Bifactorial experiments in Drosophila

Summary

Through experiments to properly understand the essence of the law of segregation, to master the hybridization technique of Drosophila, and to learn to record the results of mating and to master the statistical treatment. Source: Laboratory Course in Genetics

Operation method

orthogonal and anticlockwise methods

Principle

The essence of the law of free association is that genes segregate independently and non-alleles freely combine in gametes to produce four gametes in the same proportion, so that in the second generation of the hybrid there will be four phenotypes in the ratio 9:3:3:1. Therefore, in the second generation of the hybrid, there will be four phenotypes in the ratio of 9:3:3:1. This experiment is a two-way cross between long-winged gray body and stumped wing, ebony body and gray body of Drosophila, using two pairs of relative traits, long-winged gray body and stumped wing, located on different chromosomes, in order to test the law of free association. In Drosophila, gray body (E) and ebony body (e) are one pair of relative traits, and the gene determining this pair of traits is located on chromosome III; long wing (Vg) and stumpy wing (vg) are another pair of relative traits, and the gene determining this pair of traits is located on chromosome II.

Materials and Instruments

Two strains of Drosophila melanogaster: gray-bodied winged (EEvgvg) and ebony-bodied winged (eeVgV g).
Ether Cornstarch Agar Brown sugar Yeast powder Propionic acid
Stereoscopic dissecting mirror Constant temperature incubator Balance Culture and anesthesia bottles Brushes and white porcelain plates

Move

1. Choose gray body Drosophila melanogaster as the mother, ebony body long wing as the father (backcrossing can also be, but because Drosophila melanogaster can not fly, can only crawl, it is better to use as the mother). Female flies must be selected virgin flies, can be collected in 2-3d before the experiment, female and male individuals are cultivated separately, the number of according to the needs of the number. 2.

2. Firstly, anesthetize the virgin flies with gray body and pick 5 of them and transfer them to the horizontal hybrid vials, and then anesthetize the ebony body and pick 5 males and transfer them to the above hybrid vials. After the hybrid parents have all awakened in the hybridization bottle, put the hybridization bottle upright and move it into the 25℃ incubator for culture. Label the vials with the genotypes of the parents, the mating method, the date of hybridization and the name of the experimenter.

3. After 7d, release the hybrid parents. 4.

4. 4~5d later, when the F1 adult flies start to appear, observe the F1 traits for 2~3d consecutively, or concentrate on observing after releasing the parents for 7d. 5.

5. Select 5~10 pairs of F1 male and female Drosophila, transfer them to a new culture bottle (virgin flies are not needed here), and incubate them at 25℃. 6. 7d later, release the F1 flies.

6. After 7d, release the F1 parents. 7.

7. After another 4~5d, the F2 adult flies appeared and started to observe. Counting can be done continuously for 7-8 d. The counted fruit flies should be washed out in a sink.

8. Observe and count the phenotypes and number of individuals in the F1 generation, and analyze the dominant/recessive relationship between relative traits. Observe and count the phenotypes of the F2 generation and the number of individuals of different phenotypes, paying special attention to the emergence of individuals with new trait combinations. Calculate the proportion of individuals with different phenotypes and determine the inheritance pattern of the two pairs of genes.

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