genetics 22: population genetics

Which of the following best describes the significance of gene mutations in evolution?
A. All gene mutations are harmful and are removed by natural selection
B. Gene mutations are random but always beneficial
C. Gene mutations provide raw material for evolutionary change
D. Gene mutations do not affect evolutionary processes

Gene mutations provide raw material for evolutionary change

T/F: Molecular evolution focuses exclusively on morphological traits and their changes through time.

false

n an evolutionary tree, what does each branching point (node) most accurately represent?
A. A mass extinction event
B. The appearance of a morphological trait
C. A genetic divergence due to mutation(s)
D. The end of a lineage

A genetic divergence due to mutation(s)

T/F: Each individual's genome (except in identical twins) is unique due to accumulated genetic variation.

true

T/F: Speciation always requires a large number of genetic differences between populations.

false

T/F: Two individuals of the same species can have differences in their DNA without being different species.

true

Which of the following best explains why gene trees and species trees may differ?
A. All genes mutate at the same rate
B. Natural selection prevents genetic differences
C. Genes can evolve independently of the species they reside in
D. Species always inherit identical gene trees

Genes can evolve independently of the species they reside in

What does it mean when an allele becomes "fixed" in a population?
A. It mutates into a different form
B. It is shared with another species
C. It is present in some, but not all, individuals
D. It is the only allele present in the population

It is the only allele present in the population

How can recombination affect gene trees?
A. It prevents new alleles from forming
B. It leads to uniform gene histories across species
C. It creates different evolutionary histories within the same gene
D. It eliminates allele loss

It creates different evolutionary histories within the same gene

When an allele is completely gone from a population, it is said to be ________

lost

Why is comparing multiple genes better than using just one when constructing a species tree?
A. One gene always contains all evolutionary information
B. It ensures only fixed alleles are used
C. It reduces random variation and gives a more accurate view of species relationships
D. It avoids the need for DNA sequencing

It reduces random variation and gives a more accurate view of species relationships

What is the benefit of analyzing several genetic loci across species?
A. It increases the chance of sampling the same mutation
B. It helps identify random mutations only
C. It helps identify key mutations that reflect evolutionary history
D. It eliminates the need for comparing alleles

It helps identify key mutations that reflect evolutionary history

Why is studying multiple alleles of a gene useful in evolutionary research?
A. It increases gene loss rates
B. It amplifies random mutation effects
C. It smooths out randomness from fixation or loss of alleles
D. It ensures all individuals are genetically identical

It smooths out randomness from fixation or loss of alleles

True or False: Examining multiple loci across species helps differentiate true species differences from random gene variation.

true

True or False: Using multiple alleles and genes in studies helps reduce errors caused by gene fixation or loss in small samples.

true

Why do some proteins evolve more slowly than others?
A. They are not part of the genome
B. They are less exposed to mutations
C. They are essential to life and changes may be harmful
D. They have fewer amino acids

They are essential to life and changes may be harmful

What characterizes a synonymous substitution?
A. It changes the amino acid sequence of a protein
B. It always causes harmful effects
C. It does not change the amino acid made by a codon
D. It is removed by natural selection immediately

It does not change the amino acid made by a codon

Which of the following is true about nonsynonymous substitutions?
A. They are more frequent than synonymous ones
B. They do not affect protein structure
C. They are more likely to affect the phenotype
D. They are ignored by natural selection

They are more likely to affect the phenotype

Synonymous substitutions usually accumulate faster over time because they are not typically removed by __________ __________.

natural selection

Nonsynonymous substitutions change the __________ sequence of a protein and can impact its function.

amino acid

Genes with essential functions tend to evolve more __________ than others due to the potential negative effects of mutations.

slowly

True or False: Nonsynonymous substitutions can be beneficial, harmful, or neutral depending on their impact on protein function.

true

True or False: The rate of substitution is generally lower for nonsynonymous mutations because many are removed by natural selection.

true

True or False: The rate of substitution is generally lower for synonymous mutations because many are removed by natural selection.

false (rate of substitution is high)

What is a paralog?
A. A gene in a different species that has the same function
B. A non-functional piece of DNA
C. One of two gene copies resulting from duplication within the same genome
D. A gene inherited from an ancient ancestor

One of two gene copies resulting from duplication within the same genome

What is one evolutionary advantage of gene duplication?
A. It reduces genetic diversity
B. It eliminates harmful alleles
C. It creates opportunities for new gene functions to evolve
D. It ensures only one copy of each gene is expressed

It creates opportunities for new gene functions to evolve

What happens when a duplicated gene becomes a pseudogene?
A. It produces more proteins than usual
B. It codes for a protein with a new function
C. It is silenced by the immune system
D. It accumulates mutations and loses its function

It accumulates mutations and loses its function

One possible outcome of gene duplication is that a paralog evolves a new function or a new __________ pattern.

expression

True or False: Gene duplication can result in one gene being non-functional while the other maintains or changes its function.

true

What advantage does gene duplication provide to organisms?
A. It removes all harmful mutations
B. It allows new gene functions to evolve while keeping the original gene intact
C. It reduces genetic diversity in populations
D. It prevents any mutations from occurring

It allows new gene functions to evolve while keeping the original gene intact

What is population genetics primarily concerned with?
A. The study of single individuals only
B. Applying genetic principles to groups of organisms in populations
C. Studying genes outside populations
D. Preventing gene flow between species

Applying genetic principles to groups of organisms in populations

Which best describes a subpopulation?
A. A group of individuals from different species
B. A small group within a population that breeds mostly among themselves
C. An isolated species
D. A population with unlimited migration between groups

A small group within a population that breeds mostly among themselves

__________ is the movement or breeding between subpopulations within a species.

migration

A __________ population is a smaller breeding group within a larger population where most breeding occurs inside that group.

local

True or False: Genetic diversity in populations can increase because gene duplication allows exploration of new gene functions.

true

What does the gene pool of a population represent?
A. The genes of a single individual
B. All genetic information (alleles) in every individual of a population
C. Only the dominant alleles in a population
D. Genes shared between different species

All genetic information (alleles) in every individual of a population

Genotype frequency refers to:
A. The number of alleles in a population
B. The proportion of individuals with a specific genotype (e.g., AA, Aa, aa)
C. The mutation rate of a gene
D. The frequency of gene duplication events

The proportion of individuals with a specific genotype (e.g., AA, Aa, aa)

Allele frequency is:
A. The proportion of individuals with a specific genotype
B. How common a specific allele is in the gene pool
C. The total number of genes in the population
D. The number of genotypes in a population

How common a specific allele is in the gene pool

Allele frequencies are estimated using __________ frequencies.

genotype

True or False: Allele frequency is based on how many copies of an allele exist compared to all gene copies in the population.

true

True or False: Genotype frequency refers to the proportion of different alleles present in the population.

false

To calculate allele frequencies, you multiply the number of individuals with genotype AA by _____ to find the total A alleles from AA.

2

According to Hardy-Weinberg principles, if a population is not evolving, the allele frequencies in gametes will be:
A. Different from those in reproducing adults
B. The same as those in reproducing adults
C. Always equal to 0.5
D. Determined only by the dominant allele

The same as those in reproducing adults

In population genetics Punnett squares, what is different compared to classic Mendelian Punnett squares?
A. They use genotype frequencies of parents only
B. They assume alleles are equally common in the population
C. They use population-wide allele frequencies and account for unequal allele frequencies
D. They ignore allele frequencies

They use population-wide allele frequencies and account for unequal allele frequencies

If p is the frequency of allele A, and q is the frequency of allele a, which equation always holds true?
A. p × q = 1
B. p + q = 1
C. p – q = 0
D. p + q = 0

p + q = 1

In a non-evolving population, gametes unite at random with no __________ or bias.

selection

A population genetics Punnett square uses __________ allele frequencies rather than just the genotypes of two parents.

population-wide

True or False: In population genetics, allele frequencies are assumed to be equally distributed in males and females.

true

According to Hardy-Weinberg equilibrium, the expected frequency of heterozygous genotype Aa is:
A. p²
B. q²
C. 2pq
D. p + q

2pq

If allele a is rare in the population (q is small), which genotype will most commonly carry the rare allele?
A. aa
B. AA
C. Aa
D. None

Aa

Why is a recessive rare allele often "invisible" in a population?
A. Because heterozygotes show the recessive trait
B. Because homozygous recessive individuals (aa) are very rare (q² is small)
C. Because dominant alleles hide all recessive alleles
D. Because recessive alleles do not exist in the population

Because homozygous recessive individuals (aa) are very rare (q² is small)

he Hardy-Weinberg equation for genotype frequencies is __________ for AA, 2pq for Aa, and __________ for aa.

p², q²

When allele q is rare, the frequency of homozygous recessive individuals (aa) is approximately __________.

q² (very small)

True or False: The frequency of heterozygous individuals (Aa) remains relatively high even when the allele a is rare.

true

True or False: A rare recessive allele’s effects are usually hidden in heterozygous individuals.

true

Which of the following is NOT a condition required for a population to be in Hardy-Weinberg equilibrium?
A. No mutation
B. Large population size
C. Random mating
D. High migration rates

High migration rates

If a population is in Hardy-Weinberg equilibrium, what can be said about allele frequencies over time?
A. They fluctuate randomly every generation
B. They change only due to natural selection
C. They remain constant across generations
D. They increase with each generation

They remain constant across generations

If the allele frequencies in a population are p = 0.6 and q = 0.4, what is the expected frequency of heterozygotes (A1A2)?
A. 0.16
B. 0.24
C. 0.48
D. 1.00

0.48

In Hardy-Weinberg equilibrium, the sum of all allele frequencies in a population is __________.

1

The formula for calculating the expected frequency of homozygous dominant individuals (A1A1) in a population is __________.

p²

If allele frequencies change due to mutation or selection, the population will shift to a new __________.

Hardy-Weinberg equilibrium

True or False: Populations in Hardy-Weinberg equilibrium reach expected genotype frequencies after several generations.

False (they reach equilibrium in just one generation)

True or False: The Hardy-Weinberg principle assumes that individuals mate randomly.

true

Which of the following is a key reason large populations are important for Hardy-Weinberg equilibrium?
A. They allow more mutations to happen
B. They prevent genetic drift from causing big random changes in allele frequencies
C. They encourage non-random mating
D. They increase migration

They prevent genetic drift from causing big random changes in allele frequencies

Non-random mating violates Hardy-Weinberg assumptions because:
A. It causes mutations
B. Individuals choose mates based on traits or relatedness, affecting genotype frequencies
C. It increases gene flow
D. It leads to equal survival of all genotypes

. Individuals choose mates based on traits or relatedness, affecting genotype frequencies

Which factor introduces new alleles into the gene pool, violating Hardy-Weinberg assumptions?
A. Genetic drift
B. Migration
C. Mutation
D. Random mating

Mutation

Genetic __________ is the random change in allele frequencies due to chance events, especially in small populations.

drift

One limitation of the Hardy-Weinberg model is that its assumptions __________ in real populations.

rarely exist

True or False: Natural selection is assumed to be absent in an ideal Hardy-Weinberg population.

true

True or False: Gene flow (migration) can cause allele frequencies to change and violates Hardy-Weinberg assumptions.

true

f a gene has three alleles A₁, A₂, and A₃ with frequencies p₁, p₂, and p₃, what is the sum of these allele frequencies?
A. p₁ × p₂ × p₃
B. 1
C. p₁ + p₂
D. p₁ + p₂ + p₃ + 1

1

Which of the following genotype frequency formulas is correct for a heterozygous genotype involving alleles A₁ and A₂?
A. p₁²
B. 2 × p₁ × p₂
C. p₂²
D. p₁ + p₂

2 × p₁ × p₂

Why is the ABO blood group system a good example for studying Hardy-Weinberg equilibrium with multiple alleles?
A. It only has two alleles
B. The alleles are codominant and multiple alleles exist in the population
C. It does not follow Hardy-Weinberg principles
D. It evolves rapidly

The alleles are codominant and multiple alleles exist in the population

How many genotypes are possible for the ABO blood group gene with three alleles Iᴬ, Iᴮ, and i?
A. 3
B. 4
C. 5
D. 6

6

Which genotype corresponds to blood type AB?
A. IᴬIᴬ or Iᴬi
B. IᴮIᴮ or Iᴮi
C. IᴬIᴮ
D. ii

IᴬIᴮ

If p₁, p₂, and p₃ represent the frequencies of Iᴬ, Iᴮ, and i respectively, which of the following represents the frequency of genotype Iᴬi?
A. p₁²
B. 2 × p₁ × p₃
C. p₃²
D. 2 × p₂ × p₃

2 × p₁ × p₃

The frequency of genotype ii (blood type O) is calculated as __________.

p₃²

Suppose in a population the allele frequencies are:

• p₁ (Iᴬ) = 0.3

• p₂ (Iᴮ) = 0.2

• p₃ (i) = 0.5

Calculate the expected frequency of individuals with blood type A (IᴬIᴬ or Iᴬi) under Hardy-Weinberg equilibrium.

0.39

Why do males express X-linked recessive traits more frequently than females?
A. Males have two X chromosomes
B. Males have only one X chromosome, so one recessive allele causes the trait
C. Females have only one X chromosome
D. Females do not carry X-linked alleles

Males have only one X chromosome, so one recessive allele causes the trait

In an X-linked gene with alleles A (dominant) and a (recessive), if q is the frequency of allele a, what is the expected frequency of males expressing the recessive trait?
A. q²
B. 2q
C. q
D. p

q

For females, what genotype frequency corresponds to expressing an X-linked recessive trait?
A. p²
B. 2pq
C. q
D. q²

q²

Males have only __________ copy of the X chromosome, so their genotype frequency equals allele frequency.

one

Females must be __________ (two copies of the recessive allele) to express an X-linked recessive trait.

homozygous recessive / aa / q²

True or False: There are no heterozygous males for X-linked genes because males have only one X chromosome.

true

True or False: The frequency of females expressing an X-linked recessive trait is usually higher than that of males.

false

True or False: X-linked recessive diseases like hemophilia appear more frequently in males than females.

true

If the frequency of the recessive allele a on the X chromosome is q = 0.1, what is the expected frequency of females expressing the recessive trait and the expected frequency of males expressing it?

• Females express recessive trait frequency = q² = 0.1² = 0.01 (1%)

• Males express recessive trait frequency = q = 0.1 (10%)

What is the main genetic consequence of inbreeding on a population?
A. Increase in heterozygous individuals
B. Increase in homozygous individuals
C. Increase in mutation rates
D. Increase in allele diversity

Increase in homozygous individuals

Why does inbreeding lead to fewer heterozygous individuals?
A. Because of random mating
B. Because offspring inherit identical alleles more often from closely related parents
C. Because mutations increase
D. Because alleles are lost through migration

Because offspring inherit identical alleles more often from closely related parents

Which example illustrates extreme inbreeding?
A. Cross-pollination between different plants
B. Self-fertilization in plants
C. Migration of individuals into a population
D. Random mating in large populations

Self-fertilization in plants

Inbreeding increases the frequency of __________ genotypes and decreases the frequency of __________ genotypes.

homozygous; heterozygous

After several rounds of self-fertilization starting from a heterozygous plant (Aa), the proportion of heterozygous offspring becomes __________ than 10%.

less

Inbreeding reduces genetic __________ by increasing homozygosity.

diversity

Suppose a plant population starts with 100% heterozygous (Aa) individuals. After 4 generations of self-fertilization, what percentage of the offspring would still be heterozygous? (Hint: heterozygosity halves each generation of selfing.)

After 1 generation: 50% heterozygous
After 2 generations: 25%
After 3 generations: 12.5%
After 4 generations: 6.25%

Answer: Approximately 6.25%

Why does inbreeding increase the expression of harmful recessive traits in a population?
A. It increases mutation rates
B. It increases heterozygosity
C. It increases the frequency of homozygous recessive individuals
D. It eliminates recessive alleles

It increases the frequency of homozygous recessive individuals

Compared to self-fertilization, mating between cousins leads to:
A. Faster loss of heterozygosity
B. Slower loss of heterozygosity
C. No change in heterozygosity
D. Immediate fixation of recessive alleles

Slower loss of heterozygosity

Why do harmful recessive alleles usually remain “hidden” in populations practicing random mating?
A. They don’t exist in those populations
B. They are mostly present in heterozygous individuals who do not express the trait
C. They mutate frequently
D. They are dominant and always expressed

They are mostly present in heterozygous individuals who do not express the trait

True or False: Self-fertilization and cousin mating cause identical rates of increase in homozygosity.

false

Which of the following is NOT a condition assumed by the Hardy-Weinberg principle?
A. No mutation
B. No natural selection
C. Constant population size
D. Frequent migration

Frequent migration

What is considered the ultimate source of genetic variation in populations?
A. Genetic drift
B. Gene flow
C. Mutation
D. Natural selection

Mutation