Genetics

Topics: Allele, Dominance, Gene Pages: 13 (1078 words) Published: March 22, 2014
EXTENTION OF MENDELIAN INHERITANCE
Objective
The objectives of this experiment were to observe Mendel’s law with inheritance trait of the curly wing mutation and the interactions between the mutant genes of vestigial wings and curved wings in Drosophila.

Results
Part A
Cross A (wildtype females X curly males)

Male
Female
Wild type
1
2
Curly wing
0
1
Table 1. The number of the phenotypes and sex of offspring of the Cross A Cross B (curly females X curly males)

Male
Female
Wild type
2
1
Curly wing
3
0
Table 2. The number of the phenotypes and sex of offspring of the Cross A 2. The cross A and B look like sex-linked traits, but it is not sex-linked dominant curly wing mutation and sex-linked recessive curly wing mutation. Thus, the curly wing genes have to be on an autosomal chromosome because the cross A showed wild type female reveals the sex-linked recessive, and the cross A had wild type females reveals the x-linked dominant at the same time in part A. 3.

Parent
P1
P2
Genotype
aa
Aa
Phenotype
Wild
Curly wing
*Wild type allele: a
*Curly wing allele: A

Punnet Square

Cross A
P1
P2
a
a
A
Aa
Aa
a
aa
aa

F1 Genotype
aa
Aa
F1 phenotype
Wild type
Mutant
Phenotype ratio
1
1

Cross B (P2 and P2)
P2
P2
A
A
A
Aa
Aa
A
Aa
A A

F1 Genotype
Aa
Aa
AA
F1 Phenogype
Wild type
Mutant
Lethal
Phenotype ratio
1
2
0

Theoretically, the proportion of the offspring from Cross A should be 1:1, and the proportion of the offspring from Cross B should be 1:2.

4.

Observed
Expected
O - E
(O – E)2
(O –E)2/E
A A
Lethal
0
0
0
0
A a
3
4
-1
1
0.25
a a
3
2
1
1
0.5
Total
6
6

0.75, p value is between 0.5 and 0.7. Thus, the difference between observation and expectation can be accepted.

Part B
F2
Wild Type
Veinlet
Vestigial
Veinlet/Vestigial
G11
1 Female/1 Male
1 Male
-
-
G12
1 Male
1 Female
1 Female
-
G13
1 Female / 1 Male
1 Female
-
-
G14
-
2 Female / 1 Male
-
-
G15
1 Male
-
1 Female / 1 Male
-
G16
2 Male
1 Female
-
-
G17
2 Female
-
1 Male
-
G18
1 Female / 1 Male
1 Male
1 Female
-
G19
1 Female
1 Female
1 Male
-
G20
1 Female /2 Male
-
1 Male
-
Total
7 Female / 9 Male
6 Female / 3 Male
3 Female / 4 Male
-
Table 3. The number of the phenotypes and sex of the F2 generation

1 The mutant vestigial and vienlet wings are observed as recessive traits because only wild type wings are observed in F1 generation.

2 From individual count, we observed 2 male and 1 female wild type wings, no veinlet wing and 1 male vestigial wing. It seemed like there is not a sex difference in our result because 2 males and 1 female are wild type, and only 1 male showed vestigial wing. However the individual sample size was so small. From the all group result of lab showed the mutation is not a sex difference.

3 The F2 ratio is almost like 2 wild type, 1 vienlet and 1 vestigial. It would seem that there is a recessive epistasis interaction between the two recessive mutant genes (Cordell, 2002), with the vestigial gene being epistasis to the veinlet gene. Thus when the genotype is homozygous recessive, the vestigial gene expression would mask the veinlet gene expression. While the wild type is actually a complementary gene interaction between the 2 normal dominant gene. As we can see in the next question

4
Parental
P3
P4
Phenotype
Vestigial
Veinlet
Genotype
aaBB
AAbb
F1 Genotype
AaBb
F1 Phenotype
Wild type

F1 inter-crossed

AB
Ab
aB
ab
AB
AABB
AABb
AaBB
AaBb
Ab
AABb
AAbb
AaBb
Aabb
aB
AaBB
AaBb
aaBB
aaBb
Ab
AaBb
Aabb
aaBb
aabb

F2 Genotype ratio
9 A_B_
3A_bb
3 aaB_
1 aabb
F2 Phenotype ratio
9 Wild type
3 Vienlet
3 Vestigial
1 Veinlet / vestigial

However, from the observation, no veinlet and vestigial drosophila is observed. Therefore, we can guess the recessive alleles may be lethal or the aa alleles are epistatic to the...
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