A 



r 



B 



r 



e 



C 



"\ 



Figure 31. Diagrams to illustrate the suggested explanation of the 

 various different results of placing together two defective chromo- 

 somes. The diagrams represent three cells, each containing a pair of 

 chromosomes, each chromosome composed of two parts. A, The two 

 defects (e and v) in different parts of the two chromosomes, so that 

 there is present a normal part corresponding to each defective part. 

 Result, the individual is normal. B, The two defects (e) of the same 

 kind, and present in the same part of the two chromosomes, so that 

 no corresponding normal part is present. Result, the individual mani- 

 fests the defect e. C, Two different defects (e and b), present in 

 the same part of the two chromosomes, so that no corresponding 

 normal part is present. Result, the individual is defective (usually 

 intermediate between the two defective conditions, but one defect 

 sometimes prevailing over the other). 



135 



