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.

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    No. 518] VARIATION 79 ten-rowed generation, so tlie complication need not worry ns at present. The results of the generation show a definite ten¬ dency toward segregation and reproduction of the parent types. I might add that in at least two cases I have planted extracted eight-rowed ears and have immediately obtained an eight-rowed race which showed only slight departures from the type. Selection from those ears having a high number of rows has also given races like the high-rowed parent without recrossing with it. It is re¬ gretted that commercial problems were on hand at the time and no exact data were recorded. It can be stated with confidence, however, that ears like each parent are obtained in the F2 generation, from which with care races like each parent may be produced. Segregation seems to be the best interpretation of the matter. These various items may seem disconnected and unin¬ teresting, but they have been given to show the tangible basis for the following theoretical interpretation. No hard and fast conclusion is attempted, but I feel that this interpretation with possibly slight modifications will be found to aid the explanation of many cases where varia¬ tion is apparently continuous. Suppose a basal unit to be present in the gametes of all maize races, this unit to account for the production of eight rows. Let additional independent interchangeable units, each allelomorphic to its own absence, account for each additional four rows ; and let the heterozygous condi¬ tion of any unit represent only half of the homozygous condition, or two rows. Then the gametic condition of a homozygous twenty-rowed race would be 8 -f AABBCC, each letter actually representing two rows. When crossed with an eight-rowed race, the F2 generation will show ears of from eight to twenty rows, each class being represented by the number of units in the coefficients in the binomial expansion where the exponent is twice the number of characters, or in this case {a-\- Ьу. The result appears to be a blend between the characters 151