Drosophilia Cross lab report

Topics: Gamete, Genetics, Male Pages: 8 (609 words) Published: March 28, 2014

March 14th, 2014
Empirical Analysis of Mendel’s Laws

Objective:
To determine if Mendel’s law of segregation and independent assortment genetic principle’s hold true by observing the genotypes of both the F1 and F2 generation of Drosophilia Melanogaster flies and applying the Chi Square analysis to the F2 offspring to see if the our results fall inside or outside statistical variation.

Methods:
This experiment was carried out over a five-week process. Each lab bench crossed two parental generations: dumpy females x sepia males, and sepia females x dumpy males. My partner and carried out the sepia x dumpy cross.

The following week (week 2), we removed the parents so we wouldn’t confuse the P generation with the eventual F1 offspring.
Week 3 we reevaluated our vials, sans the P generation, and classified and counted the F1 flies, separating them into male and female, noting their specific phenotypes. Following classification, we crossed 3 virgin F1 generation females with 5 F1 generation males. Additionally, we also performed a backcross consisting of externally added dumpy, sepia virgin females x F1 males.

During week 4, we removed the parents once more. This time, the parents were the F1 generation.
Finally, in week 5, we reexamined our vials, classifying and counting the newly acquired F2 generation as well as the backcross to determine phenotype and sex. We were then able to discard our vials and record our F2 results. Our results were to tell us whether or not Mendel’s laws held true.

Results from Fly Cross (lab section 13):
Table 1: Phenotypes of F1 generation
F1 Generation (all wild-type)

Female
Male
Total
Sepia x Dumpy
47
62
109
Dumpy x Sepia
59
55
114

Table 2 & 3: Phenotype of F2 generation (entire lab section) F1 x F1 cross (from dumpy x sepia)

Female
Male
Total
Wild-type
32
54
86
Dumpy
10
25
35
Sepia
7
12
19
Dumpy & Sepia
2
4
6

51
95
146

Chi Square test for F1 x F1 cross (from dumpy x sepia)

Wild-type
Dumpy
Sepia
Dumpy & Sepia
Total
Observed
86
35
19
6
146
Expected
82.1
27.4
27.4
9.1
146
[(o-e)2/e]
0.18
2.11
2.57
1.06
X2 = 5.92

Table 3:
F1 x F1 cross (from sepia x dumpy)

Female
Male
Total
Wild-type
44
47
91
Dumpy
19
22
41
Sepia
40
33
73
Dumpy & Sepia
23
29
52

126
131
257

Chi Square test for F1 x F1 cross (from sepia x dumpy)

Wild-type
Dumpy
Sepia
Dumpy & Sepia
Total
Observed
91
41
73
52
257
Expected
144.6
48.2
48.2
16.1
257
[(o-e)2/e]
19.87
1.08
12.76
81.0
X2 = 114.71

F1 x F1 cross (sepia x dumpy; own data)

Female
Male
Total
Wild-type
11
15
26
Dumpy
5
6
11
Sepia
2
3
6
Dumpy & Sepia
0
2
2

18
26
42

F1 x sepia & dumpy (backcross)

Female
Male
Total
Wild-type
79
88
167
Dumpy
35
36
71
Sepia
51
53
104
Dumpy & Sepia
27
29
56

Chi square test for F1 x sepia & dumpy (backcross)

Wild-type
Dumpy
Sepia
Dumpy & Sepia
Total
Observed
167
71
104
56
398
Expected
99.5
99.5
99.5
99.5
398
[(o-e)2/e]
45.79
8.16
0.20
19.02
X2 = 73.17

Discussion:
In 1866, Gregor Mendel published a paper entitled, “Experiments on Plant Hybrids” that forever changed modern genetics. Included in this publication were two Mendelian principles. The first principal is in regards heredity and states, “two alleles for each trait separate (segregate) during gamete formation, and then unite at random, one from each parent, at fertilization. This is deemed the law of segregation. To go along with this general rule of thumb, Mendel also considered the potential for shuffling of genes during di-hybrid crosses. When there are two individual genes in play, their inheritance pattern act completely independent from one another. Thus, “during gamete formation, different pairs of alleles segregate independently of each other.”

Mendel spent years inside the lab in order to confidently claim these two laws of genetics, and...
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