Abstract
According to the genetico-physiological studies of the production of flower-colours in Pharbitis Nil, the coexistence of four complementary genes Ca, C, R, A is essential for the production of anthocyanin pigments in flowers. Among these genes, two genes Ca, C concern with the production of flavones from which anthocyanin is derived, gene R takes part in the function of converting flavones into anthocyanin, with the cooperation of gene A. The formation of the colour in the stem is developed by the coexistence of three genes Ca, R, A the gene C being non-related with them.
The gene A which is considered as activators of the gene R, is composed of two duplicate genes, so far as the studies have covered. However, the present studies indicate the fact that the gene A is composed of five genes denoted as A1, A2, A3, A4 and A5, and also that three, perhaps five among these genes are duplicate ones.
The function of the gene R is made active by anyone of these polymeries. In the presence of the gene Ca, every gene of these recessive genes or a1, a2, a3, a4 and a5 results in a white flower with green stem, as well as the recessive r of the gene R. Thus the white flower with green stem in this plant is numerous in genotype, though the flower-tube is either coloured or white.
Each hybrid from two crosses worked out between two white flower strain which are same in appearance, in other words same phenotype, segregates four phenotypes as its offspring, but does not always give them in the same ratio of the segregation. Crossing a green stemmed white flowered strain which has a coloured flower tube, its genotype being CaCRa, with a coloured stemmed white one, its genotype being CacRa, the hybrid results in a coloured flower which is entirely unlike to both parents. And the offspring of the hybrid gives rise to four phenotypes i. e., coloured flowers, green stemmed white ones with the coloured flower-tube, colored stemmed white ones with white flower-tube, and green stemmed white one with white flower-tube, in the normal dihybrid ratio.
On the other hand, the hybrid from a cross between a green stemmed white flower strain with coloured flower-tube of the genotype CaCrA and a coloured stemmed white one of the genotype CacRA, bears equally coloured flowers, as well as the hybrid from the cross mentioned above, while though the offspring contain four phenotypes, they do not segregate four phenotypes in the normal dihybrid ratio, but give such a segregation that shows the occurrence of a linkage. The linkage happens between c and r, the recombination value being the variation from 25.0±1.40% to 38.9±3.01%.
Then, two genes c and r are inserted into the Yellow linkage group. The linkage group into which five genes a1, a2, a3, a4 and a5 are inserted, is as follows : gene a1 which may be identical to Dr. Imai's w2a is inserted into the Duplicate linkage group, gene a2 into the Contracted one, together with gene a3 which may be identical to his w2b, gene a4 into the Variegated one, gene a5 into the Cordate one.
