Fruit Fly Genetics Lab

Fruit Fly Genetics Lab

Setting up Your F1 Fly Crosses

Procedure

Step 1: Setting up a culture for your flies

Get a plastic vial, powdered media, water, 5 grains of yeast, and a foam plug. Take equal amounts (one small cupfull) of powdered media and water and gently mix in the bottom of the vial. Put no more than five grains of yeast onto the reconstituted media (This will help to prevent molding.).

Step 2: Getting your F1fruit flies

For this you will need a vial of male/female sex-linked or apterous (wingless) flies (you only need to do the experiment for either eye color or presence of wings, not both), and some Fly-Nap.
Transfer the swab of fly nap to the vial of flies, taking care not to let any get away. Wait until all of the flies are clearly asleep. Dump them onto a white card to examine them. Take out 5 females and 5 males that you will be breeding. Place your prepared culture horizontally and carefully brush your flies into it with your paint brush.
**Note**
In order to properly identify the flies as male or female, look at the bottom of the abdomen. Males will have dark bristles located here. If still not sure, look at the top of the abdomen. Males have a solid, dark tip, while the females appear to have a striped tip. If this is still not clear to you, get help.
**End of Note**
Put the foam rubber plug into the top of the vial. Then place your culture in a place where it can remain horizontal until the flies awaken. (This will prevent your flies from getting stuck in the media.) Make sure you have recorded your Punnett Square predictions on your fly data worksheets. (You will be keeping this worksheet to record your data from this experiment, and in order to help you write your lab report at the end of this activity.)

Step 3: Observing your culture

Now it's time for you to sit and wait for a while. Your males and females should soon mate, and produce eggs. These eggs will hatch and larvae will emerge. (These are the F2 generation.) These will probably stay in the media, until the pupae form. These will stay on top of the media, and will look kind of like rice. As soon as you see pupae, use Fly-Nap on the parents, and dispose of them in soapy water. When a considerable amount of the F2 generation flies have emerged as adults you will put them onto a white card and count them. Make sure to pay attention to the feature that you're looking for (eye color or presence of wings). Record this for your males and females. Dispose of the remaining flies in soapy water. Count newly hatched members of the F2 generation a few days later to double check your previous results. Again, dispose of the flies.

*You should count the F2generation at least a few times, taking care to dispose of the counted flies so as not to recount them. Observe the flies (after using Fly-Nap on them) counting how many display which trait (eye color or wing presence). Write this down. Organize this information in the data table on your fly data worksheet. Once you have completed all of your counting, you should be able to determine if the trait you were observing was sex-linked or not. To be on the safe side, you will be sharing your data with your classmates, and from this compiled information you will determine whether or not the trait is sex-linked.