MENDELIAN INHERITANCE 



225 



teristics, that the main conclusions of Mendel are now univer- 

 sally accepted. Many characters, however, do not seem to seg- 

 regate or Mendelize, at least not in any simple way that 

 can be predicted, and these are the problems that modern 

 experimentalists are working on. 



PARENTS 



FIG. 97. Diagram illustrating Mendelian inheritance when two character- 

 istics are involved. A yellow-round and a green-wrinkled pea are crossed. The 

 Fi generation gives only yellow and round peas, these being dominant over green 

 and wrinkled. These when inter-bred segregate out in the proportion of 

 9:3:3:1. (From Morgan.) 



C. HEREDITY OF SEX. Cytological evidence. Sex, with 

 many of the secondary characters which go with it, is recognized 

 today as an aggregate of Mendelian characteristics. The 

 evidence on which this generalization is based is partly cytolog- 

 ical, partly experimental, and while many perplexing problems 

 connected with sex are still unsolved, the evidence in favor of 

 the heredity of sex is so strong that it may be accepted as the 

 most plausible working hypothesis at the present time. 



On p. 215 reference was made to divergent results in regard 



