Genetic research. A biologist holds a milk bottle in which normal & mutant fruit flies of the species Drosophila melanogaster are raised. The number of mutants tells the researcher how the genes of the parent flies have interacted. Drosophila flies have been used in genetics for many years because they multiply rapidly. The milk bottles are sterilised in an autoclave, then partly filled with a nutritious growth medium & a filter paper. The fly larvae eat the pale brown medium & pupate on the paper. When they are to be examined, the biologist knocks them unconscious with ether, from which they recover in about 10 minutes.