IX 



REPULSION AND COUPLING 



97 



basis, but in some cases it may be on the 15 : i : i : 15 basis. But 

 though the intensity of the coupling may vary it varies in an orderly 

 way. If A and B are the two factors concerned, the results ob- 

 tained in F 2 are explicable on the assumption that the ratio of the 

 four sorts of gametes produced is a term of the series 



sab 

 7 ab 

 $ ab, etc., etc. 



In such a series the number of gametes containing A is equal to the 

 number lacking A , and the same is true for B. Consequently the 

 number of zygotes formed containing A is three times as great as 

 the number of zygotes which do not contain A ; and similarly for 

 B. The proportion of dominants to recessives in each case is 3 : i. 

 It is only in the distribution of the characters with relation to 

 one another that these cases differ from a simple Mendelian case. 

 As the study of these series presents another feature of some 

 interest, we may consider it in a little more detail. In the accom- 

 panying table are set out the results produced by these different 

 series of gametes. The series marked by an asterisk have already 

 been demonstrated experimentally. The first term in the series, 



