Fruit Fly Cross Breeding Experiment

Introduction:

The experiment conducted used drosophila or fruit flies to test certain crosses such as a sepia female drosophila x wild male drosophila, a white female drosophila x wild male drosophila, and red/vestigial female drosophila x sepia/normal male drosophila. They are easy and inexpensive to maintain and can also be easily examined (“Drosophila melanogaster”). In addition, drosophila has the most rapid reproductive rate of any dried-fruit insect (“Fruit fly (Drosophila melanogaster)”). Furthermore, drosophila are diploid organisms which means that their chromosomes are arranged in homologous pairs and for a simple phenotypic trait, there will be two copies of the gene (one on each chromosome). Pairs of genes are called alleles and for each autosomal non sex-linked gene or trait, there are two alleles. Identical alleles in an organism signify that the organism is homozygous for that gene. In this experiment, we did a monohybrid cross, dihybrid cross, and a sex-linked cross. According the basic genetic law, in our experiment, the monohybrid cross should yield 50% red females and 50% red males in the F1 generation and 37.5% Red Females, 12.5% Sepia Females, 37.5% Red Males, and 12.5% Sepia Males in the F2 generation. The X-linked cross should yield 50% red eyed females and 50% white eyed males in the F1 generation and 25% Red Females, 25% White Females, 25% Red Males, and 25% White Males in the F2 generation.

Finally, the dihybrid cross should yield 50% red normal males and 50% red normal female in the F1 generation and 28.125% red normal males, 28.125% red normal females, 9.375% red vestigial males, 9.375% red vestigial females, 9.375% sepia normal males, 9.375% sepia normal females, 3.125% sepia vestigial males, and 3.125% sepia vestigial females in the F2 generation.

Hypotheses:

Cross I

Null: The distribution of the F1 and F2 offspring of the sepia female drosophila x wild male drosophila in cross1 will be 50% red females and 50% red males (or 100% red) in the F1 generation and 37.5% Red Females, 12.5% Sepia Females, 37.5% Red Males, and 12.5% Sepia Males (or 75% Red and 25% Sepia) in the F2 generation.

Cross 2

Null: The distribution of the F1 and F2 offspring of the white female drosophila x wild male drosophila in cross 2 will be 50% red eyed females and 50% white eyed males in the F1 generation and 25% Red Females, 25% White Females, 25% Red Males, and 25% White Males (or 50% red and 50% white) in the F2 generation.

Cross 3

Null: The distribution of the F1 and F2 offspring of the red/vestigial female drosophila x sepia/normal male drosophila in cross 3 will be 50% red normal males and 50% red normal female in the F1 generation and 28.125% red normal males, 28.125% red normal females, 9.375% red vestigial males, 9.375% red vestigial females, 9.375% sepia normal males, 9.375% sepia normal females, 3.125% sepia vestigial males, and 3.125% sepia vestigial females (or 56.25% Red Normal, 18.75% Red Vestigial, 18.75% Sepia Normal, and 6.25% Sepia Vestigial) in the F2 generation.

Methodology:

Materials- vials, fruit flies, fruit fly food, plugs, FlyNap (anesthetic), nets, microscopes, paint brushes, probes, freezer.

Procedure- To begin this lab, we must make a container that can sustain life for the fruit flies and their offspring. Since we are observing three crosses, there will be three vials needed. We added fruit fly food to each of the containers and netting inside the vials. We then added the parent generation flies needed for all three vials and sealed it with the plugs. Their traits have been checked to make sure they are the proper parent generation flies that we were supposed to observe. After we finished setting it up, we left the vials alone to let the flies breed and produce larvae which will be the F1 generation. After a few days, we placed the vials in the freezer in order to slow down to flies for removal. The parents are removed in order to prevent interference with the data The F1 flies are taken out and placed into a separate vial with FlyNap to complete incapacitate them for observation. Our group then took those flies and placed them under the microscope to see what traits they display. Between all of the crosses, we observed the sex, eye color, and in cross 3, the wing type. After counting up the flies, we removed them and left the original housing vials alone for the F2 generation to spawn. After a few days, we repeated the counting process with this generation of flies. When we finished all of the counting for our data, we released the remaining flies and cleaned out the vials at the conclusion of this lab.

Results:

Cross 1 – Sepia Female Drosophila x Wild Male Drosophila

Monohybrid Cross – Red is Autosomal Dominant

R = Red ; r = Sepia

The expected phenotype for the F1 generation of cross 1 is all red eyed drosophila, 50% red females and 50% red males

The expected phenotype ratio for the F2 generation of cross 1 is 3:1, 75% red drosophila and 25% sepia drosophila. In terms of sex, 37.5% Red Females, 12.5% Sepia Females, 37.5% Red Males, and 12.5% Sepia Males

Cross 2 – White Female x Wild Male

X – Linked Trait – White is mutant

The expected flies in the F1 generation of cross 2 are 50% red eyed females and 50% white eyed males

The expected flies in the F2 generation of cross 2 are 25% Red Females, 25% White Females, 25% Red Males, and 25% White Males

Cross 3 – Red/Vestigial Female x Sepia/Normal Male

Dihybrid Cross

The expected flies in the F1 generation of cross 3 are all red normal flies; 50% red normal males and 50% red normal female.

The expected flies in the F2 generation of cross 3 are 9 red normal flies, 3 red vestigial flies, 3 sepia normal flies, and 1 sepia vestigial fly; 28.125% red normal males, 28.125% red normal females, 9.375% red vestigial males, 9.375% red vestigial females, 9.375% sepia normal males, 9.375% sepia normal females, 3.125% sepia vestigial males, and 3.125% sepia vestigial females.

Data:

Chi-Square Test:

Discussion of Results and Conclusions:

The null hypothesis for Cross 1 was supported by F2 generations’ results. The margin of error for the chi-square in both generations is small, therefore, acceptable. However, the F1 generation was supposed to yield 100% red in fly eyes. Our results contained a few sepia flies, which ultimately leads us to reject the null hypothesis. The null hypothesis for Cross 2 is rejected for the same reasons as Cross 1. Cross 2’s F1 generation should have contained only 50% red-eyed females and 50% white-eyed males. There were flies with traits that weren’t supposed to spawn in the F1 generation (white females and red males). As for Cross 3, the null hypothesis was that there were going to be 50% red/normal males and 50% red/normal females for F1. Our results matched the expected. On top of that, the F2 results had a low margin of error as indicated by the chi-square, which means we can accept the null hypothesis.

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The F1 data for Cross 1 didn’t completely meet our expectations. There were supposed to be only red-eyed flies, regardless of sex (expected 50-50 between males and females). We ended up with a few sepia flies on the day 3 fly count. The deviation could have been set up by error. Knowing how fast flies mature and breed, one of the earlier larvae to reach adult form could have gotten enough extra time between the days to breed. Those two F1 flies could bring in F2 flies during the F1 count through sexual reproduction. It is also possible that a few of the F1 flies stayed in the vials instead of being taken out for counting. Those remaining F1 flies could have extra time to breed since they are more mature than the remain larvae and pupae. Cross 2 experienced a similar phenomenon in F1 where flies have traits they should not have. The expected results of F1 for Cross 2 should yield 50% white males and 50% red females. There should not have been any other flies with different traits than that. However like Cross 1, Cross 2’s observed results could have experienced the same scenarios of error that were mentioned earlier. Cross 3’s F1 generation experience no deviation and only yielded flies with the expected traits.

Cross 1’s F2 punnett squares estimated that the expected phenotype ratio for the F2 generation of cross 1 is 3:1, 75% red drosophila and 25% sepia drosophila. In terms of sex, that yields 37.5% Red Females, 12.5% Sepia Females, 37.5% Red Males, and 12.5% Sepia Males. The chi-square results indicate a low margin of error as the expected and observed are close without any major deviations. Cross 2’s F2 punnett squares estimated that the expected flies are 25% Red Females, 25% White Females, 25% Red Males, and 25% White Males. In terms of eye color, there were supposed to be about 50-50 whites and reds. The chi-square results of the class data show that there are were slightly more red-eyed flies spawned than white-eyed flies. The margin of error was rather significant in that case. Cross 3’s punnett squares has estimates of 28.125% red normal males, 28.125% red normal females, 9.375% red vestigial males, 9.375% red vestigial females, 9.375% sepia normal males, 9.375% sepia normal females, 3.125% sepia vestigial males, and 3.125% sepia vestigial females. Our chi square results of Cross 3 indicate precision and a low margin of error between the results and the expected percentages. Deviation in any of the crosses could have happened as a result of several scenarios. Our group did encounter difficulty extracting flies for the counting process. We tried freezing them, but given the amount of time, we had to shorten the tenure in the cold for the flies. That left some flies still active enough to accidentally escape from the lab. Even when we did manage to slow down the flies, some of them were hopelessly stuck inside the vials. Occasionally, the food paste in the vials shifted enough where it basically plasters any fly in its way. That took away several flies from our data as they could not be extracted for counting.

We seemed to be vulnerable the error in this lab and several different things could have gone wrong. As I discussed earlier, the difficulty in the removal of the flies played a major factor in skewing our data. Whether they are stuck to the paste or escaped the lab, that gives us less flies to count. Cross 2’s vial experienced the food paste shifting during our lab. A plague in our results was the appearance of flies with traits that are supposed to be absent from F1 actually appearing in our F1 data. This occurred in Cross 1 and 2. This could have been because of how fast a fruit fly matures and the amount of time given between the days we counted the flies. That could have given the F1 flies enough time to breed and spawn F2 during the days we counted for the F1 flies only. A simple issue we faced was time. The lack of time in a class period was detrimental with the incapacitation step for the counting process. We put the vials in the freezer in order to slow down the flies for transfer, but given the time, we rushed to get the counting done despite the fact that some of the flies were very active.

Works Cited

“Drosophila melanogaster.” World of Genetics. Gale, 2007. Science in Context. Web. 31 May 2015.

“Fruit fly (Drosophila melanogaster).” World of Scientific Discovery. Gale, 2007. Science in Context. Web. 31 May 2015.

Digital image. Fruit Fly Head HD Desktop Wallpaper: High Definition: Mobile. N.p., n.d. Web. 07 June 2015.

Digital image. The Conversation. N.p., n.d. Web. 7 June 2015.