The genetics of cotton

Summary

1. The inter-barbadense cross Egyptian brown × Sea Island white gaveF ₁ intermediate and complicated segregation of the blending type inF ₂. This was demonstrated to be due to the fact that the factorK ^B of the brown parent was accompanied by a number of plus modifiers absent in the white parent.

2. Repeated back-crossing of heterozygotes to the brown parent had the effect of equalising the plus modifiers of both the dominant and recessive phases of the factorK ^B. Selfing after three back-crosses gave simple segregation into 3 brown: 1 light brown.

3. A negative correlation was shown to exist between lint colour and lint length, the factorK ^B or a factor closely linked to it conditioning a shortening in the lint length of approximately 5·1 mm. in the homozygous phase and 2·7 mm. in the heterozygous phase.

4. Minor colour factors were also correlated with variations in lint length.

5. The blending type of inheritance of brown lint in Egyptian × Sea Island is considered to be due to the disintegration by human agency of an original brown-lint factor complex.

6. The cross of brownbarbadense × brownhirsutum was found to involve duplicate genes for lint colour. The distribution of the known pairs of duplicate genes inG. barbadense andG. hirsutum is discussed.