Example of association of characters in heredity.
In the sweet pea the dark reddish purple axil is dominant to the light green one. Also the fertile condition of the anthers is dominant to the contabescent sterile condition. In families which involve these characters, the nature of the F_2 generation depends upon the way in which the original cross was made. (A) When each parent has one of the dominant characters.
[G] Not yet found, but probably occurs very rarely.
(B) If, however, both of the dominant characters go in with one parent, and neither with the other parent, they tend to remain associated in F2; thus:—
In such a cross the classes resembling the two original parents tend to be produced in excess, while the other two combinations are produced much more rarely. Nevertheless, the ratio of dark to light axil, and of fertile to sterile anthers, is, in each case, a simple 3:1 ratio.