XI. Experiments on inheritance in parthenogenesis

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Abstract
Johannsen’s work on inheritance within “populations” of beans, extended as it has been by subsequent workers, forms a fitting complement to the Mendelian hypothesis, and the two conceptions together have enabled our knowledge of genetics to increase by leaps and bounds. The object of the present work, which was begun some years ago and which has extended beyond the limits at first planned, was to investigate inheritance within parthenogenetic animal populations from the point of view of Johannsen’s well-known work. The terminology adopted is accordingly in agreement with that introduced by him, in spite of the fact that some objections have been raised to the use of the word genotype in Johannsen’s sense, on the grounds of its prior usage with a different meaning by systematists. Where it is necessary to express the group of individuals descended asexually (in our case parthenogenetically) from a, single ancestor, the word clone has been used, following Shull. As this author points out, the extension of Johannsen’s term pure line to include groups of individuals related in this way is not legitimate. It must be distinctly understood that a genotype, and hence the individuals forming a biotype, need not be homozygous as long as they all have the same factorial composition. In sexual reproduction such heterozygous biotypes are easily recognised on breeding, but in asexual reproduction where Mendelian segregation is not taking place, they cannot be distinguished in this way from homozygous ones.

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