Genetic Study of Fruit fly (Drosophila melanogaster)

Pictures of males and females

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Drosophila Experiment

Pictures of males and females

Ventral view of a male (top) and female (bottom).

Lateral view of a male (top) and female (bottom).
Note the darker abdomen and more rounded appearance of the male. Females also tend to be larger.

Removal method
Remove all flies 8-10 hours before collecting (generally, this is done first thing in the morning). Visually inspect the surface of the food to ensure complete removal of flies. After 8-10 hours (usually before you leave work), collect all females that are present. All will be virgins. Place in a fresh culture vial and wait 2-3 days to look for larvae. Virgin females can lay eggs, but they will be sterile. Since they are photoperiod-sensitive, females, tend to eclose early in the morning. Therefore, early collections will ensure the most significant number of virgins for experimentation. However, the collection is possible later in the day.

Visual method
Being able to recognize virgin females removes the necessity of emptying culture vials on a timely basis and allows students to collect their own without the need of coming to class at odd times of the day. Note that virgin females are much larger than older females and do not have the dark coloration of mature females. In addition, in the early hours after eclosure, a dark greenish spot (the meconium, the remains of their last meal before pupating) will be visible on the underside of the abdomen.
Pictures of virgin males and females:

A newly eclosed female. This is the “wet” stage, where the fly is sticky to the touch.
The wings and body have a wet appearance.

Virgin female showing the meconium (arrow).
The meconium is a dark green area and is the remains of larval food

Comparison between a mature (top) and virgin (bottom) female. This is not long after eclosure; after 4+ hours, it becomes more difficult to tell the difference between them.
Note the meconium on the virgin female.

Comparison between a mature (top) and virgin (bottom) male. The coloration is similar to virgin females; however the genitalia is distinctly different. The meconium is also found in young virgin males as in females.
Crossing flies
Once females are deemed virgins, add males. When setting up crosses, a 3:1 ratio of virgin females to males is ideal. Generally, males will mate more efficiently if they have matured for 3 days or longer. Be sure to select robust, healthy males; the older the flies, the lower the mating efficiency. Mating occurs quickly, and the behavior is fascinating to watch but will not be addressed here. Females begin laying fertile eggs soon after mating. Refer to the life cycle chart for evidence of F1 larvae. Remove adults once it has been established that enough larvae are present (typically 7-8 days after the cross) since you may not be able to distinguish parents from the F1 generation.

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