90 GENETICS AND EUGENICS 



If the type of egg which transmits color (C) is fertihzed as 

 readily by one type of sperm as by the other, combinations 

 will result which are either CC or Cc in character. And if the 

 type of egg which transmits albinism (c) is also fertihzed as 

 readily by one kind of sperm as by the other, combinations 

 will result which are either Cc or cc in character. Puttinsr 

 together the results expected from the fertilization of both 

 types, we get 1 CC : 2 Cc : 1 cc, i. e~,.one combination of color 

 with color, two combinations of color with albinism, and one 

 combination of albinism with albinism; or three combina- 

 tions which contain color (and so will show it) to one combi- 

 nation which lacks color and so will be Vhite. This agrees 

 with the observed average result. 



The albino individual may be expected to transmit only 

 the albino character (c), never color (C), which it does not 

 possess. Experiment shows this to be true. Albino guinea- 

 pigs mated with each other .produce only albino offspring. 

 But the colored individuals are of two sorts, CC and Cc in 

 character. The CC individual is pure, so far as its breeding 

 capacity is concerned. It can form only C gametes. But 

 the Cc individuals may be expected to breed exactly like 

 the first generation hybrids, which had the same composition. 

 They will transmit color (C) in half their gametes, albinism 

 (c) in the other half. Experiment justifies these expectations 

 also. The test of individual animals may readily be made by 

 mating them one by one with albinos. The pure colored in- 

 dividuals (CC) will produce only colored offspring, since they 

 transmit color (C) in all their gametes. But the other and 

 more numerous class of colored individuals (Cc} will produce 

 offspring part of which will be colored (Cc) and the remainder 

 albino (cc). The two kinds of dominant individuals, those 

 which breed true and those which do not, we may call 

 homozygous and heterozygous, following the convenient ter- 

 minology of Bateson. A homozygous individual is one in 

 which like characters are joined together, as CC or cc; a 

 heterozygous individual is one in which unlike characters are 

 joined together, as Cc. It goes without saying that reces- 



