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1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
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49. Animal Behavior28m
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51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

22. Evolution of Populations

The Hardy-Weinberg Principle

General Biology

22. Evolution of Populations

The Hardy-Weinberg Principle

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1:17 minutes

Problem 7

Textbook Question

In a population with two alleles, B and b, the allele frequency of b is 0.4. B is dominant to b. What is the frequency of individuals with the dominant phenotype if the population is in Hardy-Weinberg equilibrium?
a. 0.16
b. 0.36
c. 0.48
d. 0.84

Verified step by step guidance

Step 1: Recall the Hardy-Weinberg equilibrium principle, which states that the sum of allele frequencies in a population is 1. Let p represent the frequency of the dominant allele (B) and q represent the frequency of the recessive allele (b). Since the frequency of b (q) is given as 0.4, calculate p using the equation p + q = 1. Solve for p: p = 1 - q.

Step 2: Use the Hardy-Weinberg equation to calculate genotype frequencies. The equation is: \( p^2 + 2pq + q^2 = 1 \), where \( p^2 \) represents the frequency of homozygous dominant individuals (BB), \( 2pq \) represents the frequency of heterozygous individuals (Bb), and \( q^2 \) represents the frequency of homozygous recessive individuals (bb).

Step 3: Calculate \( p^2 \), the frequency of homozygous dominant individuals, by squaring the value of p obtained in Step 1: \( p^2 = p \times p \).

Step 4: Calculate \( 2pq \), the frequency of heterozygous individuals, by multiplying 2, p, and q: \( 2pq = 2 \times p \times q \).

Step 5: Add the frequencies of homozygous dominant (\( p^2 \)) and heterozygous (\( 2pq \)) individuals to determine the total frequency of individuals with the dominant phenotype. This is because both BB and Bb individuals express the dominant phenotype. The final expression is: \( p^2 + 2pq \).

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Key Concepts

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

Hardy-Weinberg Equilibrium

Hardy-Weinberg equilibrium is a principle that describes a population that is not evolving. It states that allele and genotype frequencies will remain constant from generation to generation in the absence of evolutionary influences. For a population to be in Hardy-Weinberg equilibrium, certain conditions must be met, including no mutations, random mating, no natural selection, large population size, and no gene flow.

Allele Frequency

Allele frequency refers to how often a particular allele appears in a population compared to other alleles for the same gene. In this case, the frequency of allele b is given as 0.4, which means that 40% of the alleles in the population are b. The frequency of the dominant allele B can be calculated as 1 - frequency of b, which is 0.6.

Phenotype Frequency

Phenotype frequency is the proportion of individuals in a population that exhibit a particular phenotype, which is the observable trait resulting from the genotype. In this scenario, since B is dominant over b, both BB and Bb genotypes will display the dominant phenotype. The frequency of individuals with the dominant phenotype can be calculated using the Hardy-Weinberg formula, which incorporates the allele frequencies.

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Textbook Question

There are 25 individuals in population 1, all with genotype AA, and there are 40 individuals in population 2, all with genotype aa. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation most likely resulted from

a. Genetic drift.

b. Gene flow.

c. Nonrandom mating.

d. Directional selection.

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A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?

a. 0.7

b. 0.49

c. 0.42

d. 0.21

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Textbook Question

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

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