Evolutionary genetics / edited by D.L. Jameson.

Date:
[1977], ©1977
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Evolutionary genetics / edited by D.L. Jameson. Source: Wellcome Collection.

    158/360 (page 138)
    66 THE AMERICAN NATURALIST [Vol. XLIV glumes blackness behaved as a simple Mendelian mono- hybrid, yet in one case there were two definite inde¬ pendent Mendelian unit characters, each of which was allelomorphic to its absence. Furthermore, in most varie¬ ties of oats having a ligule, the character behaved as a mono-hybrid dominant to absence of ligule, but in one case no less than four independent characters for presence of ligule, each being dominant to its absence, were found. In wheat a similar phenomenon occurred. Many crosses were made between varieties having red seeds and those having white seeds. In every case but one the gen¬ eration gave the ordinary ratio of three red to one white. In the one exception—a very old red variety from the north of Sweden—the ratio in the generation was 63 red to 1 white. The reds of the F^ generation gave in the F^ generation a very close approximation to the theo¬ retical expectation, which is 37 constant red, 8 red and white separating in the ratio of 63:1, 12 red and white separating in the ratio of 15:1, 6 red and white separating in the ratio of 3:1, and one constant white. He did not happen to obtain the expected constant white, but in the total progeny of 78 F2 plants his other results are so close to the theoretical calculation that they quite convince one that he was really dealing with three indistinguishable but independent red characters, each allelomorphic to its absence. Nor can the experimental proof of the two colors of the oat glumes be doubted. The evidence of four characters for presence of ligule in the oat is not so conclusive. In m}^ own work there is sufficient proof to show that in certain cases the endosperm of maize contains two indis¬ tinguishable, independent yellow colors, although in most yellow races only one color is present. There is also some evidence that there are three and possibly four inde¬ pendent red colors in the pericarp, and two colors in the aleurone cells. The colors in the aleurone cells when pure are easily distinguished, but when they are together they grade into each other very gradually. 138