1 8 GENETIC VARIATIONS 



is dominant, one recessive. The two members may differ (in 

 diverse cases) in many gradations of effect, or in many quali- 

 ties. One may tend to produce blue eyes, one brown eyes. One 

 may tend to produce vigor, the other weakness; and similarly 

 for all structures and functions. The child gets one of the two, 

 not the other; he may get either. Some of the offspring get 

 one of the two, some get the other. 



Furthermore, the different pairs of genes of the same parent 

 are in a measure independent in the way they are distributed 

 to the offspring. If the child gets the paternal gene of one 

 pair, he may get either the maternal or the paternal gene of 

 any other pair.^ Thus there is a great number of possible 

 different combinations of genes from one parent that may 

 pass to diverse children. If there were but two pairs of genes 

 there would be four diverse combinations, any one of which 

 might be received by the offspring. For four pairs the number 

 of different combinations is i6; for ten pairs it is over a 

 thousand ; for one hundred pairs the number is unimaginably 

 great (it is two to the hundredth power). Since for higher 

 organisms the number of pairs of genes is much above one 

 hundred, the number of different combinations of genes that 

 may be received by the different children from one parent is 

 very great. 



From the other parent the diverse children may receive an 

 equally great number of different combinations of genes. Any 

 combination from one parent may meet in the child any 

 combination from the other. The result is that the number 

 of different types of offspring that might be produced from 

 a single pair of parents is almost inexpressibly great. Each of 

 these types of offspring would have a different set of genes 

 and a different set of characteristics. 



Thus reproduction from two parents is a great process of 

 producing individuals with new combinations of genes and 



