354 GENERAL ZOOLOGY 



In the next generation (F 2 ) however, the characters separate 

 out according to the laws of chance and three different 

 classes of individuals are produced in the following ratios: 



1 BLACK: 2 BLACK (ALBINO): 1 ALBINO 



The first and third classes will " breed true." If an in- 

 dividual from either of these is bred with another like itself, 

 nothing but black or albino offspring will result. But the 

 "black (albino) 7 ' hybrids if bred together (F 2 , F 3 ) will 

 always separate out into three characteristic classes 1 

 pure black; 2 black (albino); 1 pure albino. 



Many pairs of dominant and recessive characters are 

 known. Among these the following may be mentioned: 

 brown and blue eyes in man; beardlessness and beard in 

 wheat; rough coat and smooth coat in guinea pigs ; normal 

 condition and peculiar waltzing condition in Japanese 

 waltzing mice. In each of the instances just mentioned 

 the dominant precedes the recessive condition. There are 

 other pairs of characters in which one does not dominate the 

 other, but there is always segregation of the characters in 

 the germ cells and chance for recombination after fertili- 

 zation. It is the segregation, or separating out of unit 

 characters, therefore, which is the important thing in 

 Mendelian inheritance. 



Bearers of Heredity. In heredity particular qualities 

 are not passed from parent to offspring but something is 

 transmitted which determines what the character of the 

 offspring shall be. A guinea-pig, for example, develops 

 from a fertilized egg and is nourished by its mother during 

 development. There is no white or black hair in the 

 egg and there is nothing in the nourishment supplied by the 

 mother that makes one or the other develop. Nevertheless 

 there is something in the egg that makes black or white hair 

 develop from the material supplied to the growing embryo. 

 Evolutionists have given up the old idea that the fertilized 

 egg contained a miniature but complete animal which simply 

 enlarged its parts during development. There is not only 



