- Lab 9
If your knowledge of Genetics is minimal you may want to take a look at the Genetics info in BIO 113 before beginning the Virtual Fly Lab.

Drosophila Background: The common fruit fly, Drosophila melanogaster

Life Cycle: There are four distinct stages in the lifecycle of the fruit fly: egg, larva, pupa, and adult. At 25 C a fresh culture of Drosophila will produce new adults in 9-10 days

Drosophila melonogaster, your average fruit fly, is usually plain in color, with large, red eyes and oval-shaped wings. Drosophila is the premiere organism for understanding genetics and genetic mutations due to the large number of mutant strains available. Mutations in the species include changes in eye color, eye shape, body color, and wing shape.

In this laboratory, you will concentrate on mating flies using one or two of the wing shape mutations available, some of which are described below. As we said, wild-type flies are "normal" flies. They have red, oval-shaped eyes, fully-formed, smooth wings, and brownish-yellow bodies. See if you can recognize the difference in wing shape between the wild-type and mutant strains in the image. A few other types of mutations are also described (mutation names in italics).

Some of the mutant phenotypes:

Body Color: Ebony flies are reddish-brown in body color and black flies are black.

Wings: Vestigial winged flies have wings which appear tattered and uneven in contrast to those of wild-type flies. One danger in working with vestigial-winged and apterous flies is that, because of the defects in wing structure, the mutant flies do not fly as well as they should and often drown in the media.

Eyes: Bar-eyed flies have, in the homozygous condition, rod-shaped red eyes, while other flies may have white eyes, which lack pigment entirely.

Your job in this experiment will be to count the progeny which display different phenotypes, and determine the genotypes of the parents based on those of their children and their phenotypes.

Life Cycle: The flies spend five days in the egg and larval stages and four days in the pupal stage. The adult flies may live for several weeks. Drosophila cultures should not be exposed to high temperatures (e.g.. above 30 C) which result in sterilization or death of the flies or to low temperatures (e.g. below 10 C) which result in a prolonged life cycle (perhaps 57 days) and reduced viability.

Drosophila Melanogaster in a lab culture. Move your mouse over the vial to examine the stages of its Life Cycle.

The adult Drosophila female starts to deposit eggs on the second day after emergence. Embryonic development of the egg takes about one day at 25 C. The larva is white, segmented and worm like. The larval stage is a feeding stage and consists of three subdivisions called instars. The first and second instars stages end in molting which allows the larva to grow. The third instar ends with pupation. Prior to pupation, the animal stops feeding and crawls to some relatively dry surface and the cuticle hardens and darkens to form the puparium (like a cocoon). Metamorphosis occurs in the puparium and takes about four days. The pupa begins to darken just prior to the emergence of the adult fly. Most flies eclose (emerge) from the pupa in the early morning hours.

Sexing Flies - It is essential that you learn to distinguish the males from the females. With practice this becomes relatively easy and you will probably be able to sex the flies without magnification. At first it will be best to use the dissecting scopes. There are several ways of distinguishing the males from the females. I think the most reliable way is to look for the sex comb on the front legs of the male. They do not appear on the front legs of the female. This characteristic is present even in the pupa.

Click each fly from detailed information

In older flies the posterior part of the abdomen is quite dark in males and considerably lighter in females. The tip of the abdomen in more rounded in males than in females. In general the male is smaller than the female. Use a camel hair brush for moving flies around. It is easy to damage the flies if you use pencils or other objects.

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