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Genotype Frequencies

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In a human population of 1000 people at a blood locus there are two alleles M and N. The observed genotype frequencies at this locus are f(MM) = 0.26, f(MN) = 0.35, and f(NN) = 0.39.

a. What is the frequency of each allele in this population? Do not assume Hardy-Weinberg equilibrium.

b. Based on the answer above calculate the expected frequencies of all genotypes at this locus assuming HW equilibrium.

Is the population in HW equilibrium? Explain your answer by doing a statistical analysis.

Give three criteria that must be fulfilled by a population, before it can be assumed it is in HW equilibrium? Explain why for each.

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Solution Preview

The allele frequency refers to the frequency by which the individual allele (M vs. N) shows up.
The equation to determine allele frequency uses the genotypic frequencies of the homologus genes:

pM = f(MM) + 0.5[f(MN)] = 0.26 + 0.5(35) = 0.435

Similarly:

pN = f(NN) + 0.5[f(MN)] = 0.39 + 0.5(35) = 0.565 (or you could just do 1 - pM = pN since there are only two alleles)

The HW equilibrium assumes that:

p^2 + 2pq + q^2 = 1

where p = f(MM), q = f(NN) and 2pq = f(MN)

This essentially creates a mathematical model which predicts the general distribution of homozygous and heterzygous organisms, of which the ...

Solution Summary

The frequency of each allele in the populations are determined. Hardy-Weinberg equilibrium is analyzed.

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Genetic variation and disease

1 Define the term "genetic variation."

If a gene or locus has two alleles (A and a) in a population, what are all the possible genotypes?

If the frequency of (A) allele = p, and the frequency of (a) allele is q, what is the frequency of all possible genotypes in this population?

2 What is the Hardy-Weinberg equilibrium?

In a population, a locus A has two alleles (A) and (a). The frequency f of (A) is f (A) = 0.6; what is the f (a)?

Using these frequencies, calculate the frequencies of all possible genotypes in a population in Hardy-Weinberg equilibrium.

3 In a population (Z), the frequencies of genotypes of a two allele locus (B and b) are f(BB) = 0.3, f(bb) = 0.6, f (Bb) = 0.1. Calculate the frequencies of both alleles.

Using the allele frequencies calculated in a., calculate the frequencies of all possible genotypes at this locus in a population after one generation of random mating.

Is the population (Z) in part a above in Hardy-Weinberg equilibrium? The population size is 1000.

4 Describe how you would use the Hardy-Weinberg equilibrium to calculate genotype frequencies of a locus with three alleles.
If the f(D) of an X-linked gene in a population = 0.8, what is the f(d) of the other allele at this locus?

What is the frequency of females' homozygous for d allele (XdXd)?

What is the frequency of males' hemizygous for the d allele (XdY)?

5 Explain why more males present with X-linked recessive diseases. Show your reasoning.

Why must the five assumptions/criteria apply to a population before we can say it is in Hardy-Weinberg equilibrium?

Take any one of these assumptions and explain in detail how it could disrupt the Hardy-Weinberg equilibrium for a particular gene locus.

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