Tuesday
September 30, 2014

Homework Help: Genetics

Posted by qwerty on Wednesday, March 27, 2013 at 1:00am.

β-thalassemia is a human genetic disease that is inherited in an autosomal recessive manner. Individuals with β-thalassemia produce abnormal hemoglobin which results in a reduced ability to carry oxygen in their blood. The severity of symptoms depends on several genetic and environmental factors and can vary from mild to fatal.

In this problem, we will use the letter "A" to represent the normal allele and the letter "a" to represent the β-thalassemia allele.

a) In Delhi, India, the frequency of the a allele is 0.03. Using the mathematics from lecture, estimate the following:

i)The frequency of β-thalassemia carriers (genotype Aa) in the Delhi population. Please express your answer as a number between 0.0000 and 1.0000. You may use as many significant digits as necessary.

ii)The frequency of people with β-thalassemia (genotype aa) in the Delhi population. Please express your answer as a number between 0.0000 and 1.0000. You may use as many significant digits as necessary.

b) Individuals with β-thalassemia are often partially resistant to malaria, a severely debilitating disease. Malaria is common in Delhi, India. In contrast, malaria is extremely rare in Iceland. Based on this, would you expect the frequency of the β-thalassemia allele to be higher, lower, or the same in Iceland as compared to Delhi?

Higher in Iceland than DelhiThe same in both placesLower in Iceland than Delhi

c) In Sardinia, approximately one in every 200 people has β-thalassemia. Using the mathematics from lecture, estimate the following:

i)The frequency of the β-thalassemia allele in the Sardinian population. Please express your answer as a number between 0.0000 and 1.0000. You may use as many significant digits as necessary.

ii)The frequency of β-thalassemia carriers (genotype Aa) in the Sardinian population. Please express your answer as a number between 0.0000 and 1.0000. You may use as many significant digits as necessary.

iii) Consider the following situation in the Sardinian population. An individual with β-thalassemia marries an unaffected individual of unknown genotype. On average, considering many such couples, what is the chance that their first child will have β-thalassemia? Please express your answer as a number between 0.0000 and 1.0000. You may use as many significant digits as necessary.

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In population genetics, we deal with traits in large groups of humans. We therefore use frequencies of alleles and genotypes rather than the genotypes of individual humans.

For a gene with two alleles, A and a, we can define:

p = the frequency of the A allele
q = the frequency of the a allele

Since there are only these two alleles, p + q = 1 always.

We can often make the following approximations:

The frequency of AA individuals = p2
The frequency of Aa individuals = 2pq
The frequency of aa individuals = q2

We will make these assumptions

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