72Exhibit M 6a—7A.
M 6b
M 7aDark axil Ï f Light axil
Sterile J * t Fertile
Fi Dark axil
Fertile
Fa Dark axil Dark axil Light axil f*Light axill
Fertile Sterile Fertile [ Sterile J
Approxi- ; *■ 2 1 1
mate ratio* 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 F,; thus :—
Light I f Dark
Sterile} X [Fertile
F, Dark Fertile
F2 Dark Dark Light Light
Fertile Sterile Fertile Sterile
Ratio. 737 31 3i 225
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.Example of association of characters in heredity.
Purple flower colour is dominant to red in the sweet pea, and the
old-fashioned erect form of standard with the central notch is dominant
to the hooded. In families where these characters are involved, the
nature of the F2 generation depends upon the manner in which the
cross was made.
(A) When one dominant character goes in with each parent.
Purple) (Red
hood J (erect
Purple erect
I I I I
Purple Purple Red | *Red^
erect hood erect I hood J
Approxi- 2 , x
mate ratio . .
* Not yet found in this mating, but probably occurs very rarely.
