98 MENDELISM chap, ix 



in which all the four kinds of gametes are produced in equal num- 

 bers is, of course, that of a simple Mendelian case where no coupling 

 occurs. 



Now, as the table shows, it is possible to express the gametic series 

 by a general formula (n + i) AB + Ab + aB + (n — i)ab, where 2 n 

 is the total number of the gametes in the series. A plant produc- 

 ing such a series of gametes gives rise to a family of zygotes in 

 which 3 n 2 — (2 n — 1) show both of the dominant characters and n 2 

 — (2 11 — 1) show both of the recessive characters, while the number 

 of the two classes which each show one of the two dominants is 

 (2 n — i). When in such a series the coupling becomes closer the 

 value of n increases, but in comparison with n 2 its value becomes 

 less and less. The larger n becomes the more negligible is its value 

 relatively to n 2 . If, therefore, the coupling were very close, the series 

 3 n 2 — (2 n — 1) : (2 n — 1) : {in — 1) : n 2 — (2 n — 1) would approx- 

 imate more and more to the series 3 n 2 : ;? 2 , i.e. to a simple 3 : 1 

 ratio. Though the point is probably of more theoretical than 

 practical interest, it is not impossible that some of the cases which 

 have hitherto been regarded as following a simple 3 : 1 ratio will 

 turn out on further analysis to belong to this more complicated 

 scheme. 



