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infer the relative position of a set of linked alleles based on recombination frequency.

Culturing We will use clear plastic vials (1.25” diameter x 4” high) with plastic foam plugs for culturing. The special culture medium developed by Carolina Biological Supply (Formula 4-24® Blue) is in flake form and you simply add equal volumes of Instant Drosophila Medium and tap water to the vials, then allow the mixture to sit for about a minute. The medium is supplied with small plastic cups for measuring media and water. After the medium has been prepared, add about 6–10 grains of dry yeast to each vial. Growing larvae will feed on the yeast, but too much yeast will kill the culture. The vials are now ready for adding flies. Virgin Females Genetics experiments require that the parents of the offspring are known. For example, if you want to determine the outcome of mating a yellow-bodied female with a wild-type male, then you must be certain that the female has not mated with any other males besides wild-type males. Because females can store sperm for weeks after a single mating, it is important to isolate females before they have had the opportunity to mate. After mature pupae are present in the culture containing the females of interest, clear all adult flies from the vial by tapping them into a clean, dry vial with a foam plug. Be sure all living adults have been removed from the vial. Vials of adults can be placed in a freezer for 15 minutes, then discarded into a special container labelled as the Fly Morgue. Any flies emerging for about 10 hours after the cultures have been cleared are virgins. You only need this method to obtain virgin females; males used in matings do not need to be virgins.