hat the heterozygous
plant produces a series of gametes in which the factors are coupled in this
way. The intensity of the coupling, however, varies in different cases.
Where we are dealing with another, viz. fertility (F) and the dark axil
(D), the experimental numbers accord with the view that the gametic series
is here 15 FD : 1 Fd : 1 fD : 15 fd. The coupling is in this instance more
intense. In the case of the erect standard (E) and blueness (B) the
coupling is even more intense, and the experimental evidence available at
present points to the gametic series here being 63 Eb : 1 EB : 1 eB : 63
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 {97} basis,
but in some cases it may be on the 15 : 1 : 1 : 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
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 : 1. 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 experimentally. The
first term in the series, {98} 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.

+-------+------------------+---------+---------------------------------+
|No. of | Distribution of | No. of | |
|Gametes|Factors in Gametic| Zygotes | Form of F_2 Generation. |
| in | Series |produced.|