CAROLINA LABSHEETS
Drosophila is one of the most popular model organisms for the study of genetics. One hindrance to using Drosophila, however, 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 only mate among themselves, so your students need only to collect F1 flies and set them up in fresh vials to produce an F2 culture. Each F1 culture can be used to set up about eight vials to produce F2 flies.
The following F1 autosomal crosses are available. The phenotypes used for these crosses are easily distinguishable from the wild type. They are also widely used in lab manuals and textbooks. Since the crosses must be set up before shipment, please give a 2-week notice for delivery of the cultures. Otherwise, the crosses may not be available when you need them. We can also do custom F1 crosses (172055). Select the parents from our general listing of Drosophila strains and notify us 6 weeks before the desired delivery date.
A vial of F1 flies from a cross between wingless (172320 apterous) and winged (172100 wild type) parents. Apterous (ap) is recessive and is located on chromosome 2. The expected F2 ratio is 3 wild type: 1 apterous.
A vial of F1 flies from a cross between dark brown-eyed (172575 sepia) and red-eyed (172100 wild type) parents. Sepia (se) is recessive and is located on chromosome 3. The expected F2 ratio is 3 wild type: 1 sepia.
A vial of F1flies from a cross between wingless(172320 apterous) and dark brown-eyed (172575 sepia) parents. Apterous (ap) is recessive and is located on chromosome 2. Sepia (se) is recessive and is located on chromosome 3. Apterous flies are wild type for eye color, and the sepia flies are wild type for wings. The expected F2 ratio is 9 normal wings, red eyes: 3 normal wings, sepia eyes: 3 apterous, red eyes: 1 apterous, sepia eyes.
A vial of F1 flies from a cross between reduced wings (172460 vestigial) and dark brown-eyed (172575 sepia) parents. Vestigial (vg) is recessive and is located on chromosome 2. Sepia (se) is recessive and is located on chromosome 3. Vestigial flies are wild type for eye color, and the sepia flies are wild type for wings. The expected F2 ratio is 9 normal wings, red eyes: 3 normal wings, sepia eyes: 3 vestigial, red eyes: 1 vestigial, sepia eyes.
A vial of F1 flies from a cross between reduced wings (172460 vestigial) and dark-bodied (172500 ebony) parents. Vestigial (vg) is recessive and is located on chromosome 2. Ebony (e) is recessive and is located on chromosome 3. Vestigial flies are wild type (tan) for body color, and the ebony flies are wild type for wings. The expected F2 ratio is 9 normal wings, normal body color: 3 normal wings, dark body: 3 vestigial, normal body color: 1 vestigial, dark body.
For sex-linkage, see our Genetics with Drosophila F1 Crosses: Sex-Linkage Labsheet.
Our Drosophila F1 cultures make it easy to study crosses because we deliver exactly what you need.
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 medium 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. Add a level cup of medium to each vial. When all the vials have dry medium, add a level cup of cool water to each vial. Open the yeast packet and sprinkle a few (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.
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 medium and possibly becoming stuck. At the beginning of the lab, students will pick up the flies on index cards.
Students will also need the following materials for doing initial observations and setting up cultures for F2 flies:
Since the students do not have to select female flies of one strain to mate with males of another, the lab does not ask them to practice sexing the flies. If you would like students to practice sexing of flies, refer to page 12 of the Carolina Drosophila Manual and have them do that as part of the Observing activity.
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:
F2 flies will begin emerging about 12–14 days after students have set up their vials. Begin scoring phenotypes of the F2 on the day after the flies 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; they 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:
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. The activity can be made more investigative by removing the label from the F1 culture vial and asking the students to analyze the cross without the information provided on the vial. For a demonstration of the use of FlyNap®, students can watch our Observing Phenotypes with Drosophila melanogaster video. (See above).
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.
Note the eye color and wing type of your F1 flies here. Note: if you are using the 172035 F1 vestigial x ebony, change “eye color” to “body color” for the phenotype.
Eye color wild type
Wing type wild type
F2 Phenotypes and Numbers of Flies
| Date Counted | Phenotype 1 | Phenotype 2 | Phenotype 3 | Phenotype 4 |
|---|---|---|---|---|
| Total | 362 | 133 | ||
| Expected Ratio | 3 | 1 |
F2 Phenotypes and Numbers of Flies
| Date Counted | Phenotype 1 | Phenotype 2 | Phenotype 3 | Phenotype 4 |
|---|---|---|---|---|
| Total | 579 | 206 | 178 | 61 |
| Expected Ratio | 9 | 3 | 3 | 1 |
*Next Generation Science Standards® is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.
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