By the present linkage studies, a gene a
5 for white flower with green stem was found, which has such an activity that its dominant gene produces colours in the corolla, as well as the known similar genes, A
1 and A
2, cooperating respectively with a gene R. The linkage studies were as follows: that is, a
5; links to each one of crêpe (c
p) for crêpy leaf and cordate (c
o) for cordate leaf of the cordate linkage group, the recombination frequency between a
5 and the former being 37.6 percent, between a
5 and the latter being 49.5 percent. And also a
5 links to variegeted-2 (v
2) of the same group, the recombination frequency being 44.3 percent.
In addition to the known genes, dusky (d
y) and duskish (d
k), with which the dull coloured flower is concerned, a new gene dun (d
u) was found by the studies of a cross between a normal coloured flower and a white segregated from dull coloured flower. F
1 plants from the cross was triply heterozygous in relation to genes, d
y, d
u and a
5, and there occurred coupling which has the recombination frequency of about 25 percent between a
5 and d
u. Therefore, a segregation as if it shows repulsion between white flower and dull one, was given in F
2.
Thus, two genes, a
5 and d
u came to belong to the cordate linkage group.
According to the writer's opinion, it is possible to say that the coexistence of the dominant genes as, C
a, C, R, A, D
y, D
k and D
u, is at least essential to the development of the normal pure colour in the corolla, and also among these gens C
a, C are supposed to concern with the production of chromogen, R, A with enzymes which have the rôle to formate anthocyanin pigments from chromogen, thus giving rise to the normal pure colour of flowers. The dominant genes, D
y, D
k and D
u are complementary to each other for the manifestation of the normal pure coloured flower, having the activity to make the action of the genes, R, A develop fully.
The writer intended to try the following supposition as to the activity of these dominant genes, D
y, D
k and D
u. Probably these genes refer to pH which is responsible for the activity of the genes, R, A. Therefore, in the absence of these genes, the activity of the genes, R, A is too weak to formate abundantly anthocyanin pigments from the chromogen. Thus, the mixture of the some produced anthocyanin pigments with the unreacted chromogen results in the dull coloured.
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