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Ch. 26 - Population and Evolutionary Genetics
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 26 - Population and Evolutionary GeneticsProblem 6a
Chapter 26, Problem 6a

Consider rare disorders in a population caused by an autosomal recessive mutation. From the frequencies of the disorder in the population given, calculate the percentage of heterozygous carriers:
0.0064

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1
Identify the given frequency of the disorder in the population, which represents the frequency of individuals who are homozygous recessive (q²). In this case, q² = 0.0064.
Calculate the allele frequency of the recessive allele (q) by taking the square root of q²: \(q = \sqrt{q^{2}}\).
Determine the frequency of the dominant allele (p) using the relationship \(p + q = 1\), so \(p = 1 - q\).
Calculate the frequency of heterozygous carriers (2pq) using the formula for heterozygotes in Hardy-Weinberg equilibrium: \$2pq = 2 \times p \times q$.
Convert the frequency of heterozygous carriers to a percentage by multiplying the result by 100.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Autosomal Recessive Inheritance

Autosomal recessive disorders require two copies of a mutant allele for the phenotype to be expressed. Individuals with only one mutant allele are carriers and typically do not show symptoms. Understanding this inheritance pattern is essential to relate genotype frequencies to disease prevalence.
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Hardy-Weinberg Equilibrium

The Hardy-Weinberg principle provides a mathematical framework to relate allele and genotype frequencies in a population under random mating and no evolutionary forces. It allows calculation of carrier frequencies from disease prevalence using the equation p² + 2pq + q² = 1.
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Calculating Carrier Frequency from Disease Prevalence

For an autosomal recessive disorder, the disease frequency corresponds to q² (homozygous recessive). The carrier frequency is 2pq, where p ≈ 1 for rare alleles. By taking the square root of disease frequency to find q, one can estimate the percentage of heterozygous carriers.
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Related Practice
Textbook Question

Price et al. [(1999). J. Bacteriol. 181:2358–2362] conducted a genetic study of the toxin transport protein (PA) of Bacillus anthracis, the bacterium that causes anthrax in humans. Within the 2294-nucleotide gene in 26 strains they identified five point mutations—two missense and three synonyms—among different isolates. Necropsy samples from an anthrax outbreak in 1979 revealed a novel missense mutation and five unique nucleotide changes among ten victims. The authors concluded that these data indicate little or no horizontal transfer between different B. anthracis strains.

On what basis did the authors conclude that evidence of horizontal transfer is absent from their data?

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Textbook Question

The genetic difference between two Drosophila species, D. heteroneura and D. silvestris, as measured by nucleotide diversity, is about 1.8 percent. The difference between chimpanzees (Pan troglodytes) and humans (H. sapiens) is about the same, yet the latter species is classified in a different genera. In your opinion, is this valid? Explain why.

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Textbook Question

The use of nucleotide sequence data to measure genetic variability is complicated by the fact that the genes of many eukaryotes are complex in organization and contain 5' and 3' flanking regions as well as introns. Researchers have compared the nucleotide sequence of two cloned alleles of the γ-globin gene from a single individual and found a variation of 1 percent. Those differences include 13 substitutions of one nucleotide for another and three short DNA segments that have been inserted in one allele or deleted in the other. None of the changes takes place in the gene's exons (coding regions). Why do you think this is so, and should it change our concept of genetic variation?

469
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Textbook Question

Consider rare disorders in a population caused by an autosomal recessive mutation. From the frequencies of the disorder in the population given, calculate the percentage of heterozygous carriers:

0.000081

429
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Textbook Question

Consider rare disorders in a population caused by an autosomal recessive mutation. From the frequencies of the disorder in the population given, calculate the percentage of heterozygous carriers:

0.09

466
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Textbook Question

Consider rare disorders in a population caused by an autosomal recessive mutation. From the frequencies of the disorder in the population given, calculate the percentage of heterozygous carriers:

0.01

543
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