Drosophila Report
Introduction
Heredity is the means by which an offspring obtains their parents qualities, or the simple passing of genetic factors from parent to offspring. Heredity plays a significant role in Mendel’s laws and Mendel’s findings. Mendel’s findings were also a big influence on many others interested in the hereditary area of biology. Mendel developed 3 laws to explain certain instances of heredity. The first law is called The Law of Segregation, which is when offspring receive one genetic allele from each parent during fertilization when sex cells bond (Concept 1). The second law is known as The Law of Independent Assortment, which states the inheritance of one pair of genes is independent of the inheritance of another pair. The third and last law is called The Law of Dominance, which says that in a heterozygote, one trait will inhibit the presence of another trait for the same characteristic (Lumen).
These laws are all significant to our Drosophila project, as these laws were tested with generations of Drosophila flies in a lab setting. An experiment was conducted by crossing certain fly types, followed by taking observations on the offspring observable phenotypes. We tested a total of two crosses with their respective reciprocal crosses as well. The first was a monohybrid cross of male white-eye with a female wild type, and the reciprocal male wild type with female white-eye. This cross was expected to have a 3:1 ratio, with 3 wild type to 1 white eye. The second cross was a dihybrid between the male wild-eye/vestigial wing with the female sepia-eye/wild wing, and their reciprocal cross of male sepia-eye/wild wing with female wild-eye/vestigial wing. This cross was expected to have a 9:3:3:1 ratio, with 9 normal wing/red eye, 3 vestigial wing/red eye, 3 normal wing/sepia eye, and 1 vestigial wing/sepia eye.
Methods
For the first step, two vial tubes were prepared with a with a sponge cover for the D. melanogaster to live and mate in, and these tubes consisted of a powdered media, reagent blue, and dried yeast pellets as a food source. The monohybrid was then crossed in the first vial, which was Male White-Eye with Female Wild-Eye. The dihybrid was cross in the second vial, which was male wild eye/vestigial wing with female sepia-eye/wild wing. Flies from each type were transferred into the first vial tube with the blue media, this was done using the FlyNap to anesthetize the flies. After a week, the D. melanogaster would have mated and eggs will have hatched to make the F1 generation. The parents were to be humanely euthanized to avoid backcross with the F1 generation. After another week, the F1 offspring generation were put to sleep with FlyNap and counted. The first cross was counted by the sex and eye type of the D. melanogaster. The second cross was counted by eye color and wing type.
After the flies were counted, they were put back into new vials so they would be able to mate again for the week. After that week, the F1 generation flies were removed from the vials and the larvae left behind were to be the F2 generation. These F2 larvae were left for another week to mature. After this week, the F2 were finally counted once again using the same methods as F1. When all counts were finished for both generations, the Chi-square and the p-values were computed to test the distribution of the phenotypes.
Results
Monohybrid Cross
For the Male White-Eye and Female Wild-Eye monohybrid cross, the F1 resulted in 0 Male White-Eye, 0 Female White-Eye, 1622 Male Wild-Eye, and 1644 Female Wild-Eye. The F2 of this cross resulted in 851 Male White-Eye, 24 Female White-Eye, 823 Male Wild-Eye, and 1597 Female Wild-Eye.
TABLE 1: Female White Eye X Male Wild Eye
F1
F1
F1
Male White Eye
Female White Eye
Male Wild Eye
Female Wild Eye
708
0
3
725
F2
F2
F2
Male White Eye
Female White Eye
Male Wild Eye
Female Wild Eye
894
876
843
857
3470
Next, for the reciprocal Male Wild-Eye and Female White-Eye, we got 708 Male White-Eye, 0 Female White-Eye, 3 Male Wild-Eye, and 725 Female Wild-Eye. For the F2 of this cross, we got a total of 894 Male White-Eye, 876 Female White-Eye, 843 Male Wild-Eye, and 857 Female Wild-Eye.
TABLE 2:Female Wild Eye X Male White Eye
F1
F1
F1
Male White Eye
Female White Eye
Male Wild Eye
Female Wild Eye
0
0
1622
1644
F2
F2
F2
Male White Eye
Female White Eye
Male Wild Eye
Female Wild Eye
851
24
823
1597
3295
Dihybrid Cross
For the Wild-Eye/Vestigial Wing and Sepia-Eye/Wild Wing, the F1 gave us 2476 Wild Wing/Wild-Eye and 0 for the rest of the phenotypes. The F2 generation gave us 2670 Wild Wing/Wild-Eye, 877 Wild Wing/Sepia-Eye, 856 Vestigial Wing/Wild-Eye, and 287 Vestigial Wing/Sepia-Eye.
TABLE 3:Vestigial Wing, Wild Eye X Wild Wing, Sepia Eye
F1
F1
F1
Wild Wing, Red Eye
Wild Wing, Sepia Eye
Vestigial Wing, Wild Eye
Vestigial Wing, Sepia Eye
2467
0
0
0
F2
F2
F2
Wild Wing, Red Eye
Wild Wing, Sepia Eye
Vestigial Wing, Wild Eye
Vestigial Wing, Sepia Eye
2670
877
856
287
4690
Expected values:
Wild wing, Red Eye
4690*(9/16)= 2638.125
Wild wing sepia eye
4690*(3/16)= 879.375
Vestigial wing wild eye
4690*(3/16)= 879.375
Vestigial wing sepia eye
4690*(1/16)= 293.125
Chi square formula: x2=∑(O – e)e)2
X2
Wild Wing, Red Eye
.3851
Wild Wing Sepia Eye
.0064
Vestigial Wing Wild Eye
.6213
Vestigial Wing Sepia Eye
.1279
Total X2 =
1.1407
Degrees of freedom (Df): n – 1 = 4 – 1 =3
P > 0.1
The p-value is in between 0.5 and 0.9, thus, the hypothesis is not declined.
Discussion
We hypothesized that through the first cross we would get a 100% wild type in the 3:1 ration for the F1, and F2 would result in a 9:3:3:1 ratio as well. As expected, we did get the 100% wild type (for both traits) in the F1, and results also gave us a 9:3:3:1 ratio for the F2. Our calculations for the X2 of this dihybrid cross were also satisfactory, with a total X2 of 1.14
To test Mendel’s Law of Segregation, we observed the cross between Wild-Eye and White-Eye. Wild-Eye was the dominant allele while the White-Eye was the recessive. Our experiment did result in the 3:1 ratio that was expected, so this shows that confirmation for the Law of Segregation. To test Mendel’s Law of Independent Assortment, we observed the cross between Wild-Eye/Vestigial Wing and Sepia-Eye/Wild Wing. The results showed that the Wild Types were dominant over the Sepia/Vestigial, as they were the only ones shown in the F1 cross. The results of F2 showing the 9:3:3:1 ratio supported Mendel’s Law of Independent Assortment.
All in all, the results of our experiments show how heredity come into play. We were able to observe Mendel’s laws first hand when it came to the results of our tests. This shows how significant Mendel’s findings were, and how important they continue to be.