14 December 2012
Examination of Mendelian Genetics by crossing Wild Type and Apterous Drosophila melanogaster
NAME
CLASS
TEACHER
DATE
14 December 2012
Examination of Mendelian Genetics by crossing Wild Type and Apterous Drosophila
melanogaster
Fruit Flies are something that are common in almost every house hold in the world, but
who knew that there were so many variations and mutations that could show up within their
species? Who thinks about flies that can’t fly? Drosophila melanogaster are actually more
complex than most people think. They have an estimated 14,000 genes that are carried on8
chromosomes. There are many variations and mutations in flies that affect everything from eye
color to body color to if they do or do not have wings. There is even a mutation that can cause
flies to have legs as antennas.
In this lab, we explore the ways that specific genetic traits are passed on by breeding and
crossing flies. We used Mendelian Genetics as a model, and tried to find if the monohybrid
autosomal crosses that we did with the flies follows the ratios that Mendel found with his pea
plants. We hypothesized that the monohybrid autosomal recessive cross would fit into Mendel’s
genetic ratios of 1:0 in the F1 and 3:1 in the F2. The trait that we looked at was wings, wild type
meaning they have wings and apterous meaning they have no wings. We do this by creating are
F1 and F2 generation crossing the flies processed and studying the outcome.
Materials:
-Vials
-Fly Food
-Water
-Apterous and Wild Type Flies
14 December 2012
-Yeast
-Fly Nap
Methods:
1) After obtaining all of the materials for this experiment, we set up two vials where we
grew flies. We put a scoop of fly food into the vial and added an equal amount of water
and let the food soak up the water; the food turned blue. Then, we added about four
grains of yeast to the vial, just dropped into the food. The yeast prevents mold from
growing on the food.
2) We added apterous flies to one vial and wild type flies to the other vial. Be careful not to
drop the flies into the food, they will get stuck and die if that happens. We used 5 wild
type and 12 apterous, making sure to have both genders in each vial. Then we waited for
the flies to reproduce. Once we saw larva, we killed the parent flies with assistance from
Fly Nap. The larva that we saw at this stage became the P Generation, or the Parental
Generation.
3) Once the larva morphed into flies, we took the female from the apterous vial, doing the
best we could to make sure that they were virgin flies, and the males from the wild type
vial and put them into a new vial (repeating the process in step 1) to reproduce to make
the F1 Generation.
4) Once again, as soon as we saw larva, we killed the parents. Then we waited for the larva
to morph into flies, but this time, using the Fly Nap to knock-out the flies, we counted
them (killing them after counting). We also took 3 males and 3 females and put them into
a new vial (repeating the process from step 1) to reproduce and create the F2 Generation.
14 December 2012
5) As soon as we saw larva in the F2 vial, we killed the parents and waited for the larva to
become flies. Once they did, we used the fly nap to knock them out and count them (kill
them after counting)
6) Count the flies until the numbers being to slow down. Clean out vials.
Data:
We followed the procedure above and our group counted 251 wild type flies and 0 apterous flies
in the F1 generation. In our F2 Generation, we counted 99 wild type and 23 apterous.
Class Results:
Parental Generation: BB x bb
F1
Expected Outcome: ALL WILD
Group 1
Wild Type
Group 2
Group 3
Group 4
Group 5
Group 6
TOTAL
251
132
172
118
220
0
761
0
0
0
0
0
130
0
Apterous
*Totals exclude the data from groups 2 and 6
F2
Expected Outcome: 3:1 Ratio of Wild Type: Apterous
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
TOTAL
Wild Type
99
97
146
121
83
0
449
Apterous
23
0
27
32
29
237
111
*Totals exclude the data from groups 2 and 6
14 December 2012
Chi-Squared:
F1(class): 761:0 fits Mendel’s 1:0 ratio for monohybrid recessive cross of homozygous recessive
and homozygous dominant.
Observed
Wild Type
Expected
Deviation
Deviation^2/Expected
Deviation^2
761
761
0
0
0
0
0
0
0
0
Apterous
Total: 761
Chi-squared = 0
Degrees of freedom = 1
Probability = 0.5
Fail to reject the null hypothesis.
F2 (class): 449:111 fits Mendel’s 3:1 ratio for monohybrid heterozygous cross.
Observed
Expected
Deviation
Deviation^2
Deviation^2/Expected
Wild Type
449
420
29
841
2.00
Apterous
111
140
-29
841
6.01
Total: 560
Chi-squared = 8.01
Degrees of freedom = 1
Probability = 0.5
Reject the null hypothesis.
F2 (my group): 449:111 fits Mendel’s 3:1 ratio for monohybrid heterozygous cross.
14 December 2012
Observed
Expected
Deviation
Deviation^2
Deviation^2/Expected
Wild Type
99
91.5
7.5
56.25
.615
Apterous
23
30.5
-7.5
56.25
1.84
Total: 122
Chi-squared = 2.46
Degrees of freedom = 1
Probability = 0.5
Fail to reject the null hypothesis.
The goal of this experiment was to track the genetics of Drosophila melanogaster and see
how the ratios that were produced compared to the ratios that Mendel found. We hypothesized
that the outcome of our experiment would support the 1:0 and 3:1 ratios the Mendel found. Our
hypothesis was supported for the most part. It was supported by the product of the chi-squared
test for the F1 class data and the F2 group one (my group’s) data. I say that it was somewhat
supported because the F2 class chi-squared test rejected the null hypothesis, so it does not fit the
3:1 ratio, but the chi-squared test shows that there are other influences that affected the results
that were not intentional. To improve this experiment the people doing it would need to be better
able to get virgin flies, I think that this was our biggest issue in this experiment. To fix this you
would need someone that was able to devote more of their time to the flies to remove them as
soon as possible after they hatch to help ensure the virginity of the female flies. Over all I feel
that the experiment was a success; my group specifically was successful with supporting the
Mendelian genetic ratios.