6 SOME POSSIBLE HEARINGS OF GENETICS ON PATHOLOGY 



It is popularly supposed that if a trait is dominant it will be 

 expected to spread more widely in the race than will a recessive 

 character. This is owing largely to a verbal confusion. Col- 

 loquially we think of dominance as meaning spreading. A domi- 

 nant nation, for example, is one that is spread widely over the face 

 of the earth. But a Mendelian dominant should carry no such 

 implications. A dominant gene, if crossed into a race, will stand 

 the same chances of being lost as a recessive gene, Fig. 3. 



The situation is similar in many ways to the inheritance of 

 surnames in any human population. A new surname introduced 

 is likely to disappear after a few generations. There is a bare 

 chance, however, that it may spread. 



Fig. 3. Mating of short-fingered and normal individual (the short-fin- 

 gered character is dominant), giving in F, normal and short-fingered individ- 

 uals in equal numbers. If the latter is out-bred to normal again, half the 

 next generation is normal and half short-fingered. 



