Genetics of Drosophilia

Genetics of Drosophila

First, Drosophila is the common fruit fly. The common fruit fly is some of the best organisms to study for genetic research and experimentation. This is true for a few reasons, the first of which is the small number of chromosomes which is 4, and that we have identified the genome. This means all traits are known and we can figure out where mutations take place. The second reason is the fly’s ability to reproduce quickly. A new generation is produced every week, allowing research to proceed quickly with little time for contamination from the environment. The last reason drosophila is ideal for research is the fly’s size and manipulability, since we can easily control them combined with the previous reasons makes them ideal for research. In our experimental research we attempted to observe genetic changes in three generations of flies. We were given the second generation to observe the traits and record. Our hypothesis is if the drosophilae are allowed to interbreed, then genetic variation will occur.

Materials 1. Culture vial of wild-type Drosophila 2. Culture vial A or B or C 3. Isopropyl Alcohol 10%, 100mL 4. Camel’s hair brush 5. Thermo-anesthetizer 6. Petri dish 7. Drosophila vials & labels with medium 8. Fly morgue 9. Forceps
Procedures
Part A 1. Thermally immobilize a vial of wild-type Drosophila. Your instructor will demonstrate the proper immobilization technique. 2. Observe the flies’ traits, particularly body features that distinguish males and females, eye color, and wing size and shape. Record your observations in Table 1 in the Analysis section. If, at any time during your observations, the flies begin to become active, re-immobilize them according to your instructor’s directions.
Part B 1. Obtain a vial of a prepared Drosophila cross. 2. Record the letter written on your vial in Table 2 in the Analysis sections to help you keep track of which cross you have received. This will aid in determining expected results, as well as allow your instructor to identify any problems you may be having and to help correct them. 3. Immobilize the parental generation of your cross and observe the flies under a stereomicroscope. If, at any time during your observations, the flies begin to become active, re-immobilize them according to your instructor’s directions. 4. Separate the males from the females. Note any mutations from the wild-type phenotype, as well as whether the mutation is apparent in the male or female flies. Record your observations in Table 2. 5. Place the parental generation in the morgue. 6. Place the vial (with the parental generation removed) in a warm (28°C) place to incubate to allow the F1 generation to mature. Observe the vial occasionally and record your observations. 7. When the adult flies emerge, collect, immobilize, and examine them. Note the sex of each one, as well as the presence of any mutations. Record your observations in Table 3. Be sure every group assigned to that cross has a chance to observe and count the F1 progeny. 8. Prepare a fresh culture vial: Place approximately one tablespoon of medium in the bottom of a vial. Add an equal amount of water and let it absorb. You may want to add a piece of plastic mesh to give the flies something to crawl on, but it is not essential. Insert a foam plug in the vial. 9. Place five or more mating pairs from the F1 generation into the fresh culture vial (It is not necessary that these females be virgins). Label the vial with your name(s), date, and letter of cross. Place the culture vial in a warm place to incubate to allow the F1 generation to mature. 10. Transfer the remaining non-mating F1 flies to the morgue. 11. Leave the F1 adults in the vial for about one week to mate and lay their eggs. Once they have laid their eggs and you can see larva on the sides of the culture vial (7– 10 days), remove the adults, place them in the morgue, and wait for the F2 generation adults to emerge. 12. The F2 adults will gradually emerge from the pupae over several days. As the F2 generation flies begin to emerge as adults, immobilize and examine them. Record the number of males and females, noting any mutations which may be present. Record your findings in Table
Analysis
Table 1 | Eye Color | Wing Size and Shape | Male | 1 red | 1 normal | Female | 3 red | 3 normal |
Table 2 Phenotype | No. of Males | No. of Females | Red eye normal wing | 2 | 3 | Red eye vestigial wing | 0 | 0 | White eye normal wing | 0 | 0 | White eye vestigial wing | 0 | 0 |

Table 3 Phenotype | No. of Males | No. of Females | Red eye normal wings | 50 | 47 | “ “ | 10 | 16 | “ “ | 7 | 14 | Total | 67 | 77 |

Table 4 Phenotype | No. of Males | No. of Females | Red eyes normal wings | 24 | 16 | Red eyes vestigial wings | 0 | 1 | Brown eyes normal wings | 15 | 15 | Brown eyes vestigial wings | 1 | 0 |

Conclusion
The results of this experiment support our hypothesis that in a few generations genetic variation would occur. A mutation in the F2 generation occurred causing brown eyes instead of red.

Citation
Lab # 7 Genetics of Drosophila (College Board 2001)

Questions 1. Describe the parental cross you received; use genetic symbols.
VV x VV 2. Identify the genotype the F1 flies should exhibit. Identify the phenotype. Compare your experiment results by counting the members of the F1 generation.
VV x VV, red eye normal wing. All had this phenotype. 3. Describe the F1 cross you performed, and draw a Punnett square to show allelic combinations possible in the F2 generation.
V V VV | VV | VV | VV |

4. Identify the genotype ratio the F2 flies should exhibit. Identify the phenotype ratio. Compare your experiment results by counting the members of the F2 generation.
The F2 generation should be all the same. Mutations occurred because 44% had brown eyes and 3% had vestigial wings. So these results support genetic variation. 5. Identify the type of cross you received: monohybrid or dihybrid, autosomal or sex linked, mutations, dominant or recessive.
We started off with a monohybrid sex linked cross with red eyes being dominant. Then once we crossed again we got a dihybrid sex linked cross with a mutation causing brown eyes. 6. Using a chi-square test, determine whether or not the variation between the observed and expected number of individuals of each phenotype can adequately be explained by chance alone. Use the following formula, and apply it to the chi-square table (on the following page) to determine the confidence level that states the variation is due solely to chance. χ2 = ∑ (O–E)2/E O = observed number of offspring for the phenotypic category E = expected number of offspring for the phenotypic category χ2 = _______4.55111_______ Confidence level that variability is due entirely to chance = ___0________ %
(193-225)2/225 + (30-0)2/0 + (2-0)2/0
We did not do the experiment for questions 7-9