|
|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.]

In their simplest expression the phenomena exhibited by Mendelian
characters are sharp and clean cut. Clean cut and sharp also are the
phenomena of sex. It was natural, therefore, that a comparison should have
been early instituted between these two sets of phenomena. As a g