Abstract
1. The hypothesis of Fisher postulates that heterozygotes are originally intermediate, and that dominance arises through selection of the gene complex, those types of heterozygotes being preserved which react most favorably with a given recurrent mutation. 2. This view is supported by work on Drosopkila, rodents and other forms, cited by Fisher, and by the researches of Dobzhansky on the multiple effects of single genes. 3. Mutations are due (a) to changes in gene structure, which may be alterations or additions of material, and (b) to actual losses of genie substance, whether partial or complete. 4. Partial or complete loss of genie material provides no explanation of the dominant and recessive conditions. 5. Demonstrable genie losses do not, therefore, always lead to the recessive state. 6. Only in so far as loss mutations are quantitative in effect and are associated with a saturation value which is exceeded by the heterozygote can they lead to dominance. 7. All the mutations from a gene which exceed s...
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