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Published online by Cambridge University Press: 14 April 2009
A significant excess of female offspring resulted when pregnant females of the D. simulans species were left to lay their eggs on food containing quinacrine. The same result occurred in a subsequent experiment in which male parents were injected with quinacrine. This was the first time that a chemical compound showing an affinity with DNA in vitro altered the sex ratio in a consistent manner. This effect had been predicted based on the unique quinacrine fluorescent staining pattern in D. simulans, in which only the Y stains intensely in mitotic chromosomes. It seems that treatment acts on spermatids or spermatozoa causing decreased functioning of the Y-bearing ones, resulting in an excess of female offspring. Interestingly, the species D. mauritiana and D. melanogaster, although very closely related to D. simulans, do not have its staining pattern and as predicted did not respond to treatment; therefore, the important parameter appears to be related to the staining pattern of mitotic chromosomes and not to the phylogenetic relationship.