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Drosophila is widely used model organism for the study of genetics; however, one hindrance to using Drosophila is the need to select virgin female flies for crosses. The use of our Drosophila F1 Crosses removes this obstacle. Our technicians select virgin female flies and set up the crosses to produce the F1 cultures that we ship. The F1 flies that emerge in these cultures can mate only among themselves, so your students need only to collect F1 flies and set them up in fresh vials to produce an F2. Each F1 culture can be used to set up about 8 vials to produce F2 flies.
A vial of F1 flies from a cross between white-eyed (172220 white) females and red-eyed (172100 wild type) males. White (w) is recessive and is located on chromosome 1. Chromosome pair 1 consists of the sex chromosomes. The locus for white is on a position on the X chromosome that has no homolog on the Y; thus, white is inherited only through the X chromosome, making white a sex-linked (or X-linked) gene.
Since the crosses must be set up before shipment, please give 2-week notice for delivery of the cultures; otherwise, the crosses may not be available when you need them.
empty culture vials and plugs (173076)
Formula 4-24® Instant Drosophila Medium (173200)
Drosophila sorting brushes (173094)
index cards to use as sorting trays
Carolina™ Drosophila Manual (452620)
Carolina Drosophila Stand (173030)
Our 173050 Drosophila Culture Kit includes 36 vials and plugs, labels, FlyNap® Kit, Formula 4-24®, sorting brushes, sorting cards, and a Carolina™ Drosophila Manual.
Ensure that students understand and adhere to safe laboratory practices when performing any activity in the classroom or lab. Demonstrate the protocol for correctly using the instruments and materials necessary to complete the activities, and emphasize the importance of proper usage. Use personal protective equipment such as safety glasses or goggles, gloves, and aprons when appropriate. Model proper laboratory safety practices for your students and require them to adhere to all laboratory safety rules.
Students can work individually or in groups of 2–4.
When your cultures arrive, open the package immediately and inspect the cultures to verify that they have arrived in good condition. Examine the label on each vial. The label is divided into four parts. The upper left quadrant gives information on the female flies used for the cross, and the upper right quadrant gives information on the male flies. The lower left quadrant is stamped with the date that the parent flies were placed in the vial. F1 flies should begin emerging 12–14 days after the date on the label.
Each culture will produce approximately 100 flies over a 10-day period and will serve 6–8 groups.
Either prepare a vial with media for each student group or provide materials and instructions to the students so they can prepare their own vials. Materials needed are culture vials with plugs and Formula 4-24® Instant Drosophila Medium. Open the bag of medium and locate the small measuring cup and packet of yeast. Using the small cup, add a level cup of medium to each vial. When all the vials have dry medium, follow with a level cup of cool water. Open the yeast packet and sprinkle 6–8 grains of yeast onto the surface of the medium in each vial. Do not add too much yeast. The yeast produces CO2, which in large amounts can cause sterility or even death of the flies.
Either prepare the fly morgues with alcohol (one morgue is included in each FlyNap® Kit) or provide materials and instructions so the students can do this themselves.
Observing F1 Flies and Setting Up F2 Cultures
Anesthetize flies before the lab and dump them onto sheets of paper. When the FlyNap® wand has been inserted into a vial, either place the vial upside down on a Carolina Drosophila Stand or lay the vial on its side to prevent the flies from dropping onto the media and possibly becoming stuck. At the beginning of the lab students pick up flies on index cards.
Students will also need the following materials for doing initial observations and setting up cultures for F2 flies:
vial with medium and plug
vial Label
FlyNap® Kit (if flies are to be anesthetized by students during lab)
sorting brush
index card
stereomicroscope
Clearing F1 Parents from the F2 Vials
Seven to 10 days after the F2 vials are set up, the F1 flies need to be removed from the F2 cultures. This is done to avoid including the F1 flies in the F2 counts.
The following materials are needed:
FlyNap® Kit (for every 6–8 groups of students)
sorting brush
index card
stereomicroscope
Scoring Phenotypes
F2 flies will begin emerging about 12 to 14 days after students have set up their vials. Begin scoring phenotypes of the F2 on the day after they first begin emerging. More females than males emerge on the first day, but the ratio evens out on successive days. Scored flies should not be returned to the vial but must be disposed of in a morgue to prevent them from being counted twice. Phenotypes can be scored every other day for up to 10 days. Counts carried beyond 10 days risk including flies of the next generation.
For scoring the phenotypes of the F2 flies, students will need their F2 vials and the following materials:
FlyNap® Kit (one for every 6–8 groups of students)
sorting brush
index card
stereomicroscope
As an option, you can provide cultures of the parent flies of the cross. Students can compare the phenotypes of the parental flies to the F1 culture to see which is dominant.
For a demonstration of the use of FlyNap®, students can watch our Observing Phenotypes with Drosophila melanogaster video.
Chi-square analysis is not included as part of the activity, but it can easily be added. There are several Internet sites that will perform the calculation from input data.
Red Eyes | White Eyes | |
Female | 6 | 0 |
Male | 0 | 6 |
Numbers will vary, but students should find that all the females have red eyes and all of the males have white eyes.
Table 2: F2 Phenotypes and Numbers of Flies
Date Counted | Phenotype 1 | Phenotype 2 | Phenotype 3 | Phenotype 4 |
Total | 56 | 47 | 59 | 58 |
Numbers will vary but the totals should suggest a 1:1:1:1 ratio.
Parental Cross | Xw / Xw | x | Xw+ / Y |
Female Parent | Male Parent |
F1 (give genotype and phenotype) | Xw / Xw+ (female, red eyes) , | Xw F / Y (male, white eyes) |
Cross of F1 to produce F2 (give genotype) | Xw / Xw+ | x | Xw / Y |
Female Parent | Male Parent |
Draw Punnett square Here