Question 1 (15 points) You are tracking three loci in the fruit fly, locis A, B,

Question

Question 1 (15 points)

You are tracking three loci in the fruit fly, locis A, B, and C, and want to know whether the loci are linked and if so what their physical distances are from one another as well as the physical order they are in. To find out this information you perform a three-point testcross with a fly that is heterozygous for all three alleles. The progeny of this cross are:

Genotype

Number of individuals

389

410

39

44

77

83

6

5

TOTAL

1053

(a) What is the recombination frequency between loci A and B?

(b) What is the recombination frequency between loci B and C?

(c) What is the recombination frequency between loci A and C?

(d) Are these loci linked?

(e) Demonstrate the physical arrangement of the genes on the chromosome, i.e. the order of the genes on a chromsosome as well as their map distances.

(f) Write out the genotypes of the parents for this cross, indicating which alleles are linked with one another for each parent?

________________________________ X ____________________________________

Genotype

Number of individuals

a/a B/b C/c

389

A/a b/b c/c

410

a/a b/b C/c

39

A/a B/b c/c

44

a/a b/b c/c

77

A/a B/b C/c

83

a/a B/b c/c

6

A/a ;b/b C/c

5

TOTAL

1053

Explanation / Answer

1. recombination frequency between A AND B ---- 83+44+39+410 = 576 /1053 * 100 = 54.7 %.

2. recombination frequency between B and C = 389+39+410+44 = 882 / 1053 *100 = 83.76%.

3. R.F between A and C = 410 + 77 +39+6 = 532 / 1053 * 100 = 50.52%

R.F OF A and B = 54.7 %

B AND C = 83.7%

C AND A = 50.52%

, NO gene is linked because their recombination frequency is too high but there are gene may be present in same chromosome or different chromosome.

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