Introduction
Genetics is the science of heredity and of the mechanisms by which traits are passed from parent to offspring. Which is exactly what our class studied. We took fruit flies as our example/ experiment because of their fast life cycle and their short life span. How that benefited us was we were able to see many generations of the flies. The phenotype (an organism's appearance or other detectable characteristics that results from the organisms genotype and the environment) our group specifically tested was white-eyed fruit flies and wild-eyed fruit flies.
Phenotypes Studied
The three different phenotypes that our class started experimenting with are wild (+), vestigial (vg), and white eyed (w). Wild flies are normal fruit flies with no mutations. Vestigial flies have crippled, malformed wings. White-eyed flies have 'albino characteristics', or white eyes.
Our group is focusing on crossing white-eyed and wild flies. In one vial we crossed wild males with white-eyed females, and in the other we cross white-eyed males with wild females.
Life Cycle Log
3-16-06
Vial I: Flies, no larvae yet.
Vial II: Flies, no larvae yet.
3-17-06
Vial I: Still no larvae. Flies still the same.
Vial II: Still no larvae. Flies still the same.
3-20-06
Vial I: Flies are the same, still no larvae. Medium is dry, added water.
Vial II: Flies are the same, still no larvae. Medium is dry, added water.
3-21-06
Vial I: Some larvae. One fly is dead.
Vial II: Some larvae. Two flies are dead.
3-23-06
Vial I: Larvae and pupae on sides of vial. Dead fly stuck in medium.
Vial II: Larvae and pupae on sides of vial. Dead flies stuck in medium.
3-24-06
Vial I: Lots of pupae, still some larvae left in medium.
Vial II: Same as vial I. We killed all the adult flies yesterday.
3-27-06
Vial I: Lots of pupae still, but many are flies now.
Vial II: still pupae, lots have turned into fruit flies now.
3-30-06
Vial I: Tons of flies. Lots of larvae/pupae. Looks mostly wild, occasionally white.
Vial II: Tons of flies,lots of larvae/pupae. Looks like a good mix of wild& white eyed.
3-31-06
Vial I: Lots&lots of flies dead, flies at the bottom. Still some larvae, still lots of pupae. Small amount of food.
Vial II: Lots& lots of flies. No more larvae, still lots of pupae. not many dead.
F2 starts:
4-3-06
Vial I: One alive. Some larvae.
Vial II: Six alive. Not much larvae.
4-7-06
Vial I: Small amount of larvae, lots of pupae. Two parents alive(have been merged). Water & yeast added.
Vial II: larvae & pupae. All parents died & have been removed. Water & yeast added.
4-17-06
Vial I: A good number of flies. Appears to be all wild. Some larvae & pupae. Medium is brown& black and looks repulsive.
Vial II: Lots of flies, both wild & white. some larvae & pupae. Medium looks brownish- black and disgusting.
4-24-06
Vial I: Lots of flies. Lots & lots of wild & white.
Vial II: large amount of flies mostly wild.
Sexing Fruit Flies
The male flies have "heavy dark bristles" near their abdomen.
Tip of abdomen on males is darker than that on females.
Abdomen of females is much more round than on males.
Sex combs are found on front legs of male flies.
F1 Cross Predictions
Our parent crosses consisted of two vials; vial1 contained wild (+) females and white eyed (w) males, vial2 contained white eyed (w) females and wild (+) males. If their eye color gene is Autosomal and white eye is dominant then both vials will end up 100% heterozygous white eye.
If their eye color is still Autosomal but wild is dominant then both vials will be 100% heterozygous wild.
If eye color is sex-linked and is on the X chromosome then; wild females would be X+ X+, wild males X+ Y, white eyed females Xw Xw and white eyed males Xw Y. If white eyes is dominant and sex-linked with the mutation in females then you will have 100% white eyed offspring; 50% heterozygous (females, Xw X+) and 50% (males, Xw Y). If the white eyes is still dominant but the mutation is now in males then you will get 50% white eyed (heterozygous) females (Xw X+) and 50% wild males (X+ Y). If wild eyes are sex-linked and dominant and the (white eyed) mutation is on the females then the off spring will be 50% wild (heterozygous) females (X+ Xw) and 50% white eyed males (Xw Y). If wild is still dominant but the mutation is on the males the offspring would be 100% wild, 50% females (X+ Xw, heterozygous) and 50% males (X+ Y)
Before we crossed our flies, we made a few predictions about their dominant and recessive traits and whether or not they were sex-linked.
| W | W | |
| + | W+ | W+ |
| + | W+ | W+ |
| w | w | |
| + | +w | +w |
| + | +w | +w |
F1 Outcomes
Our Vial I P Cross resulted in mostly wild and a few white-eyed males with all wild females. It is our belief that we had likely contamination by a white-eyed female which gave us the two different male phenotypes.
Our Vial II P Cross resulted in all white-eyed males and all wild females.
So far, we believe we are observing a sex-linked recessive type of inheritance in our white-eyed mutation.
F2 Predictions
Our predictions show that an F2 cross in our Vial I between Wild Males(X+ Y) and Wild Females(X+ Xw) will result in a 1:1:1:1 genotype ratio. 25% Homozygous Wild Female (X+ X+), 25% Heterozygous Wild Female (X+ Xw), 25% Wild Male (X+ Y), 25% White-Eyed Male (Xw Y). Our phenotype will show a 3:1 ratio. 75% wild (50% female, 25% male) and 25% white-eyed males.
An F2 cross in our Vial II between White-Eyed Males (Xw Y) and Wild Females (X+ X+) will result in the same 1:1:1:1 genotype ratio, but a 1:1 phenotype ratio, 50% white-eyed (25% male, 25% female) and 50% wild (25% male, 25% female).
F2 Outcomes + Fly Counts
Vial I
| Date F2 Counted | Female Wild (+) | Male Wild (+) | Female White-Eyed (w) | Male White-Eyed (w) |
| 4-17-06 | 4 | 12 | 1 | 1 |
| 4-21-06 | 9 | 3 | 0 | 0 |
| 4-24-06 | 92 | 76 | 0 | 19 |
| 4-25-06 | 29 | 28 | 0 | 1 |
| Totals: Overall Vial I | Total Female + 134 | Total Male + 119 | Total Female w 1 | Total Male w 21 |
Vial II
| Date F2 Counted | Female Wild (+) | Male Wild (+) | Female White-Eyed (w) | Male White-Eyed (w) |
| 4-17-06 | 8 | 3 | 5 | 8 |
| 4-21-06 | 1 | 0 | 0 | 0 |
| 4-24-06 | 56 | 42 | 18 | 49 |
| 4-25-06 | 29 | 13 | 6 | 17 |
| Totals: Overall Vial II | Total Female + 94 | Total Male + 58 | Total Female w 29 | Total Male w 74 |
Predictions vs. Actual F2 Outcome (Percent Error)
Vial I
| Phenotype | Observed | Expected | O-E | (O-E)/E | X 100 | % Error |
| Wild Female | 134 | 137.5 | 3.5 | .03 | 3 | 3% |
| Wild Male | 119 | 68.75 | 50.25 | .73 | 73 | 73% |
| White-Eyed Male | 21 | 68.75 | 47.75 | .69 | 69 | 69% |
| White-Eyed Female | 1 | 0 | 1 | Error | 100 | 100% |
Vial II
| Phenotype | Observed | Expected | O-E | (O-E)/E | X 100 | % Error |
| Wild Female | 94 | 63.75 | 30.25 | .47 | 47 | 47% |
| Wild Male | 58 | 63.75 | 5.75 | .09 | 9 | 9% |
| White-Eyed Female | 29 | 63.75 | 34.75 | .55 | 55 | 55% |
| White-Eyed Male | 74 | 63.75 | 10.25 | .16 | 16 | 16% |
