318 Cell as Basis of Organic Activity 



about which any real objective information can be obtained are compara- 

 tively simple ones such as eye color, right- or left-handedness, hemo- 

 philia, red-green color blindness, or obviously abnormal ones. This 

 latter group includes such things as extra fingers, feeble-minded- 

 ness, syndactyly (joined fingers), scaly skin, dwarfism, etc. Very 

 often these abnormalities appear in isolated communities where a great 

 deal of inbreeding has occurred, and their recessive nature can then 

 be determined. In populations where intermarriage between unrelated 

 groups is most common, the abnormalities which appear are most fre- 

 quently dominant ones. 



Some inherited human characters whose genetics is understood are 

 as follows : 



Character How Inherited Nature 



Left-handedness A single gene Recessive to right-handedness 



Hemophilia Sex-linked, single gene Recessive to normal 



Polydactyly Single gene Dominant to normal condition 



(extra digits) 



Albinism Single genes Recessive to normal 



Feeble-mindedness At times single genes Recessive to normal 



Red-green color Sex-linked, single gene Recessive to normal 



blindness 



