You are trying to calculate the map distances between three genes in Dragonflies
ID: 196134 • Letter: Y
Question
You are trying to calculate the map distances between three genes in Dragonflies. The gene extrawings (ex) produces an extra pair of wings and is recessive to the wild-type four wings (ex+). The gene eyeless (ey) causes the eyes not to form properly and is recessive to the wild-type normal eyes (ey+). The gene blue (b) causes the body to be a neon blue color and is recessive to the wild-type black (b+). A heterozygous dragonfly is crossed to a tester male and the following progeny are obtained: 321 with extra wings and no eyes, 284 with blue bodies, 72 with extra wings, 69 with blue bodies and no eyes, 27 with extra wings and blue bodies, 21 with no eyes, and 4 wild-type.
What is the distance in cM between extrawings and eyeless? (Please answer to two decimal places)
What is the interference?
Explanation / Answer
Answer:
Distance between extrawing and eyeless = 21.13 cM
Interference = 0.39
Explanation:
321 with extra wings and no eyes---ex b+ ey
284 with blue bodies---ex+ b ey+
72 with extra wings---ex b+ ey+
69 with blue bodies and no eyes---ex+ b ey
27 with extra wings and blue bodies---ex b ey+
21 with no eyes---ex+ b+ ey
4 wild-type---ex+ b+ ey+
2 extra wings, blue bodies, no eyes---ex b ey (It is not given in the question)
800--Total
Hint: Always recombinant genotypes are smaller than the non-recombinant genotypes.
Hence, the parental (non-recombinant) genotypes is ex b+ ey / ex+ b ey+
1).
If single crossover occurs between ex & b+..
Normal combination: ex b+ / ex+ b
After crossover: ex b/ex+ b+
ex b progeny= 27+2=29
ex+ b+ progeny = 21+4=25
Total this progeny = 54
The recombination frequency between ex&b+ = (number of recombinants/Total progeny) 100
RF = (54/800)100 = 6.75%
2).
If single crossover occurs between b+ & ey..
Normal combination: b+ ey / b ey+
After crossover: b+ ey+ / b ey
b+ ey+ progeny= 72+4=76
b ey progeny = 69+2=71
Total this progeny = 147
The recombination frequency between b+&ey = (number of recombinants/Total progeny) 100
RF = (147/800)100 = 18.38%
3).
If single crossover occurs between ex & ey..
Normal combination: ex ey / ex+ ey+
After crossover: ex ey+/ex+ ey
ex ey+ progeny= 72+27=79
ex+ ey progeny = 69+21=90
Total this progeny = 169
The recombination frequency between ex & ey = (number of recombinants/Total progeny) 100
RF = (169/800)100 = 21.13%
Recombination frequency (%) = Distance between the genes (cM)
ex----------6.75cM--------b-----------18.38cM--------------ey
Expected double crossover frequency = (RF between ex & b) * (RF between b & ey)
= 6.75% * 18.38% = 0.0124
The observed double crossover frequency = 4+2 / 800 = 0.0075
Coefficient of Coincidence (COC) = Observed double crossover frequency / Expected double crossover frequency
= 0.0075 / 0.0124
= 0.61
Interference = 1-COC
= 1-0.61 = 0.39
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