Laboratory 1 – Mendelian Genetics – Introduction to Drosophila and Genetic
basis of the Principle of Segregation in F2 progeny of a monohybrid cross.
In this lab we will become familiar with the fruit fly Drosophila melanogaster that is
used for conducting various genetic crosses in the laboratory. We will examine some of the
morphological features of Drosophila that show variation and set up a monohybrid cross to show
Mendel’s principal of segregation. We will also set up a cross involving a sex-linked trait.
Because the Drosophila experiment will take 10 days per generation.
Introduction to Drosophila
We will practice handling and examining Drosophila fruit flies. We will follow the
procedures from Mertens and Hammersmith – Investigation 1, with some important
modifications. We will use the Carolina Formula 4-24 Instant Drosophila Medium. We will
anesthetize flies by cooling 2 (to 2.5) minutes in freezer (no longer or else they die or become
sterile) in a vial without food and keep them cool on ice packs rather than using a chemical
anesthetic such as ether. Flies are cultured at 20-25°C in the incubators provided (these are preset
at the required temperature and require no adjustment).
Techniques for handling Drosophila
Anesthetization of flies:
Flies must be anesthetized in order to keep them inactive during examination or while
they are being transferred into culture vials for mating. You have been provided with plastic
dishes with ice, plastic containers for ice water baths, plastic petri dishes and white filter paper.
Use the following procedure to anesthetize the flies:
1. Obtain a plastic dish with ice and place a petri dish with one piece of filter paper in it on the
ice surface.
2. Shake the flies down into the bottom of the culture vial by tapping the vial, then remove the
plug and quickly transfer the flies into an empty vial.
3. Insert the vial with the transferred flies into the freezer.
4. When the flies in the vial have stopped moving about 2 minutes (check them every 15 sec
after 2 minutes), and then pour a few of them out onto the filter paper in the petri dish.
2
Do not leave flies in a freezer for more than a 2.5 minutes because they may die or become
sterile!!!
5. Flies will normally remain anesthetized if kept on an ice bath or block.
Culture vial preparation:
1. Obtain clean culture vial and foam plug.
2. Add 1 small scoop of dry food to vial.
3. Add 1 small scoop of tap water to vial.
4. Add two or three (2 or 3) grains of dry yeast to the vial.
5. Dry off any water on inside exposed walls of vial with a Kim-wipe.
6. Place foam plug in the vial to keep wandering Drosophila out.
Setting up cultures:
1. Anesthetize flies.
2. Transfer flies to an empty vial with brush.
3. After the flies wake up they can then be added to the food vials.
4. Label vial with date and types of male and female flies used.
5. Subculture the mutant and wild stocks every one to two weeks; never keep the vials with
cultures longer than 3 weeks.
Setting up reciprocal crosses:
1. Clear adults from vials once pupal cases form. (Subculture if needed)
2. Collect virgin females within six to seven hours of clearing vials.
3. Place virgin females in vial with food. (Up to 8 per vial, based on availability)
4. Add males of other stock; try to wait before adding males so the females will be strong; use
slightly less males than females.
5. Label vials properly. Two vials for each reciprocal cross are recommended.
6. Clear adults when pupal cases appear. (Set up in another vial if desired.)
7. Wait for F1 to emerge and score.
8. Collect data on the first 100 Fl’s flies to emerge from each reciprocal cross.
9. Tabulate information on the Fl generation flies with regard to sex and phenotype for each
reciprocal cross.
10. If conducting testcrosses, then F1 virgin females need to be collected.
11. When setting up the F1 flies for the F2 generation set up a new labelled vial then add an equal
number of F1 males and females. The female flies do not need to be virgins, because it does not
matter if mating occurred before or after the flies are put into the new vials as this is a sibmating.
12. Once again, clear the adults when the pupal cases appear.
13. Collect data on the first 100 F2 generation flies to emerge from each reciprocal cross.
(14) Tabulate information on the F2 generation flies with regard to sex and phenotype for each
reciprocal cross.
Keep records of your crosses in Table 1.2 on (page 9-new book) (page 8 old book), or you can
set up the information for in a MS Word file. Keep your records on the methods and data for
your crosses for the F1 and F2 generation to write up later on.
Fly Lab report is worth a 100 points. It should be made into a word document which you will need to upload to a Turn-it in link on Canvas. The link only takes one document, so make sure everything you need to include in the report is one single document.
We are using ether not freeze！！！
We are using ether not freeze！！！
We are using ether not freeze！！！
0 comments