Question 1a: Genes A, B, and C are linked as shown below. A and B are 10 m.u. ap

Question

Question 1a:

Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while B and C are 20 m.u. apart. All dominant alleles are on one homologue and all recessive alleles are on the other homologue. Which genotype and probability is correct for a crossover occurring between A and B?

Question 1b:

Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while B and C are 20 m.u. apart. All dominant alleles are on one homologue and all recessive alleles are on the other homologue. Which genotype and probability is correct for a crossover occurring between B and C?

Question 1c:

Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while B and C are 20 m.u. apart. All dominant alleles are on one homologue and all recessive alleles are on the other homologue. Which genotype and probability is correct for a double crossover?

Question 1d:

Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while B and C are 20 m.u. apart. All dominant alleles are on one homologue and all recessive alleles are on the other homologue. Which genotype and probability is correct for no crossing over?

Question 1e:

Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while B and C are 20 m.u. apart. All dominant alleles are on one homologue and all recessive alleles are on the other homologue. Out of 1,000 total offspring, you expect 20 offspring to come from a double crossover, but you observe only 15 offspring. What is the interference?

Explanation / Answer

Answer:

1a). Abc = 0.05

Explanation:

A---B---C / a---b---c

Distance between the genes = Recombination frequency

10 m.u. = 10% recombination frequency

If single crossover occurs between a & b, it produces two types of genotypes, i.e., Abc & aBC with 5% each.

So genotype Abc probability = 5% = 0.05

And genotype, aBC probability = 5% = 0.05

1b). ABc = 0.10

Explanation:

A---B---C / a---b---c

Distance between the genes = Recombination frequency

20 m.u. = 20% recombination frequency

If single crossover occurs between b & c, it produces two types of genotypes, i.e., ABc & abC with 10% each.

So genotype ABc probability = 10% = 0.1

And genotype, abC probability = 10% = 0.1

1c). aBc=0.01

Explanation:

Double crossover frequency = Single crossover frequency between a&b * Single crossover frequency between b&c

= 10%*20% = 0.0002

Double crossover genotypes, AbC (0.01) & aBc (0.01)

1d). abc = 0.34

Explanation:

All recombinants = 0.1 + 0.2 + 0.0002 = 0.0302

1- 0.3002 = 0.6998

Noncross over genotypes = ABC (0.34) & abc (0.34)

1e). 0.25

Explanation:

Expected double crossover frequency = 20/1000 = 0.02

Observed double crossover frequency = 15/1000 = 0.015

Coefficient of coincidence = 0.015/0.02 = 0.75

Interference = 1-Coefficient of coincidence

= 1-0.75 = 0.25

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