Q: A population of 500 wildflowers has two alleles for flower color: R (red) and r (white). If 320 plants are RR, 160 are Rr, and 20 are rr, what is the frequency of the r allele in the population?

$$\frac{160 + 2 \times 20}{1000} = \frac{200}{1000} = 0.2$$

Q: In a population at Hardy-Weinberg equilibrium, the frequency of the recessive allele $$q is 0.3. $$What is the expected frequency of heterozygotes?

$$2pq = 2 \times 0.7 \times 0.3 = 0.42$$

Q: A population of 1000 individuals has genotype frequencies for a gene as follows: 490 AA, 420 Aa, and 90 aa. What is the frequency of the a allele?

$$q = \frac{2 \times 90 + 420}{2 \times 1000} = \frac{180 + 420}{2000} = \frac{600}{2000} = 0.3$$

Question 1

Which of the following best explains why genetic variation is essential for evolution within a population?

Accepted Answer

It provides the raw material upon which evolutionary mechanisms such as natural selection, genetic drift, and gene flow can act.

Question 2

A population of 500 wildflowers has two alleles for flower color: R (red) and r (white). If 320 plants are RR, 160 are Rr, and 20 are rr, what is the frequency of the r allele in the population?

Accepted Answer

$$\frac{160 + 2 	imes 20}{1000} = \frac{200}{1000} = 0.2$$

Question 3

Which of the following scenarios best illustrates the founder effect?

Accepted Answer

A small group of beetles migrates to a new island, and their descendants have different allele frequencies than the original population.

Question 4

In a population at Hardy-Weinberg equilibrium, the frequency of the recessive allele $$q is 0.3. $$What is the expected frequency of heterozygotes?

Accepted Answer

$$2pq = 2 	imes 0.7 	imes 0.3 = 0.42$$

Question 5

Which of the following is a direct consequence of genetic drift in a small population?

Accepted Answer

A random loss or fixation of alleles, potentially reducing genetic variation.

Question 6

A population of mice has a dominant allele $$B ($$black coat) and a recessive allele $$b ($$brown coat). If the frequency of $$bb$$ individuals is 0.09, what is the frequency of the $$B$$ allele assuming Hardy-Weinberg equilibrium?

Accepted Answer

$$q = \sqrt{0.09} = 0.3;\ p = 1 - 0.3 = 0.7$$

Question 7

Which of the following best describes balancing selection?

Accepted Answer

It maintains multiple phenotypes in a population, often through mechanisms like frequency-dependent selection or heterozygote advantage.

Question 8

In the case of sickle-cell disease, why does the sickle-cell allele remain at high frequency in certain human populations?

Accepted Answer

Heterozygotes have a survival advantage in regions where malaria is prevalent, a phenomenon known as heterozygote advantage.

Question 9

Which of the following is NOT an assumption of the Hardy-Weinberg equilibrium?

Accepted Answer

Natural selection favors the most advantageous genotype.

Question 10

A population of 1000 individuals has genotype frequencies for a gene as follows: 490 AA, 420 Aa, and 90 aa. What is the frequency of the a allele?

Accepted Answer

$$q = \frac{2 	imes 90 + 420}{2 	imes 1000} = \frac{180 + 420}{2000} = \frac{600}{2000} = 0.3$$

Question 11

Which of the following best explains why natural selection is the only evolutionary mechanism that consistently leads to adaptive evolution?

Accepted Answer

It increases the frequency of alleles that improve survival and reproduction in a given environment.

Question 12

Which of the following is an example of disruptive selection?

Accepted Answer

A population of finches where both small and large beak sizes are favored because they are more efficient at eating different types of seeds, while intermediate beak sizes are less efficient.

Question 13

A scientist observes that after a severe drought, the average beak depth in a population of finches increases. Which mechanism best explains this evolutionary change?

Accepted Answer

Natural selection favoring individuals with deeper beaks who could eat the available seeds.

Question 14

Which of the following statements about gene flow is correct?

Accepted Answer

Gene flow can introduce new alleles into a population, reducing genetic differences between populations.

Question 15

In a population of soybeans, the frequency of allele $$G is 0.45. $$What is the expected frequency of $$gg$$ homozygotes under Hardy-Weinberg equilibrium?

Accepted Answer

$$q = 1 - 0.45 = 0.55;\ q^2$ = 0.55^2$ = 0.3025$$

Question 16

Which of the following is an example of frequency-dependent selection?

Accepted Answer

In a fish species, left-mouthed and right-mouthed individuals alternate in frequency because prey guard against the more common phenotype, giving a fitness advantage to the rarer type.

Question 17

Which of the following best describes the effect of a frameshift mutation?

Accepted Answer

It changes the reading frame of the gene, altering all subsequent amino acids and likely resulting in a nonfunctional protein.

Question 18

Which of the following is a reason why natural selection cannot produce perfect organisms?

Accepted Answer

Natural selection can only act on existing variations, and evolution is limited by historical constraints and trade-offs.

Question 19

A population of frogs is isolated on an island. Over time, random events cause certain alleles to become fixed while others are lost, reducing genetic variation. Which evolutionary mechanism is primarily responsible for this outcome?

Accepted Answer

Genetic drift

Evolution of Populations: Mechanisms and Genetic Variation (Chapter 23 Study Notes)

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