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Genetic Assimilation of an Acquired Character

C. H. Waddington
Evolution
Vol. 7, No. 2 (Jun., 1953), pp. 118-126
DOI: 10.2307/2405747
Stable URL: http://www.jstor.org/stable/2405747
Page Count: 9
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Genetic Assimilation of an Acquired Character
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Abstract

1. A wild Edinburgh strain of D. melanogaster produced no flies showing a break in the posterior crossvein when bred at 25 C., but a certain number occurred (as phenocopies) when the pupae aged 21-23 hours were subjected to 40 C. for four hours. 2. Selection was practised for and against the appearance of the phenocopy, and rapid progress occurred in both directions. After about 14 generations of selection, some flies in the upward selected strain were found to show the effect even when not exposed to the heat shock. From these, lines were built up which threw a high proportion of crossveinless individuals when kept continuously at 25 C. (and even more at 18 C.). 3. The crossveinless character, originally a typical 'acquired character,' has become incorporated into the genetic make up of the selected races. A process of 'genetic assimilation' is described by which this might be supposed to happen; it depends on the tendency of selection not merely to increase the frequency of any favorable character, but also to stabilise its development. A similar suggestion has been advanced by Schmalhausen (1947). 4. The genetic basis of the assimilated crossveinless character is polygenic. There is little evidence of any definite distinction between canalising and switch genes.

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