Question 1 [18 marks / 18 minutes] Two Drosophila flies with wildtype (transpare
ID: 261389 • Letter: Q
Question
Question 1 [18 marks / 18 minutes]
Two Drosophila flies with wildtype (transparent, long) wings were mated. In the progeny, two new phenotypes appeared: dusky wings and clipped wings. The progeny were as follows:
Females: 179 transparent, long
58 transparent, clipped
237
Males: 92 transparent, long
89 dusky, long
28 transparent, clipped
31 dusky, clipped
240
Use the following symbols to answer the questions below:
d for dusky wings, and d+ for wildtype wings (transparent)
c for clipped wings, and c+ for wildtype wings (long).
a) The mode of inheritance of the clipped phenotype is autosomal recessive. Explain how the data shown above support this statement. [2 marks]
b) The mode of inheritance of the dusky phenotype is X-linked recessive. Explain how the data shown above support this statement. [2 marks]
c) Give the genotypes of the parents showing both genes together (symbols defined above). [4 marks]
d) Use a Punnett square to show the genotypes and phenotypes of the different progeny classes (both genes together), comparing predicted ratios with observed ratios. 10 marks
Explanation / Answer
A) Presence of two recessive allele is necessary to express clipped phenotype. Each parent carry one recessive allele. Because to express the recessive phenotype, offspring should get one recessive allele from each parent.
B) Male have one X and one Y chromosome while female have two X chromosome. To express X linked recessive phenotype, female offspring have to get one recessive X chromosome from each parent. But male offspring with one recessive X allele can express the recessive phenotype.
C) d : dusky wings, d+ : wildtype wings (transparent), c : clipped wings, c+ : wildtype wings (long).
clipped phenotype is autosomal recessive
dusky phenotype is X-linked recessive
Male genotype : Xd+ Y/ c+c
Female genotype : Xd+ Xd / c+ c
D)
Female : 8 chances
Total female = 237
5/8 = transparent, long
(5/8) x 237 = 148 (Expected)
Observed = 179
3/8 = transparent, clipped
(3/8) x 237 = 89 (Expected)
Observed = 58
Male : 8 chances
Total male = 240
transparent, long = (3/8) x 240 = 90 (Expected) : Observed = 92
transparent, clipped = (1/8) x 240= 30 (Expected) : Observed = 28
dusky, long = (2/8) x 240 = 60 (Expected) : Observed = 89
dusky, clipped = (2/8) x 240 = 60 (Expected) : Obseved = 31
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