid crossover 

 gametes of the composition b P V — Bpv — bpV — BPv — bPv and Jipv. The 

 males to which they are mated produce gametes of the composition b p v. 

 The different classes realized are given in table XX. 



Table XX. Classes realized on back crossing the bpv cf to the 

 hybrid 9 of composition bpv BPV. 



VI. Summary. 



The independent origin of curved, a wing mutant identical with 

 the one reported by Bridges, is liere given. Tlie data obtained 

 witli the various crosses is in agreement with the great mass of evi- 

 dence which shows that the chromosome conception of inheritance offers 

 the only rational basis upon which such data can be interpreted. Genes 

 carried by different chromosomes give free assortment with Mendelian 

 ratios, those in the same chromosome show linkage with no crossing over 

 in tlie male. 



It is evident that the factor grouping of a new mutant can be determined 

 by the failure of the double recessive to appear in the F., generation. Mor- 

 gan has made use of black-pink flies for testing a new mutant type. Black 

 is in the second group and pink in the third. If tlie new factor belongs to 

 either of these groups it will fail to show the double recessive among the 

 grandchildren from the cross. The sex relations from such an exjieriment 

 will readily determine whether or not it belongs to the sex-linked group. 

 If it belongs to none of these groups it is by exclusion placed in the fourth 

 group. 



