294 



GENETICS 



This Is most likely to occur when closely related individuals 

 are mated, just as the production of superior individuals is 

 most frequent when unrelated stocks are crossed. A large 

 number of recessive genes, defective in greater or less de- 

 gree, are scattered through a given species, usually producing 

 no detectable affects, because each is supplemented by a 

 normal, dominant gene in the same pair. These defective 

 genes are transmitted from parent to offspring, producing 



Figure 6i. Diagram to show how parents (P and M) manifesting 

 no personal defects may produce offspring (F) manifesting many 

 defects. Each parent has a single defective gene (white) in several 

 of his pairs, and these defective genes are in the same pairs in the 

 two parents. In consequence some of the offspring may receive two 

 defective genes in many pairs, as shown at F; these will manifest 

 many personal defects. 



no effect unless two of them get together. Two Individuals 

 that have recently come from the same ancestors (hence 

 "related") are likely to have received from these ancestors 

 the same defective genes in some of their pairs. When such 

 individuals are mated, to some of their offspring each may 

 contribute defective genes in the same pairs (figure 6i). 

 The result is the production of a defective individual, one 

 that shows weaknesses and abnormalities in various parts 

 or functions. Even from two superior parents, particularly 

 if closely related, there may be produced offspring that arc 



