Ch. 23 - Evolutionary Processes

Freeman - Biological Science 8th Edition

Freeman8th EditionBiological ScienceISBN: 9780138276263당신이 사용하는 게 아니라요?교과서 변경

Freeman 8th Edition

Ch. 23 - Evolutionary Processes

문제 10

23장, 문제 10

In humans, albinism is caused by loss-of-function mutations in genes involved in the synthesis of melanin, the dark pigment in skin. Only people homozygous for a loss-of-function allele (genotype 𝑎𝑎) have albinism. In one study of an American population, individuals with albinism were present at a frequency of about 1 in 10,000 (or 0.0001). Assuming that genotypes are in Hardy–Weinberg Equilibrium, what is the predicted frequency of individuals who are carriers (that is, 𝐴𝑎) for the albinism allele?

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Identify the frequency of the homozygous recessive genotype (aa) in the population, which is given as 0.0001.

Use the Hardy-Weinberg principle, which states that the frequency of the alleles in the population can be represented as p^2 + 2pq + q^2 = 1, where p is the frequency of the dominant allele (A) and q is the frequency of the recessive allele (a).

Calculate the frequency of the recessive allele (q) by taking the square root of the frequency of the homozygous recessive genotype (q^2). Thus, q = sqrt(0.0001).

Determine the frequency of the dominant allele (p) using the relationship p + q = 1.

Calculate the frequency of the heterozygous genotype (Aa) using the formula 2pq.

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Albinism and Genetic Mutations

Albinism is a genetic condition caused by mutations in genes responsible for melanin production, leading to a lack of pigment in skin, hair, and eyes. These mutations are typically loss-of-function, meaning they disrupt the normal function of the gene, resulting in the absence of melanin. Individuals with albinism are homozygous for the recessive allele (aa), while carriers possess one normal allele and one mutated allele (Aa).

Hardy-Weinberg Equilibrium

The Hardy-Weinberg Equilibrium is a principle in population genetics that describes the genetic variation in a population under certain ideal conditions. It states that allele and genotype frequencies will remain constant from generation to generation in the absence of evolutionary influences. This model assumes no mutation, migration, selection, or genetic drift, allowing for the calculation of expected frequencies of genotypes based on allele frequencies.

Carrier Frequency Calculation

To find the frequency of carriers (Aa) in a population under Hardy-Weinberg Equilibrium, we use the allele frequencies derived from the observed frequency of the homozygous recessive genotype (aa). If the frequency of aa is 0.0001, the frequency of the recessive allele (q) is the square root of this value. The frequency of carriers (Aa) can then be calculated using the formula 2pq, where p is the frequency of the dominant allele and q is the frequency of the recessive allele.

관련 실천

교과서 질문

Determine what is incorrect in the following statement: Deer mice living on beaches mutated their genes so that they could have white fur color, providing better camouflage to survive on beaches.

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교과서 질문

Draw a small concept map showing how selection, genetic drift, gene flow, and mutation relate to genetic variation.

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교과서 질문

Suppose you were a conservation biologist working to preserve two populations of monkeys. The first population has 5000 individuals, while the second population has 50,000 individuals. Which population do you expect to have higher genetic diversity? Consider which evolutionary process(es) may be different between these populations. Justify your response.

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교과서 질문

Toucans disperse seeds of key forest species such as juçara palms by eating the fruit and defecating the seeds in new locations, sometimes more than a kilometer away. If there are no toucans, is the genetic diversity of palms likely to increase or decrease within forest fragments? Why?

a. Increase (due to increased genetic drift)

b. Decrease (due to decreased gene flow)

c. Decrease (due to decreased mutation rate)

d. Decrease (due to decreased natural selection)

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교과서 질문

Human activities are causing the fragmentation of the Brazilian Atlantic rain forest. One result is that toucans have become extinct or nearly extinct in some of the forest fragments. Does the absence of toucans affect the forest? Toucans can eat fruits with large seeds because their large bills can open wide. Most other birds in the same forest can only eat small seeds. Ecologist Mauro Galetti and his colleagues measured the seed sizes of palms in forest fragments with and without toucans. The graphs show two of the forest populations they studied. What is the take-home message of the data?

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