ix REPULSION AND COUPLING 89 



the dark axil (D] the experimental numbers accord with 

 the view that the gametic series is here 1 5 FD : i Fd : 

 i fD : 1 5 fd. The coupling is in this instance more 

 intense. In the case of the erect standard (E) and blue- 

 ness (} the coupling is even more intense, and the 

 experimental evidence available at present points to the 

 gametic series here being 63 EB : i Eb : i eB 163 eb. There 

 is evidence also for supposing that the intensity of the 

 coupling may vary in different families for the same pair of 

 factors. The coupling between blue and long pollen is 

 generally on the 7:1:1:7 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 obtained 

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

 four sorts of gametes produced is a term of the series 



3 AB + Ab + aB + 3 ab 

 7 AB + Ab + aB + 7 ab 

 15 AB + Ab + aB+ 15 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 form-ed contain- 

 ing 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 accompanying table are set out the results produced 

 by these different series of gametes. The series marked 

 by an asterisk have already been demonstrated experi- 

 mentally. The first term in the series, in which all the four 

 kinds of gametes are produced in equal numbers, is, of 

 course, that of a simple Mendelian case where no coupling 

 occurs. 



