Q: Given a population of 200 individuals with the following genotype counts at a locus with two alleles (B and b): BB = 98, Bb = 84, bb = 18. What is the frequency of the b allele ($$q) in $$this population?

$$q = \frac{84 + 2 \times 18}{2 \times 200} = \frac{84 + 36}{400} = \frac{120}{400} = 0.30$$

Q: If the frequency of allele $$A$$ ($$p) in a $$population is 0.8, what is the expected frequency of heterozygotes ($$Aa) $$under Hardy–Weinberg equilibrium?

$$2pq = 2 \times 0.8 \times 0.2 = 0.32$$

Q: A population of 100 individuals has the following genotype counts at a locus with two alleles: $$MM = 36$$, $$MN = 48$$, $$NN = 16. $$What is the expected number of $$MN$$ heterozygotes under Hardy–Weinberg equilibrium?

First, $$p = (2 \times 36 + 48)/(2 \times 100) = (72 + 48)/200 = 120/200 = 0.6$$, $$q = 0.4. $$Expected $$MN = 2pq \times 100 = 2 \times 0.6 \times 0.4 \times 100 = 48$$

Question 1

Which of the following best describes the main significance of Hardy–Weinberg equilibrium in population genetics?

Accepted Answer

It provides a mathematical baseline to detect evolutionary changes by showing expected genotype frequencies when no evolution is occurring.

Question 2

Given a population of 200 individuals with the following genotype counts at a locus with two alleles (B and b): BB = 98, Bb = 84, bb = 18. What is the frequency of the b allele ($$q) in $$this population?

Accepted Answer

$$q = \frac{84 + 2 	imes 18}{2 	imes 200} = \frac{84 + 36}{400} = \frac{120}{400} = 0.30$$

Question 3

If the frequency of allele $$A$$ ($$p) in a $$population is 0.8, what is the expected frequency of heterozygotes ($$Aa) $$under Hardy–Weinberg equilibrium?

Accepted Answer

$$2pq = 2 	imes 0.8 	imes 0.2 = 0.32$$

Question 4

A researcher samples a population and finds the following genotype frequencies for a gene with two alleles: $$AA = 0.25$$, $$Aa = 0.50$$, $$aa = 0.25. $$What are the allele frequencies $$p$$ and $$q$$?

Accepted Answer

$$p = 0.25 + 0.50/2 = 0.25 + 0.25 = 0.50$$, $$q = 0.25 + 0.50/2 = 0.25 + 0.25 = 0.50$$

Question 5

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

Accepted Answer

There is strong natural selection favoring one genotype.

Question 6

In a population, the frequency of a recessive phenotype (tt) for a dominant/recessive trait is 0.09. Assuming Hardy–Weinberg equilibrium, what is the frequency of the dominant allele ($$T$$)?

Accepted Answer

$$q^2 = 0.09$$ \Rightarrow q = \sqrt{0.09} = 0.3$$, so p = 1 - 0.3 = 0.7$

Question 7

Which evolutionary force is most likely responsible for a significant change in allele frequencies in a small, isolated population over a few generations?

Accepted Answer

Genetic drift

Question 8

A population of 100 individuals has the following genotype counts at a locus with two alleles: $$MM = 36$$, $$MN = 48$$, $$NN = 16. $$What is the expected number of $$MN$$ heterozygotes under Hardy–Weinberg equilibrium?

Accepted Answer

First, $$p = (2 	imes 36 + 48)/(2 	imes 100) = (72 + 48)/200 = 120/200 = 0.6$$, $$q = 0.4. $$Expected $$MN = 2pq 	imes 100 = 2 	imes 0.6 	imes 0.4 	imes 100 = 48$$

Question 9

Which of the following scenarios would violate the assumption of random mating in Hardy–Weinberg equilibrium?

Accepted Answer

Individuals preferentially mate with others of similar genotype (positive assortative mating).

Question 10

In a population, the observed genotype numbers for a gene with two alleles are: $$AA = 90$$, $$Aa = 41$$, $$aa = 19 ($$total $$N = 150). $$Calculate the allele frequencies $$p$$ and $$q$$ using the genotype frequency method.

Accepted Answer

$$p = f_{AA} + \frac{f_{Aa}}{2} = 0.6 + 0.1367 = 0.7367$$; $$q = f_{aa} + \frac{f_{Aa}}{2} = 0.1267 + 0.1367 = 0.2634$$

Question 11

Which of the following best explains why dominant alleles do not necessarily become more common in a population over time?

Accepted Answer

Dominance does not affect allele frequency changes under Hardy–Weinberg equilibrium; allele frequencies remain constant unless evolutionary forces act.

Question 12

A locus has three alleles: $$A$$, $$B$$, and $$C$$ with frequencies $$p = 0.5$$, $$q = 0.3$$, $$r = 0.2. $$What is the expected frequency of genotype $$AB$$ under Hardy–Weinberg equilibrium?

Accepted Answer

$$2pq = 2 	imes 0.5 	imes 0.3 = 0.3$$

Question 13

Which of the following is TRUE regarding the effect of inbreeding on genotype and allele frequencies?

Accepted Answer

Inbreeding increases the proportion of homozygotes but does not change allele frequencies.

Question 14

A population is found to have observed genotype numbers that differ significantly from those expected under Hardy–Weinberg equilibrium. Which of the following is the most appropriate statistical test to evaluate this difference?

Accepted Answer

Chi-square test ($$\$$chi^2$$ test)

Question 15

In a population, the frequency of allele $$a is 0.1. $$What is the expected proportion of individuals who are carriers (heterozygotes) for a recessive genetic disease under Hardy–Weinberg equilibrium?

Accepted Answer

$$2pq = 2 	imes 0.9 	imes 0.1 = 0.18$$

Question 16

Which of the following best describes linkage disequilibrium?

Accepted Answer

A nonrandom association of alleles at two or more loci, such that some haplotypes occur more or less frequently than expected by chance.

Question 17

For an X-linked gene with two alleles, $$A$$ and $$a$$, with frequencies $$p$$ and $$q$$, what is the expected frequency of males with genotype $$a$$ under Hardy–Weinberg equilibrium?

Accepted Answer

$$q$$

Question 18

Which of the following evolutionary forces is most likely to increase genetic similarity between two previously isolated populations?

Accepted Answer

Gene flow

Question 19

A population is not initially at Hardy–Weinberg equilibrium. If all assumptions of the equilibrium are met, how many generations will it take to reach equilibrium?

Accepted Answer

One generation

Hardy–Weinberg Equilibrium: Principles, Calculations, and Applications

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