Canyon Crest Academy - Biology

Drosophila Lab

Canyon Crest Academy - Biology

Purpose: What is the Mode of Inheritance for my phenotypic trait?

Background: Please include information/pictures on the Drosophila life cycle, discussion of what homozygous and heterozygous means, as well as an explanation of the different modes of inheritance (autosomal recessive, autosomal dominant, etc.).

(No hypothesis!)

(Make a materials list)

Procedures:

This genetics experiment will be carried on for several weeks. Drosophila with well-defined mutant traits will be assigned to you by your teacher. You are responsible for making observations and keeping records concerning what happens as mutant traits are passed from generation to the next. Make sure you also collect qualitative data about the different flies as you go. You will cross and observe 2 generations of flies.

You will be assigned to study a certain mode of inheritance using particular genetic crosses of flies having one mutation. The modes of inheritance most commonly used are:

Monohybrid. In these experiments, the mode of inheritance is determined when a single contrasting pair of traits is involved. (can be dominant or recessive)

Sex-linked. In these experiments, the mode of inheritance is determined when the mutant characteristic is associated with the X chromosome. (can be dominant or recessive)

1.  Each group will receive 3 vials: 1 normal male and female vial, 1 mutant male and female vial, and 1 virgin (normal) female vial.

2.  Begin by practicing using the Flynap on your vial of normal males/females (not the virgins!)

Note: The goal is to expose the flies to the FlyNap for the minimum possible time. If they’re exposed for too long, they will become infertile or die.

-Gather the bottle of FlyNap, a FlyNap wand, a container to pour the flies into, the vial with flies in it, and an empty glass vial (no food, no flies).

-Go into an unused room.

-Transfer the flies to the empty glass vial. (FlyNap reacts with the plastic in the plastic vials.) Be careful not to break the glass vials!

How to transfer flies:

When flies must be moved from one food vial to another you will need to “transfer” them.

Open the fresh vial.

To keep the flies from escaping, it is good to tap them toward the bottom of the vial. You can do this by gently tapping the vial on a padded horizontal surface. A book on a desk works well.

Gently tap the flies toward the lower half of the side of the vial currently containing flies (the “used” vial).

Remove the plug from the used vial and tip the used vial upside down directly over the new vial.

Gently tap the new vial/used vial stack on the padded surface.

When the flies have transferred, turn both vials upright while continuing to tap them gently on the padded surface. (This keeps the flies from escaping.)

Plug both vials.

Flynap continued…

Bend back the top of the FlyNap wand about 1cm from tip (i.e., the non-brush end). This bend will allow you to hang the brush from the top of the vial.

Stick brush end of wand into FlyNap bottle.

Gently tap flies down to bottom of their vial. (use a book to tap on)

Remove plug from vial, pull FlyNap wand out of FlyNap bottle (dragging it along the inside of the neck of the bottle to remove excess FlyNap), quickly stick FlyNap wand into vial, and then replace plug.

WATCH CAREFULLY!

-While you are observing the flies, notice where the FlyNap wand touches the side of the vial. When you later pour the flies out of the vial, be sure to pour the flies along the opposite side of the bottle. Otherwise, they will get caught in the FlyNap drop, and they will get stuck or injured on their way out. (A good technique is to place your pointer finger over the side with the FlyNap and pour them out on the side where your thumb is.

-After 70 to 80 seconds, the flies will stop walking around and be reduced to mild twitching.

-While you are observing the flies, gently tap the vial on a padded surface

to keep the flies at the bottom of the vial. (After 20 seconds or so, you

will be able to stop the tapping, because the flies will become too groggy

to climb the walls of the vial.)

-When the last fly stops walking, immediately pour the flies into an open container such as a bowl. The flies should remain asleep for an hour or more, although some of them will continue to twitch a little bit, just like dogs sometimes twitch when they’re dreaming.

Note: If you’re going to continue to use the same vial that you anesthetized the flies in, bear in mind that there may be FlyNap on the plug or on the side of the vial. You should get a new plug if the plug is contaminated. If there is FlyNap on the side of the vial, you should wash it off and then dry the vial thoroughly.

Note: When flies get a bit too much Fly Nap, after they awaken you will notice that they will hold their wings at a 90° angle with respect to their bodies. It’s important to realize that this is not a phenotypic trait caused by a mutation, but rather the result of an environmental trauma.

3.  Take the container of flies back to a microscope.

4.  Gently place the flies onto a 3x5 card under the microscope. Be careful with the flies. They are very small and light and can be flicked off the card very easily!

5.  Using the brush, put all the flies into 1 line from left to right.

6.  Push males up and females down, thus separating the sexes.

Left: male Right: female

Young male flies have a reddish orange spot at the tip of the underside of their abdomens.

On male flies, the dorsal side of their abdomen is dark for the last 3 or so segments; on female flies, the same area is striped. (This is harder to see in Ebony flies.)

Male flies have a rounded tip end of the abdomen; female flies have a pointed tip. NOTE: IF YOU ARE UNSURE OF THE SEX, IT IS BETTER TO ERR ON THE SAFE SIDE BY PLACING THE UNCLEAR SEX BACK IN THE ORIGINAL VIAL WITH THE REST OF THE FEMALES (NOT THE VIRGIN VIAL!)

7.  Return these flies to their original vial with food and plug the top.

8.  Gently tap on the vial to get all the sleeping flies off of the food. Any who sleep on their food will drown. Lay the vial on its side until the flies all wake-up.

9.  Repeat steps 1-8, the flynapping and sexing procedure with your mutant flies.

10.  Place the mutant females back into their original vial.

11.  Place the male mutants into the vial with virgin (normal) females. Again, don’t forget to tap the vial and make sure none of the sleeping flies remain on their food. Leave the vial on its side!

12.  This is your parental generation (P). Their children, which will come out of their pupae in 2 weeks will be the F1 generation.