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Ch. 23 - Evolutionary Processes
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook
All textbooksFreeman 8th EditionCh. 23 - Evolutionary ProcessesProblem 5
Chapter 23, Problem 5

In a population of 2500, how many babies would you expect to have cystic fibrosis, a homozygous recessive condition, if the frequency of the dominant allele is 0.9 and the population is at Hardy–Weinberg equilibrium?
a. 0.9 × 2500 = 2250
b. 2 × 0.9 × 0.1 × 2500 = 450
c. 0.9 × 0.1 × 2500 = 225
d. 0.1 x 0.1 x 2500 = 25

Verified step by step guidance
1
Understand that cystic fibrosis is a homozygous recessive condition, which means individuals with the condition have two recessive alleles (cc).
Recall the Hardy-Weinberg principle, which states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences.
Identify the frequency of the recessive allele (c) using the given frequency of the dominant allele (C). If the frequency of the dominant allele (C) is 0.9, then the frequency of the recessive allele (c) is 1 - 0.9 = 0.1.
Calculate the expected frequency of individuals with cystic fibrosis (cc) using the formula for homozygous recessive genotype frequency: \( q^2 \), where \( q \) is the frequency of the recessive allele. Thus, \( q^2 = 0.1^2 \).
Multiply the frequency of the homozygous recessive genotype (\( q^2 \)) by the total population size to find the expected number of individuals with cystic fibrosis: \( 0.1^2 \times 2500 \).

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Key Concepts

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

Hardy-Weinberg Equilibrium

The Hardy-Weinberg equilibrium is a principle that describes a stable genetic state in a population where allele and genotype frequencies remain constant across generations, provided no evolutionary influences occur. It assumes random mating, no mutation, migration, or selection, and large population size. This model helps predict genotype frequencies using allele frequencies.
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Testing if a Population is in Hardy-Weinberg Equilibrium

Allele Frequency

Allele frequency refers to how often an allele appears in a population's gene pool. It is expressed as a proportion or percentage of the total alleles for a particular gene. In the context of Hardy-Weinberg equilibrium, allele frequencies are used to calculate expected genotype frequencies, such as homozygous recessive conditions like cystic fibrosis.
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Allele Frequencies

Homozygous Recessive Condition

A homozygous recessive condition occurs when an individual has two copies of a recessive allele, resulting in the expression of a recessive trait or disorder. For cystic fibrosis, individuals must inherit two recessive alleles (cc) to exhibit the condition. Calculating the frequency of such individuals involves squaring the frequency of the recessive allele under Hardy-Weinberg equilibrium.
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Guided course
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Dominant vs. Recessive Alleles
Related Practice
Textbook Question

Why isn't inbreeding considered an evolutionary process?

a. It does not change genotype frequencies.

b. It does not change allele frequencies.

c. It does not occur often enough to be important in evolution.

d. It does not violate the assumptions of the Hardy–Weinberg principle.

Textbook Question

Why is genetic drift aptly named? Select True or False for each statement.

T/F It causes allele frequencies to drift up or down randomly.

T/F It occurs when alleles from one population drift into another.

T/F It occurs when mutations drift into a genome.

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Textbook Question

True or false? Gene flow can either increase or decrease the average fitness of a population. Explain.

Textbook Question

In the 1700s and 1800s, royalty in Europe often married their close relatives; furthermore, recessive genetic diseases such as hemophilia showed up much more often among royals than in the general population. Explain the likely connection.

Textbook Question

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.