Abstract
THE allelomorphic series of mutations in Drosophila known as bar-eye and ultra-bar have been much investigated owing to their variability in the number of ommatidia present. It has been shown, for example, that increasing temperature (15° C. to 31° C.) causes a decrease in the number of facets which is of an exponential or linear order; and that this rate of decrease is more rapid in bar than in full eye, and most rapid of all in ultra-bar. Flies which are heterozygous for any of these genes are intermediate in mean facet number between the corresponding homozygous parents developed at the same temperature; but they approach more nearly to one parental condition than to the other, so that one of the conditions may be considered dominant. Near 27° C. is a critical temperature at which change of dominance takes place. Others have shown that at or near this temperature, growth and rate of development both cease to be accelerated. A rise in the frequency of crossing-over in the second chromosome has also been shown to take place at about this temperature, as well as the maximum amount of muscular contraction from a certain stimulus.
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Genetics of ‘Bar-eye’ in Drosophila. Nature 122, 422 (1928). https://doi.org/10.1038/122422a0
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DOI: https://doi.org/10.1038/122422a0