Chapter 23: Evolution Of Populations

Question 1

What is microevolution?

Answer 1

Microevolution is the change in allele frequencies in a population over generations due to natural selection, genetic drift, gene flow, and mutation.

Question 2

How does evolution occur at the population level?

Answer 2

Evolution occurs at the population level because individuals do not evolve—populations evolve when allele frequencies change over time.

Question 3

What is a gene pool?

Answer 3

A gene pool consists of all the alleles for all genes in a population at any given time.

Question 4

What does it mean for an allele to be fixed in a population?

Answer 4

An allele is fixed if all individuals in a population are homozygous for the same allele, meaning there is no genetic variation at that locus.

Question 5

What are the five conditions required for Hardy-Weinberg equilibrium?

Answer 5

1. No mutations, 2. Random mating, 3. No natural selection, 4. Large population size (no genetic drift), 5. No gene flow (no migration).

Question 6

What does the Hardy-Weinberg equation (p² + 2pq + q² = 1) represent?

Answer 6

It represents the expected genotype frequencies in a non-evolving population, where p² is the frequency of homozygous dominant individuals, 2pq is heterozygous, and q² is homozygous recessive.

Question 7

How does the Hardy-Weinberg principle help scientists?

Answer 7

It provides a null hypothesis to detect whether evolution is occurring by comparing observed vs. expected genotype frequencies.

Question 8

What are the three main sources of genetic variation?

Answer 8

1. Mutations (random changes in DNA), 2. Genetic recombination (from sexual reproduction), 3. Gene flow (migration between populations).

Question 9

How do mutations contribute to evolution?

Answer 9

Mutations introduce new alleles into a population; while most are neutral or harmful, some provide beneficial adaptations.

Question 10

How does sexual reproduction create genetic variation?

Answer 10

It reshuffles alleles through crossing over (during meiosis), independent assortment, and random fertilization.

Question 11

What is genetic drift?

Answer 11

Genetic drift is the random fluctuation of allele frequencies in populations. (Chance)

Question 12

What is the bottleneck effect?

Answer 12

The bottleneck effect occurs when a sudden reduction in population size (e.g., disaster) decreases genetic diversity.

Question 13

What is the founder effect?

Answer 13

The founder effect occurs when a small group of individuals starts a new population, leading to reduced genetic variation and potential fixation of alleles.

Question 14

How does gene flow affect populations?

Answer 14

Gene flow moves alleles between populations, increasing genetic diversity and preventing divergence.

Question 15

What are the three types of natural selection?

Answer 15

1. Directional selection (favors one extreme phenotype), 2. Stabilizing selection (favors intermediate traits), 3. Disruptive selection (favors both extreme phenotypes).

Question 16

How does natural selection differ from genetic drift?

Answer 16

Natural selection is non-random and favors traits that improve fitness, while genetic drift is random and can lead to allele loss.

Question 17

What is balancing selection?

Answer 17

Balancing selection maintains multiple alleles in a population by mechanisms such as frequency-dependent selection and heterozygote advantage.

Question 18

How does heterozygote advantage maintain genetic variation?

Answer 18

Heterozygous individuals have higher fitness than either homozygote, as seen in sickle-cell disease resistance to malaria.

Question 19

What is frequency-dependent selection?

Answer 19

A form of selection where the fitness of a phenotype depends on its frequency in the population (e.g., rare alleles can have an advantage).

Question 20

What is sexual selection?

Answer 20

Sexual selection is a form of natural selection where individuals with certain traits are more likely to attract mates and reproduce.

Question 21

What are the two types of sexual selection?

Answer 21

1. Intrasexual selection (competition among individuals of the same sex, e.g., male-male combat), 2. Intersexual selection (mate choice, e.g., female preference for bright colors).

Question 22

What is the ‘good genes’ hypothesis?

Answer 22

The good genes hypothesis suggests that certain traits in males indicate genetic quality, leading females to prefer those mates.

Question 23

Why doesn’t natural selection create perfect organisms?

Answer 23

1. Selection can only act on existing variation, 2. Evolution is limited by historical constraints, 3. Adaptations involve trade-offs, 4. Chance events affect evolution.

Question 24

What are evolutionary trade-offs?

Answer 24

Trade-offs occur when a beneficial trait comes at a cost, such as bright coloration in males increasing predation risk.

Question 25

What is the neutral theory of molecular evolution?

Answer 25

The neutral theory proposes that most genetic variation is due to neutral mutations that evolve through genetic drift rather than selection.

Question 26

How are molecular clocks used in evolutionary biology?

Answer 26

Molecular clocks estimate evolutionary divergence times by analyzing the accumulation of neutral mutations.

Question 27

How does genetic variation in humans provide evidence for evolution?

Answer 27

Human genetic diversity follows migration patterns, with variations in skin color, disease resistance, and lactose tolerance adapting to different environments.

Question 28

How has natural selection influenced human evolution?

Answer 28

Traits such as sickle-cell resistance, skin pigmentation, and high-altitude adaptations show evidence of selection for survival advantages.

Question 29

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Answer 29

Back

Question 30

What are real-world applications of the Hardy-Weinberg equation?

Answer 30

It is used to estimate allele frequencies in human populations, detect evolutionary changes, and study genetic disorders.

Question 31

How do medical researchers use Hardy-Weinberg equilibrium?

Answer 31

They use it to predict carrier frequencies of genetic diseases, such as sickle-cell anemia and cystic fibrosis, in populations.

Question 32

What is the difference between genotypic and phenotypic variation?

Answer 32

Genotypic variation is due to differences in DNA sequences, while phenotypic variation is the observable expression of those genetic differences.

Question 33

How do environmental factors influence phenotypic variation?

Answer 33

Environmental conditions like temperature, diet, and exposure to stressors can influence gene expression and result in phenotypic plasticity.

Question 34

Why does genetic drift have a stronger effect in small populations?

Answer 34

In small populations, random fluctuations in allele frequencies are more pronounced, leading to fixation or loss of alleles more quickly.

Question 35

Can genetic drift lead to speciation?

Answer 35

Yes, when populations are small and isolated, genetic drift can contribute to reproductive isolation and eventually lead to the formation of new species.

Question 36

How does gene flow counteract the effects of genetic drift?

Answer 36

Gene flow introduces new alleles into a population, increasing genetic diversity and preventing alleles from becoming fixed or lost.

Question 37

Why can gene flow slow adaptation to local environments?

Answer 37

By introducing alleles from other populations, gene flow can dilute locally adapted traits, reducing the efficiency of natural selection.

Question 38

What is artificial selection, and how does it differ from natural selection?

Answer 38

Artificial selection is the human-driven process of breeding organisms for desired traits, whereas natural selection occurs without human intervention.

Question 39

What is an example of frequency-dependent selection?

Answer 39

The scale-eating cichlid fish has left- and right-jawed morphs; their fitness depends on the relative frequency of each type in the population.

Question 40

How does sexual dimorphism evolve?

Answer 40

Sexual dimorphism arises when males and females develop distinct traits due to sexual selection, often for attracting mates or competing for access to mates.

Question 41

What is an example of runaway selection?

Answer 41

The long tail of male peacocks is an example; female preference for longer tails led to exaggerated traits over generations.

Question 42

Why can’t evolution produce ‘perfect’ organisms?

Answer 42

Constraints like genetic history, developmental limitations, and trade-offs prevent organisms from achieving perfect adaptation.

Question 43

What is an example of a historical constraint in evolution?

Answer 43

The human spine evolved from a quadrupedal ancestor, which causes issues like back pain in bipedal humans.

Question 44

What is synonymous vs. nonsynonymous mutation?

Answer 44

A synonymous mutation does not change the amino acid sequence, while a nonsynonymous mutation alters the protein structure and function.

Question 45

What is an example of a conserved gene across species?

Answer 45

The Hox genes, which control body plan development, are conserved across many animals, showing deep evolutionary relationships.

Question 46

How does lactose tolerance provide evidence for natural selection?

Answer 46

Lactose tolerance evolved independently in human populations that domesticated dairy animals, providing a survival advantage.

Question 47

How does the FOXP2 gene relate to human evolution?

Answer 47

FOXP2 is linked to speech and language ability, and mutations in this gene can lead to communication disorders.

Question 48

Front

Answer 48

Back

Question 49

How can you determine if a population is in Hardy-Weinberg equilibrium?

Answer 49

Compare observed genotype frequencies with expected frequencies using the Hardy-Weinberg equation. If they differ significantly (e.g., using a chi-square test), evolution is occurring.

Question 50

If q² = 0.01 in a Hardy-Weinberg population, what is the frequency of heterozygotes?

Answer 50

q² = 0.01 means q = 0.1. Since 2pq represents heterozygotes, p = 1 - 0.1 = 0.9. Then, 2pq = 2(0.9)(0.1) = 0.18 or 18%.

Question 51

Why might a population experience both genetic drift and natural selection simultaneously?

Answer 51

In small populations, genetic drift can cause random allele fluctuations, but if one allele provides a selective advantage, natural selection can still act on it.

Question 52

How does inbreeding affect evolution?

Answer 52

Inbreeding increases homozygosity, reducing genetic diversity and increasing the risk of harmful recessive alleles becoming more frequent.

Question 53

What is industrial melanism, and how does it demonstrate natural selection?

Answer 53

Industrial melanism is seen in the peppered moth, where darker moths became more common in polluted environments due to better camouflage, demonstrating directional selection.

Question 54

Why do island species often exhibit rapid speciation?

Answer 54

Small, isolated populations on islands experience genetic drift, founder effects, and different selective pressures, leading to adaptive radiation (e.g., Darwin’s finches).

Question 55

Does evolution always lead to more complex organisms?

Answer 55

No. Evolution is not goal-oriented. Simpler organisms like bacteria can be just as successful as more complex ones if they are well-adapted.

Question 56

Why does genetic variation persist despite natural selection?

Answer 56

Balancing selection, heterozygote advantage, frequency-dependent selection, and diploidy all help maintain genetic diversity.

Question 57

How do chromosomal mutations impact evolution?

Answer 57

Larger chromosomal mutations (duplications, deletions, translocations) can create new gene functions, increase genetic material, or cause reproductive isolation.

Question 58

What is an example of a beneficial mutation in humans?

Answer 58

The CCR5-Δ32 mutation provides resistance to HIV infection by preventing the virus from binding to white blood cells.

Question 59

How can gene flow introduce new evolutionary advantages?

Answer 59

When populations mix, advantageous alleles from one group may spread and improve adaptation in the recipient population (e.g., resistance to malaria in Africa due to migration).

Question 60

What is an example of stabilizing selection in humans?

Answer 60

Human birth weight: Extremely low or high birth weights have higher infant mortality, so intermediate weights are favored.

Question 61

How does sexual selection lead to exaggerated traits?

Answer 61

Traits like peacock tails evolve because they increase reproductive success, even if they reduce survival, leading to a trade-off.

Question 62

What is an example of sexual selection affecting survival?

Answer 62

In elephant seals, males fight for access to females; larger males win more fights and pass on their genes, even though size increases energy needs and predation risk.

Question 63

What are evolutionary constraints, and how do they limit adaptation?

Answer 63

Historical constraints (body plan limitations), genetic correlations (pleiotropy), and trade-offs prevent organisms from evolving 'perfect' solutions.

Question 64

Why do vestigial structures exist?

Answer 64

Vestigial structures are remnants of ancestral traits that have lost their original function due to evolutionary changes (e.g., human tailbone, whale pelvis).