The phenocopies produced by feeding sodium metaborate, sodium fluoride, mercuric chloride, silver nitrate, potassium thiocyanate and semicarbazide hydrochloride toDrosophila larvae are shown to be the same as, or similar to, those described by Rapoport (1947). At suitable concentrations of the salts, 100% phenocopies can be produced in live-yeast cultures; three of the salts produce no morphoses in sterile cultures.
The primary effect of feeding sodium metaborate is the production of a phenocopy ofeyeless, but individuals copyingrough, Lobe, antennaless andarislopedia arc also found and, occasionally, the first pair of legs is modified by the treatment.
An Ore K pure line, a line derived from this(@#@ eyK@#@) but carrying an allele of ey2,and their, heterozygote, showed no response to treatment with metaborate in sterile cultures untill a threshold concentration was exceeded. This threshold was nearly the same for both lines carrying eyK, but it was considerably higher for the wild type. The presence of the eyk gane allows a smaller amount of boron to have effect than would otherwise be possible. Beyond these minimum concentrations the response curves appear to follow Parallel courses. The treatment delays larval development and increases pupal mortality, and it does so to a different degree for the three genotypes, the heterozygote being least affectted in these respects.
Sodium metaborate is found to act between the 45th and 78th hours of larval life under our conditions, and this appears to be true for the three genotypes studied. The T.E.P. for eyK hand, begins at about 30 hr. and continues to 80 hr. or so. After 80 hr. the effect of temperature on eye size is reversed. In so far as the t.e.p. can be taken as indicating the time of action of theey gene, it is clear that sodium metaborate acts in a different fashion fromeyK.
These results are discussed with respect to the known development of the eye, and it is suggested that boron acts only during the second of two or three distinct processes which regulate eye size. There is no evidence that this action involves the complete inhibition of a definite step in chemical synthesis, and hence Goldschmidt’s (1945) thesis that chemically induced phenocopies may provide evidence for the view that gene action can be divided into qualitative as well as quantitative categories, finds no support from the data. The authors wish to express their thanks to Prof. G. H. Waddington, F.R.S., who suggested this problem, and for his help with the work, and alsoto Mr D. Roberts who New PL 11.
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