+-------+------------------+---------+---------------------------------+ |No. of | Distribution of | No. of | | |Gametes|Factors in Gametic| Zygotes | Form of F_2 Generation. | | in | Series |produced.| | |series.| | | | +-------+------------------+---------+---------------------------------+ | | AB. Ab. aB. ab. | | AB. Ab. aB. ab. | | 4 | 1: 1: 1: 1 | 16 | 9 3 3 1 | | 8 | 3: 1: 1: 3 | 64 | 49 7 7 9 | | 16 | 7: 1: 1: 7 | 256 | 177 15 15 49* | | 32 | 15: 1: 1: 15 | 1024 | 737 31 31 225* | | 64 | 31: 1: 1: 31 | 4096 | 3009 63 63 961 | | 128 | 63: 1: 1: 63 | 16384 | 12161 127 127 3969* | | 2n |(n-1): 1: 1:(n-1) | 4n^2 |3n^2-(2n-1) 2n-1 2n-1 n^2-(2n-1)| +-------+------------------+---------+---------------------------------+ Now, as the table shows, it is possible to express the gametic series by a general formula (n + 1) AB + Ab + aB + (n - 1) ab, where 2n is the total number of the gametes in the series. A plant producing such a series of gametes gives rise to a family of zygotes in which 3n^2 - (2n - 1) show both of the dominant characters and n^2 - (2n - 1) show both of the recessive characters, while the number of the two classes which each show one of the two dominants is (2n - 1). 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 3n^2 - (2n - 1) : (2n - 1) : (2n - 1) : n^2 - (2n - 1) would approximate more and more to the series 3n^2 : n^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. * * * * * {99} CHAPTER X SEX [Illustration: FIG. 17. _Abraxas grossulariata_, the common currant moth, and (on the right) its paler lacticolor variety.]