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Questions and Answers
Which of the following processes contribute to microevolution?
Which of the following processes contribute to microevolution?
Microevolution requires the presence of genetic variation in a population.
Microevolution requires the presence of genetic variation in a population.
True
What is the relationship between macroevolution and microevolution?
What is the relationship between macroevolution and microevolution?
Macroevolution is the long-term consequence of microevolution.
The processes of microevolution include mutation, gene flow, genetic drift, and __________.
The processes of microevolution include mutation, gene flow, genetic drift, and __________.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Which term describes a population where individuals mate randomly with respect to their genotype?
Which term describes a population where individuals mate randomly with respect to their genotype?
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Non-random mating affects allele frequencies directly.
Non-random mating affects allele frequencies directly.
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What is the term for when relatives mate more often than expected by chance?
What is the term for when relatives mate more often than expected by chance?
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Individuals may self-fertilize more or less often than expected by chance, leading to _____.
Individuals may self-fertilize more or less often than expected by chance, leading to _____.
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Match the following terms with their correct descriptions:
Match the following terms with their correct descriptions:
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What is microevolution primarily focused on?
What is microevolution primarily focused on?
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Macroevolution deals with evolutionary changes over shorter time periods compared to microevolution.
Macroevolution deals with evolutionary changes over shorter time periods compared to microevolution.
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What term describes the decline in fitness due to inbreeding?
What term describes the decline in fitness due to inbreeding?
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Gene flow is the movement of ______ between populations.
Gene flow is the movement of ______ between populations.
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Match the following concepts with their descriptions:
Match the following concepts with their descriptions:
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Which of the following is NOT a factor that can affect allele frequencies?
Which of the following is NOT a factor that can affect allele frequencies?
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Beneficial mutations always increase fitness in a population.
Beneficial mutations always increase fitness in a population.
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What is the primary consequence of a population bottleneck?
What is the primary consequence of a population bottleneck?
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What happens to genetic variation when a population undergoes a bottleneck?
What happens to genetic variation when a population undergoes a bottleneck?
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Higher migration rates lead to more differences in allele frequencies among populations.
Higher migration rates lead to more differences in allele frequencies among populations.
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What does a founder event refer to in population genetics?
What does a founder event refer to in population genetics?
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Population bottlenecks can result in increased frequency of a __________ mutation in an isolated population.
Population bottlenecks can result in increased frequency of a __________ mutation in an isolated population.
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Match the following human health implications with the associated population:
Match the following human health implications with the associated population:
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If the migration rate is set to 0.01, what does this indicate?
If the migration rate is set to 0.01, what does this indicate?
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Bottlenecks can be caused only by environmental factors.
Bottlenecks can be caused only by environmental factors.
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What does the probability of an allele eventually fixing by drift equal?
What does the probability of an allele eventually fixing by drift equal?
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What is the main effect of genetic drift on allele frequencies in finite populations?
What is the main effect of genetic drift on allele frequencies in finite populations?
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Smaller populations experience weaker genetic drift compared to larger populations.
Smaller populations experience weaker genetic drift compared to larger populations.
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How does genetic drift affect heterozygosity in a population?
How does genetic drift affect heterozygosity in a population?
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The __________ effect can cause deleterious alleles to increase in frequency in small populations.
The __________ effect can cause deleterious alleles to increase in frequency in small populations.
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In the absence of gene flow, how will populations behave over time due to genetic drift?
In the absence of gene flow, how will populations behave over time due to genetic drift?
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Drift-induced deviations from Hardy-Weinberg expected genotype frequencies are usually large in larger populations.
Drift-induced deviations from Hardy-Weinberg expected genotype frequencies are usually large in larger populations.
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What happens to allele frequencies when the frequency of an allele gets closer to 0 in a finite population?
What happens to allele frequencies when the frequency of an allele gets closer to 0 in a finite population?
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Which conditions are necessary for natural selection to occur?
Which conditions are necessary for natural selection to occur?
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Natural selection leads to adaptations that increase survival and reproduction in a given environment.
Natural selection leads to adaptations that increase survival and reproduction in a given environment.
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What is the role of genetic drift in evolution?
What is the role of genetic drift in evolution?
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The contribution of an individual to the next generation, measured by the number of offspring produced, is known as _______.
The contribution of an individual to the next generation, measured by the number of offspring produced, is known as _______.
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What must be true for a trait to evolve via natural selection?
What must be true for a trait to evolve via natural selection?
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Genetic drift tends to reduce genetic variation in a population over time.
Genetic drift tends to reduce genetic variation in a population over time.
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Explain how allele frequencies change across generations through natural selection.
Explain how allele frequencies change across generations through natural selection.
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The process through which phenotypic traits become more common in a population over generations due to varying relative fitness is called _______.
The process through which phenotypic traits become more common in a population over generations due to varying relative fitness is called _______.
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Which factor is NOT a mechanism of microevolution?
Which factor is NOT a mechanism of microevolution?
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Study Notes
Microevolution
- Microevolution is a change in allele frequency in a population or species across generations
- Focuses on variation within populations/species and evolutionary change over shorter time periods
- Macroevolution is evolution above the species level
- Focuses on variation among species and questions related to diversification across relatively long periods of time
- Four processes cause microevolution: mutation, gene flow, genetic drift, and natural selection
- Microevolution requires genetic variation (more than one allele segregating at a locus in a population)
Learning Objectives
- Differentiate micro and macroevolution and the processes causing the latter, and the sources of genetic variance
- Contrast random and non-random mating, explaining the effects on allele and genotype frequencies
- Define inbreeding and inbreeding depression, outlining causes and mechanisms that reduce inbreeding likelihood
- Identify types of mutations, their classification in terms of fitness effects (beneficial, neutral, deleterious) and how relative frequencies differ
- Discuss how mutation impacts allele frequencies and the creation of genetic variation
- Define gene flow and compare it with mutation in terms of their roles in altering allele frequencies and creating genetic variation
- Examine how gene flow and spatially varying selection interact to affect local adaptation
- Define genetic drift, explaining how population size affects allele frequencies and genetic variation/population divergence; also summarize effects of bottlenecks and founder events
- Outline the human health implications due to genetic drift
- Define natural selection and fitness
- Summarize the approaches to detecting natural selection, and the associated problem with correlated traits
- Detail how genetic variation can be maintained
Introduction
- Microevolution : a change in allele frequency in a population over generations that focuses on changes within a single species
- Macroevolution: a larger scale change (evolving to a new species, or related species) across longer time scales than microevolution
- Four processes that can cause microevolution: mutation, gene flow, genetic drift and natural selection
- Microevolution requires genetic variation
Mathematics of Microevolution
- Population and quantitative genetics provide rigorous mathematical frameworks for studying the impacts of assortative mating and the microevolutionary processes of mutation, gene flow, genetic drift and selection on Mendelian variation and quantitative traits
Outline
- 4.1 Non-random mating
- 4.2 Mutation
- 4.3 Gene flow
- 4.4 Genetic drift
- 4.5 Natural selection
Random Mating
- Individuals mate randomly with respect to their genotype at a particular locus of interest
- Also called panmixia
- Some species exhibit panmixia, but most have geographic structuring into populations
Non-random mating
- Mating may occur between relatives more or less frequently/more or less often than expected by chance (called inbreeding and outbreeding respectively)
- Individuals may self-fertilize more or less often than expected
- Individuals may mate more frequently with other individuals that are more or less similar in phenotype (called assortative and disassortative mating, respectively)
- Non-random mating affects allele frequencies - homozygosity or heterozygosity
Inbreeding
- Inbreeding is mating between related individuals
- Inbreeding increases the frequency of homozygotes and decreases heterozygosity
- Inbreeding depression: a decrease in fitness that may result from inbreeding
Inbreeding Depression
- The increase in homozygosity resulting from inbreeding tends to lower fitness
- Widespread phenomenon (not just seen in royals)
- Can exacerbate the loss of genetic variation (allele diversity) that occurs in small populations due to genetic drift
- Has implications impacting conservation biology and human health
Mendelian Causes of Inbreeding Depression
- Dominance Hypothesis: Deleterious alleles are recessive. Heterozygotes hide the effects of the allele, so inbreeding leads to a higher expression of negative effects
- Heterozygote Advantage: Heterozygotes are more fit than either homozygote. Inbreeding reduces heterozygosity, leading to lower fitness
Inbreeding Avoidance
- Many plants and animals have evolved traits that reduce the likelihood of inbreeding
- These include:
- Kin recognition
- Dispersal
- Delayed maturation/reproductive suppression
- Extra-pair copulations
- Hermaphrodites/monoecious species have features that prevent self-fertilization
Outbreeding
- Outbreeding occurs when individuals are less related than expected by random mating
- Increase in heterozygosity and decrease in homozygosity
- Can improve fitness compared to non-outbred individuals
Inbreeding/Outbreeding in Agriculture
- Nearly all corn in developed nations is F1 cross between inbred lines
- These populations are maintained by repeated inbreeding across many gens
- This ensures that almost all genetic variation is lost and single genotypes are fixed
- Selection of specific genotypes can be maintained for better performance
Mutation
- Mutation is a change in the genetic information (DNA)
- Arises from DNA replication, recombination or repair errors, environmental or chemical mutagens
- Creates new alleles
- Is an ultimate source of genetic variation
- Random (not directional)
- Can be transmitted if present in the germ line
- Can have variable effects on an organism
Types of Mutation
- Small scale (point mutation):
- Substitution: one nucleotide is replaced with another (silent or replacement)
- Insertion/Deletion: one or more nucleotides are added or removed (Frameshift)
- Large scale: mutations in chromosomal structure (translocations, inversions, loss, duplications)
Mutation Rates
- Relatively rare per nucleotide site, but rates vary among taxa (10⁻⁷ to 10⁻¹¹ mutations/base pair/generation)
- In humans, a large number of mutations still occur each generation due to genome size
Impacts of Mutation
- Most new mutations are deleterious
Gene Flow
- Gene flow is the movement of alleles between populations (migration of individuals or gametes)
- Introduces and removes alleles from a population
- Generally larger effect than mutation on allele frequencies
- Homogenizes populations by reducing genetic differences
- If gene flow is very high, population differences are lost
Gene flow and local adaptation
- Gene flow can impede adaptation by constantly introducing maladaptive alleles
- Can also promote adaptation by spreading beneficial alleles
Example: Fugitive Atlantic Salmon
- See example in Campbell (Fig. 23.11 and accompanying text)
Genetic Drift
- Finite populations are subject to random changes in allele frequencies across generations
- Process is called genetic drift
- Occurs due to sampling variation
Effects of Genetic Drift
- Random changes in allele frequencies
- Magnitude of change is inversely related to population size (smaller populations have stronger drift)
- On average reduces genetic variation because alleles are lost
- In small populations, drift can overwhelm selection
- Drift causes populations to diverge
- Drift-induced deviations from expected genotype frequencies are usually small in larger populations
Simulating Genetic Drift
- Use simulations to observe genetic drift in replicate populations across various scenarios (e.g., varying population size, frequency of allele A1, and migration)
Population Bottlenecks
- Severe (generally rapid) reductions in population size
- Reduces genetic variation and enhances genetic drift
- Caused by environmental factors, human activity or disease
- Can result from founder effects (small group of individuals colonizes a new area)
Mutation-drift: human health implications
- Population bottlenecks can result in increased frequency of deleterious mutations
Natural Selection
- Natural selection occurs when certain conditions are met:
- Individuals vary in a trait
- There's a non-random association between the trait and reproductive success (Darwinian fitness)
- The trait is heritable
- Traits evolve when there's differential reproductive success based on the trait and traits are heritable
Fitness
- Darwinian fitness: the absolute contribution of an individual to the next generation
- Reporductive success measured as the number of offspring an individual produces
- Natural selection arises from variation in relative fitness: comparing the contribution of an individual to the next generation relative to other individuals
Genotype-Phenotype
- Natural selection acts on phenotypes
- Genetic variation underlies phenotypic variation
- Alleles associated with advantageous/fitness-enhancing phenotypes are passed more frequently
- Changes in allele frequencies across generations lead to changes in the distribution of traits among individuals
Example: DDT Resistance in Insects
- France's use of pesticides led to DDT resistance in insects
- Resistance occurred due to a single mutation in an esterase gene that allows breakdown of toxins like DDT
- The mutation rapidly spread throughout populations
Components of fitness & types of selection
- Fitness has components of
- survivorship/viability
- fecundity
- mating success
- Types of selection
- Viability
- Fecundity
- Sexual
Forms of Selection
- Linear/directional
- Stabilizing
- Disruptive
Detecting Natural Selection
- Direct measurement (observational and often experimental study)
Problem of Correlated Traits
- Traits are often correlated (due to pleiotropy or physical linkage)
- Direct selection on one trait can induce correlated response in other traits
- Selection isn't necessarily acting on a trait directly
Other Forms of Selection: frequency-dependent selection
- Fitness of a phenotype depends on its frequency in a population
- Positive frequency dependence: directional selection increases as the phenotype becomes more common
- Negative frequency dependence: directional selection is stronger when the phenotype is less common (balancing selection)
Other Forms of Selection: Heterozygote Advantage
- Heterozygotes have higher fitness compared to homozygotes which maintains genetic variation
- Example: sickle-cell anemia, where heterozygotes are resistant to malaria
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Description
Test your understanding of microevolution with this quiz that covers key processes, definitions, and relationships with macroevolution. Assess your knowledge of genetic variation, mating patterns, and the impact of gene flow and genetic drift. Perfect for biology students looking to deepen their grasp of evolutionary concepts.
