HEREDITY. 



75 



total heritage ; the four grandparents, one quarter ; the 

 eight great-grandparents, one eighth, and so on." 



Another generalisation of great interest is Mendel's Law, 

 which seems to apply to certain cases, e.g. peas, stocks, 

 mice and rabbits. In its simplest expression the law may 

 be stated as follows. If A be a well-established variety 

 with a certain character, e.g. stature or colour, and B be 

 another well-established variety in which the same character 

 is markedly different, and if A and B are crossed, the 

 hybrid offspring (H] will usually resemble one of the 

 parents in the particular distinguishing character. The 

 character which finds expression is called the dominant; 

 the character which remains latent in the hybrids is called 

 the recessive. Now, if the hybrids are bred together, their 

 descendants will be of two kinds, some like the dominant 

 grandparent, some like the recessive parent. When those 

 like the recessive parent are in-bred, they yield only 

 recessives. When those like the dominant parent are in- 

 bred, some yield pure dominants only, that is forms which 

 if in-bred yield only dominants, but others yield apparent 

 dominants like the original hybrid, that is with the power 

 of throwing off when in-bred more pure dominants, more 

 pure recessives, and more apparent dominants like the 

 original hybrid. The results tend to be always in the 

 proportion iA + 2 A (B)+ iB. 



Two diagrams (after T. H. Morgan and R. C. Punnett) 

 may make the matter clearer. 



A 



B 



A (B) 



A 



i A 2 A (B) I B 



B 



B 



B 



