The genetics of cotton

Summary

1. Further experiments are described on the mode of inheritance of the crinkled dwarf mutant ofG. barbadense Linn. when crossed with normalG. hirsutum Linn.

2. Observations were made on the characters of crinkled when transferred by repeated back-crossing toG. hirsutum (T 9). Selfing of the heterozygotes of the fourth back-cross plants produced normal, intermediate crinkled, and extreme crinkled in a 1 : 2 : 1 ratio, and the results from selfing six back-cross heterozygotes showed that no change had taken place through further back-crossing.

3. The new type ofhirsutum crinkled was apparently slightly less vigorous and productive than the originalbarbadense mutant, though under good conditions little difference was observable.

4.Hirsutum heterozygous for the crinkled factor was shown to have a slight advantage over normal under good conditions and was not at any considerable disadvantage under bad conditions.

5. Transference of crinkled to two further types ofhirsutum revealed complete or nearly complete dominance ofhirsutum to the crinkled type.

6. The bearing of the experiments on Fisher’s theory of dominance is discussed and it is concluded that modification of the theory is necessary. Complete dominance of normal over crinkled exists in two types ofG. hirsutum although the crinkled mutant does not occur in that species. It is concluded that modifiers of dominance are of advantage to the wild type and are thus selected on their own account.