Selection of the Genetic Basis for an Acquired Character

Abstract

IN a letter under this title, Prof. C. H. Waddington¹ has described an interesting selection experiment with a Drosophila phenocopy of ‘crossveinless’. He has demonstrated clearly that the phenocopic effect, at any rate in this case, depends on individual genetic constitution as well as on the shock treatment applied to the pupæ—a fact realized by Goldschmidt² for phenocopies in general, but not followed up as Prof. Waddington has done. Analogous results have been obtained in this laboratory using the mutant ‘antennaless’³. Stocks homozygous for this gene show variable penetrance and expressivity on ordinary culture media. Selection and/or close inbreeding of individuals from such stocks can give rise to lines showing the whole range from almost zero to almost complete penetrance, representing the effects of the ‘antennaless’ gene when combined with different gene backgrounds⁴. The main difference between the two experiments seems to lie in the fact that in the crossveinless experiments the life-history includes a period of highly abnormal conditions, whereas in ‘antennaless’ the cycle is completed under normal culture conditions. The difference is, however, only one of degree, and the two situations would seem to be essentially parallel.