Fruit Fly Genetics Lab


Step 1: Setting up a culture for your flies

Get a plastic vial, powdered media, water, 5 grains of yeast, some orange screen, and a foam plug. Take equal amounts of powdered media and water and mix in the bottom of the vial. Put no more than five grains of yeast onto the reconstituted media (I forget why. If you have just got to know, ask a biology teacher.). Push the orange screen into the media until it touches the bottom of the vial.

Step 2: Getting your fruit flies

For this you will need a vial of female red-eyed or winged flies and a vial of male/female white eyed or wingless flies (you only need to do the experiment for either eye color or presence of wings, not both), a knockout vial, and some Fly-Nap.
Transfer to the knockout vial some flies from the female-only vial, taking care not to let any get away. Use the Fly-Nap on them. Dump them onto a white card and examine them to make sure that they're what you need. Take out 5 to 6 females that you will be breeding. Place your prepared culture horizontally and brush the flies with a pun brush into it. Repeat this with the flies from the male/female vial. Brush into the horizontal vial the 5 to 6 male white-eyed or wingless males you will be using.
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.

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. Thse eggs will hatch and larvae will emerge. These will probably stay in the media, until the pupae form. These will stay on top of the media, and will look kinda like Rice-Krispies. However, they are not to be taken internally. As soon as you see pupae, transfer the parent (P) generation to the knockout vial, use Fly-Nap, and dispose of them in soapy water.

Step 4: Counting the F1 generation

When a considerable amount of the pupae have hatched, transfer them to the knockout vial and use Fly-Nap. Put them onto a white card and count them. Make sure all have the same feature that you're looking for (eye color or presence of wings). Whatever feature they show will be the dominant feature. Record this. Dispose of the remaining flies in soapy water. Refer to step 1 and make a new generation in this culture. Count newly hatched members of the F1 generation a few days later to double check your previous results. Again, dispose of the flies.

Step 5: Observing and counting the F2 generation

Once you've gotten finished counting the F1 generation, it's time to wait for them to breed with each other and produce the F2 generation. Dispose of the F1 generation when you see pupae on top of the media. This time around, you are going to have to do more counting than before. You should count the F2 at least 8 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. You will be counting in all a few hundred flies, so it gets kinda hard to keep all this stuff in your head. Organize this information in a neatly-made data table. 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.

Personal Data Tables

The F1 Generation
Cnt #Number of flies countedDominant trait
The F2 Generation
Cnt #Tally of flies for each phenotypeRatio of phenotypes
1st5 female red
5 female white
7 male red
5 male white
1 Female red : 1 female white : 1.4 male red : 1 male white
2nd14 female red
7 female white
31 male red
14 male white
2 female red : 1 female white : 4.4 male red : 2 male white

Class Data Table

Eye Color
red malered femalewhite malewhite femaleother (if any)ratio of phenotypes
5099074610-1.1 red male :1.96 red female : 1 white male : 0 white female
male wingedfemale wingedmale winglessfemale winglessother (if any)ratio of phenotypes
475490158167-3.0 winged male : 3.1 winged female : 1 wingless male : 1.1 wingless female

Punnet Squares

Eye Color Autosomal

P generation - RR x WW
Phenotypes F1
Red Dom. - 1 red : 0
White Dom. - 1 White : 0

F2 Parents - RW x RW
Phenotypes F2
Red Dom. - 3 red : 1 white
White Dom. - 3 white : 1 red

Eye Color Sex Linked

P generation - XRXR x XWY
Phenotypes F1
Red Dom.
males - 1 red : 0
females - 1red : 0
White Dom.
males 1 red : 0
females - 1 white : 0

F2 parents - XRY x XRXW
Phenotypes F1
Red Dom.
males - 1 red : 1 white
females - 1 red : 0
White Dom.
males - 1 white : 1 red
females - 1 white : 1 red

Punnet Squares

Wings Autosomal

P generation - A-A- x A+A+
Phenotypes F1
wingless Dom. - 1 wingless : 0
winged Dom. - 1 winged : 0

F2 Parents - A+A- x A+A-
Phenotypes F2
wingless Dom. - 3 wingless : 1 winged
winged Dom. - 3 winged : 1 wingless

Wings Sex Linked

P generation - XA-XA- x XA+Y
Phenotypes F1
wingless Dom.
males - 1 winged : 0
females - 1 wingless : 0
winged Dom.
males - 1 winged : 0
females - 1 winged : 0

F2 parents - XA-Y x XA+XA-
Phenotypes F1
wingless Dom.
males - 1 wingless : 1 winged
females - 1 wingless : 1 winged
winged Dom.
males - 1 winged : 1 wingless
females - 1 winged : 0

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