The genetics of cotton - Part V. Reversal of dominance in the interspecific crossG. Barbadense Linn. ×G. Hirsutum Linn. and its bearing on Fisher’s theory of dominance
Crosses of Crinkled Dwarf × Sea Island exhibit complete dominance of Sea Island, but in crosses with other Peruvian types, dominance is slightly disturbed, producing inF1 normals with a slight trace of crinkling and some variation of the Crinkled class inF2.
A cross of Crinkled Dwarf × Upland gave an intermediateF1 with dominance becoming increasingly manifest in back-crosses of heterozygote to Upland.
Selfed heterozygotes from the first back-cross produced in one case a family indicating true reversal of dominance, the ratio 3 Crinkled: 1 normal being obtained. Reversal of dominance persisted in the next generation from this family.
Crosses involving Crinkled andG. sturtii gaveF1 strongly crinkled, but a heterozygous Crinkled ×G. sanguineum gaveF1 only slightly crinkled.
The bearing of the experiments on Fisher’s theory of dominance is discussed, and it is concluded that while the behaviour of Crinkled in Upland crosses is in accordance with the Fisher theory, the process by which genes modifying dominance are thought to have become homozygous in Peruvian involves the assumption that normals descended from heterozygotes have replaced the original normal population. This assumption is thought to be improbable.
Volume 100, 2021
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