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D Genetics of Drosophila and Other Insects

Most people have seen this cosmopolitan fly without recog­ nizing it. It is quite literally a commensal, for on a warm evening it will be found hovering over a wine glass, attracted by the scent of alcohol, or by any fermenting fruit which carries its food - yeasts. It is a dipteran like the blowfly or the housefly, only smaller, and it weighs about 1 mg. The smaller male has a black abdomen (hence melanogasterj and the sexes are therefore easily distinguished. The female is very fertile and can lay up to 100 eggs per day at peak, and perhaps 2000 eggs during her 60-70 day lifetime. The flies can be easily cul­ tivated on any source of yeasts. Originally it was cultivated on banana in the equivalent of half pint milk bottles (and if you place a rotting banana by your window and then keep it in a closed jar for a few days, you will almost certainly find Drosophila larvae growing there). Nowadays a maize meal - molasses mix firmed with agar which supports the tunnelling larvae for their three feeding days prior to pupation - is gener­ ally used as a standard. The egg-adult life cycle takes about 10 days at the optimum temperature of 25°C, so one can reasonably expect to grow up to 30 generations per year. It was this short operation time, minimal space requirement and low handling costs which gave Drosophila its advantage over other animals (e.g. mice) being used for genetic experiments. However, it also brought other benefits.