In this lab students explore the genetic consequences of gene linkage using an F1 cross of Drosophila.
172050 Two-Point Linkage:The vial of F1 flies is from a cross between females having yellow bodies and white eyes (172290 yellow white) and wild-type males having gray bodies and red eyes (172100 wild type). Yellow (y) and white (w) are recessive and are located on chromosome 1. Chromosome pair 1 consists of the sex chromosomes. The loci for yellow (linkage position 0.0 ) and white (linkage position 1.5) are on a portion of the X chromosome that has no homolog on the Y; thus, yellow and white are inherited only through the X chromosome, making them sexlinked (or X-linked). Because two sex-linked genes are used, the results of linkage can be seen in the F1. Recombinations resulting from crossovers can be seen in the F2.
The activity assumes that students have previously worked with Drosophila and know how to sex flies and perform other common tasks. If this is not the case, refer students to the pertinent sections of the Carolina Drosophila Manual. Students should also be familiar with dihybrid and sex-linked crosses.
Since Drosophila 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.
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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 apronswhen appropriate. Model proper laboratory safety practices for your students and require them to adhere to all laboratory safety rules.
Have students work individually or in pairs. Each person or pair needs an empty culture vial with plug, sorting brush, index card, Carolina™ Drosophila Manual, and access to a stereomicroscope. Provide a 172050 culture and a FlyNap® kit for every 3–4 groups.
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-hand quadrant gives information on the female flies used for the cross, and the upper right gives information on the male flies. The lower left-hand quadrant is stamped with the date that the parent flies were placed in the vial. F1 flies should begin emerging 12 to 14 days after the date on the label. Each culture will produce approximately 100 flies over a 10-day period. Cultures should not be used beyond 12 days after receipt because offspring of the F1 flies may begin to emerge.
Either prepare the fly morgues with alcohol (one morgue is included in each FlyNap® Kit) and set up culture vials with Formula 4-24 Medium or provide materials and instructions so the students can prepare the morgues and vials themselves.
Optional: In the interest of time, it is possible to stop this lab after the prediction of the expected F2 results and not set up the F2 cultures. Calculation of linkage can be performed using the supplied sample data.
| Phenotype | Males | Females |
| Gray body, red eyes | 0 | 12 |
| Yellow body, white eyes | 8 | 0 |
| y+w + | Y0 | |
| y w | y w/y+w + | y w/ Y0 |
y w/y+y + x y w/ Y0
| y w | Y0 | |
| y w | y w/ y w | y w/ Y0 |
| y+ w+ | y+ w +/ y w | y+ w+/ Y0 |
| y w | Y0 | |
| y+ w | y+ w/ y w | y+ w/ Y0 |
| y w+ | y w +/ y w | y w+/ Y0 |
| Non-recombinants | Count | Recombinants | Count | |
| yellow bodied white-eyed female | 128 | gray-bodied white-eyed female | 2 | |
| gray bodied red-eyed female | 149 | yellow-bodied red-eyed female | 1 | |
| yellow bodied white-eyed male | 131 | gray-bodied white-eyed male | 0 | |
| gray bodied red-eyed male | 140 | yellow-bodied red-eyed male | 3 |
Map distance = total recombinants/total flies counted x 100 = 6/554 x 100 = 1.1
*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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