Introduction
The final project for our genetics studies was to breed fruit flies. We used friut flies because they have a shorter maturation period than other species and we can breed several generations within a few weeks. With this we got first hand experience with real life genetics. We chose which kind of Carolina Drosophilia we were going to cross and what characteristics we were looking for. We chose to cross white eye (w) and wild (+). The white eye flies have a white eye phenotype, and the wild flies have red eyes. Phenotypes are the physical expression of a genotype, or the way something looks. Genotypes is the genetic code for one or more specific trait/s In vial 1 we had wild females (+) and white eyed males (w). In vial 2 we had wild males (+) and white eyed females (w).
Classification
- Kingdom Animalia
- Phylum Arthropoda
- They have compound eyes, segmented antennae, and/or legs, and an exoskeleton.
- Class Insecta
- Segmented body, jointed appendages, and exoskeleton. The adults have one or two pairs of wings and antennae.
- Order Diptera
- One pair of wings, sucking mouthparts, carry diseases, destroy crops, and act as decomposers.
Phenotypes
Throughout our experiment we were using two different types of flies; wild types and white eye.
The wild type of fly has no mutations, red eyes and normal wings. Whereas the white eye flies have white eyes that are lighter than their body color so they stand out.
Group Life cycle Observations
2/27/06 flies expanded to new cultures
3/2/06 no larvae; medium dry; added water to medium
3/3/06 larva burrowing; larvae are mostly small, some medium sized
3/6/06 brown larva on vial sides; many pupa with the larva. the pupas are identical in size to larva, but are motionless.
3/8/06 lots of large larvae. pupas all over the sides. some pupa have eyes that are visible and look ready to hatch.
3/10/06 several pupa ready to hatch; P1 cross initiated
3/17/06 no larvae or pupa evidently yet
3/23/06 vials with (+) male still has no larvae. medium looks dry even after water was added. vial with (+) fem. has pupa all over the sides at least 80-90. I think that vial with the (w) fem. and (+) males has only males in it.
3/27/06 flies have hatched in vial with wild fem. red eye and white eye. vial 2 still has no flies or larvae medium shiney, looks contaminated.
3/28/06 adult flies have suddenly become present in the (w) vial. there are many flies of both phenotypes.
3/30/06 more flies in the female 2 vial (w). medium shines and peach colored. little blue spots. and lots of new larvae
3/31/06 F1 generations put in new vials for F2 vial 1 - 2 (+) red eye fem. 3 white eye males (w) vial 2 6 (+) males 6(+) fem.
4/3/06 medium has no evidence of larvae
4/6/06 F1 wild vial is uncontaminated no larvae; the other vial has numerous larvae that are becoming pupa.
4/7/06 vial 1 continues to have numerous larvae and pupa. vial 2 continues to have observable pupa.
4/21/06 flies have hatched; some pupa. Sexing The Flies
To begin with, the original fly population we possessed was anesthetized using the FlyNap kit.
After anesthesia was induced, the flies were emptied onto an index card. Referring to the characteristics of different Drosophilla sexes and phenotypes, 6 male wild-type(,) flies and 6 female white-eyed(W) mutants were identified and isolated from the rest of the fly population. This phenotype combination was reciprocated into another group of flies. After this sexing was complete the two groups were each placed in separate vials complete with a new medium. The anesthetized flies not isolated into either group were later exterminated. (In a humane way of course.)
The sexual characteristics of both mutant(W) flies and wild-type(,) flies are basically identical, depending on sex, of course. The male Drosophilla abdomen and posterior is relatively slender and appears dark because black hairs surrounding the genital region. Female Drosophilla have a wider more obtuse abdomen, and also have a relatively light posterior. The simplest way to differentiate between fly sexes is the width and the color of the flies underside.
Refer to drawing for sexual characteristics:
© 2006 twoblue2
Predictions and Outcomes
F1 Predictions
For our first generation (F1) of flies we chose to cross wild (+) males and white-eye (w) females in vial 1. In vial 2 we had (+) females and (w) males. We predicted that the mutation would be sex linked recessive. So if the female was the sex with the mutation then all females would be wild type heterozygous. Heterozygous is a term used when the two genes for a trait are opposite. the males would all be white eye since they only have one X chromosome. If the males were the sex that had the mutation then all the flies would be wild type but the females would be heterozygous.
F1 Outcomes
In vial one we crossed white eye females with wild males. And our outcomes were white eye males and wild females. In vial two we crossed white eye males with wild females, our results were we got both phenotypes in the males as well as the females.
F2 Predictions
Based upon observation of the F1 generation, we hypothesize that the inheritance of the white-eye(W) mutation is sex-linked and recessive.
Vial 1 for the F2 generation will facilitate a cross between Male(W) and Female(+). Considering the hypothesis, the prediction for the outcome of this vial is as follows: Male(+) 25%, Female(+) 25%, Male(W) 25%, and Female(W) 25%. All female(+) flies will be heterozygous.
Vial 2 will contain a cross between Male(+) and Female(+). The predicted phenotypes are: Male(+) 25%, Female(+) 50%, and Male(W) 25%. In this case all female will be homozygous.
Final Count
| Total fly counts from vial 1 | Total Female + 90 | Total Male + 86 | Total Female w 80 | Total Male w 89 |
| Total fly counts from vial 2 | Total Female + 98 | Total Male + 123 | Total Female w 0 | Total Male w 8 |
Error Analysis
F2 Vial 1 (Male-W)(Female+)
+Male: Observed-89 Expected-91; Error%- 2.2
+Female: Observed-92 Expected-91; Error%-1.1
WMale: Observed-90 Expected-91; Error%-1.1
WFemale: Observed- 92 Expected-91; Error%-1.1
F2 Vial 2 (Male+)(Female+)
+Male: Observed-126 Expected-59; Error%-113.6
+Female: Observed-102 Expected-118; Error%-13.6
WMale: Observed-8 Expected-59; Error%-86.4
WFemale: Observed-0 Expected-0; Error%- 0
Conclusion
The hypothesis we formulated at the begining of the F2 cross, stated that the inheritance of the White-eyed(W) mutation was sex-linked and recessive. The predicted phenotype distrubution for F2 was for vial 1 (MaleW), 25:25:25:25. For vial 2 (Male+), 50(+Female):25(Male+):25(MaleW). Considering the error% calculated between the F2 predictions and outcome, it is reasonable to say that the results of Vial 1 validate our hypothesis, while the results of vial 2 refute it. The disparties exposed through error analysis are very slight in Vial 1, but drastic in Vial 2. Various problems, including both practical human error and genetic discrepancy, could have caused the imbalance recorded in Vial 2. It is most probable that some number of flies were identified erroneously during the preparation of the F2 cross. Failure to properly identify the sex and phenotypes off certain flies would likely result in significant differences from the predicted distribution of phenotypes. Also, it is necessary to note that ideal circumstances would have permitted us to cross Male+ with femaleW in vial 2, rather than Male+ with female+. This all + cross was implemented in order to eviscerate a possible genetic contamination that the outcome of the F1 generation implied. Any sucessful replication of this experiment would be greatly aided by careful selection of Drosophilla sex and phenotype, thus eliminating the need for an all + or any such F2 cross.
Reflecting upon the experiment, several questions arise: what genotypes were present within vial 2, causing such a severe error%, while the results from vial 1 entirely supported our hypothesis? And, is it possible for a cross between + and W flies to result in some sort of incomplete dominance, explaining some of the difficulties encountered when attempting to identify flies from this vial? Regardless of these concerns, it became quantifiably clear through the process of error analysis that, in a controlled experiment free from contamination, our hypothesis of W being a sex-linked recessive mutation stands valid.
Eulogy To Drosophilla
prisoners,
oblivious to what we saw or wanted
in your space,
designed by none other than we
who posed as architecht, and we who shall
say:
leave now, depart and through your lucid
sleep be free
