Evolution and Natural Selection Quiz
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What is the primary mechanism that causes a population to evolve?

  • Genetic drift
  • Natural selection (correct)
  • Mutations
  • Gene flow

    • Individual organisms evolve over time.

    False

    What is microevolution?

    A change in allele frequencies in a population over generations.

    The medium ground finch is known for its ability to eat _____ seeds.

    <p>hard</p> Signup and view all the answers

    Match the mechanisms of microevolution with their descriptions:

    <p>Natural selection = Improves organism's adaptation to the environment Genetic drift = Chance events affecting allele frequencies Gene flow = Transfer of alleles between populations</p> Signup and view all the answers

    During the drought on Daphne Major, which type of finch survived better?

    <p>Finches with deep beaks</p> Signup and view all the answers

    Genetic variation is not necessary for natural selection to occur.

    <p>False</p> Signup and view all the answers

    What were the population numbers of G.fortis before and after the drought?

    <p>Before: 1200 birds, After: 180 birds.</p> Signup and view all the answers

    What term is used to describe differences among individuals in their genetic makeup?

    <p>Genetic variation</p> Signup and view all the answers

    Darwin was aware of how organisms pass genetic traits to their offspring.

    <p>False</p> Signup and view all the answers

    What are genes?

    <p>Discrete heritable units that are transmitted from parents to offspring.</p> Signup and view all the answers

    Mendel's experiments with _____ plants revealed fundamental principles of genetics.

    <p>pea</p> Signup and view all the answers

    Match the type of phenotypic variation with its description:

    <p>Either-or variation = Determined by a single gene locus Continuous variation = Influenced by two or more genes</p> Signup and view all the answers

    Which of the following reflects phenotypic variation identified among individuals?

    <p>Both A and B</p> Signup and view all the answers

    Phenotypic traits can vary in a gradient along a continuum.

    <p>True</p> Signup and view all the answers

    What effect does natural selection have on heritable traits?

    <p>Natural selection favors individuals with advantageous heritable traits, leading to evolutionary change.</p> Signup and view all the answers

    How many functional olfactory receptor genes do humans have?

    <p>380</p> Signup and view all the answers

    Mice have approximately 1,000 functional olfactory receptor genes.

    <p>False</p> Signup and view all the answers

    What is the average mutation rate in animals per generation?

    <p>one mutation in every 100,000 genes</p> Signup and view all the answers

    The HIV virus has a generation time of about _____ days.

    <p>two</p> Signup and view all the answers

    Match the mechanism of sexual reproduction to its description:

    <p>Crossing over = Homologous chromosomes exchange alleles Independent assortment = Random distribution of alleles into gametes Fertilization = Combination of gametes from different genetic backgrounds</p> Signup and view all the answers

    What is the main benefit of using 'cocktails' in AIDS treatments?

    <p>To minimize the development of resistant mutations</p> Signup and view all the answers

    What three mechanisms contribute to genetic variation in sexually reproducing organisms?

    <p>crossing over, independent assortment, fertilization</p> Signup and view all the answers

    The mutations in prokaryotes occur at a higher rate than in plants and animals.

    <p>True</p> Signup and view all the answers

    What is the average percentage of loci that are heterozygous in the fruit fly Drosophila melanogaster?

    <p>14%</p> Signup and view all the answers

    Nucleotide variability always results in phenotypic variation.

    <p>False</p> Signup and view all the answers

    What is the impact of a 'point mutation'?

    <p>It can significantly affect phenotype.</p> Signup and view all the answers

    Genetic variation is essential for _____ changes to occur.

    <p>evolutionary</p> Signup and view all the answers

    Match the types of genetic variation with their descriptions:

    <p>Heterozygous = Two different alleles at a locus Homozygous = Two identical alleles at a locus Point Mutation = Change of a single nucleotide Gene Duplication = Increase in the number of copies of a gene</p> Signup and view all the answers

    Which of the following best explains why many mutations do not affect phenotype?

    <p>They occur in noncoding regions or cause no change in protein structure.</p> Signup and view all the answers

    Heterozygote protection allows harmful recessive alleles to persist in a population.

    <p>True</p> Signup and view all the answers

    What is a consequence of gene duplication in evolution?

    <p>It can lead to new genes that may acquire new functions.</p> Signup and view all the answers

    In multicellular organisms, mutations in _____ cells can be passed to offspring.

    <p>gamete</p> Signup and view all the answers

    Match the genetic processes with their influences on variation:

    <p>Mutation = Source of new alleles Gene Duplication = Expansion of genome Sexual Reproduction = Rearrangement of existing genes Chromosomal Rearrangement = Potentially beneficial changes</p> Signup and view all the answers

    What role does sexual reproduction play in genetic variation?

    <p>It rearranges existing genes in offspring.</p> Signup and view all the answers

    Most mutations in somatic cells are inherited by the next generation.

    <p>False</p> Signup and view all the answers

    What is meant by nucleotide variability?

    <p>Variation in the nucleotide sequences of DNA.</p> Signup and view all the answers

    A harmful recessive allele can be propagated in _____ individuals.

    <p>heterozygous</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Exons = Coding regions of a gene Introns = Noncoding segments between exons Phenotype = The observable characteristics of an organism Genotype = The genetic constitution of an organism</p> Signup and view all the answers

    What does the Hardy-Weinberg equation assess in a population?

    <p>Whether evolution is occurring</p> Signup and view all the answers

    Allele frequencies in a population must sum to more than 1 if there are two alleles.

    <p>False</p> Signup and view all the answers

    What is the term for a population that remains constant over generations due to no evolution?

    <p>Hardy-Weinberg equilibrium</p> Signup and view all the answers

    In a non-evolving population, allele and genotype frequencies will remain constant due to only _______ and recombination of alleles.

    <p>Mendelian segregation</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>p = Frequency of one allele in a population q = Frequency of the other allele in a population Hardy-Weinberg equilibrium = Condition where allele frequencies remain constant Evolution = Change in genetic makeup of a population over time</p> Signup and view all the answers

    Which condition is NOT required for a population to be in Hardy-Weinberg equilibrium?

    <p>Small population size</p> Signup and view all the answers

    If observed data is identical to Hardy-Weinberg predictions, we conclude that evolution is occurring.

    <p>False</p> Signup and view all the answers

    What do p and q represent in the context of genetic loci in a population?

    <p>Allele frequencies</p> Signup and view all the answers

    What effect does gene flow have on island snake populations?

    <p>It prevents the complete removal of alleles for banded coloration.</p> Signup and view all the answers

    Natural selection can eliminate alleles that are beneficial to populations receiving gene flow.

    <p>False</p> Signup and view all the answers

    What has contributed to the worldwide spread of insecticide resistance alleles in mosquitoes?

    <p>Gene flow</p> Signup and view all the answers

    Mating between members of populations with previously little contact leads to an exchange of __________.

    <p>alleles</p> Signup and view all the answers

    Match the following terms with their descriptions regarding gene flow:

    <p>Gene flow = Transfer of alleles between populations Insecticide resistance = Increased survival due to mutations Mating between populations = Exchange of genetic material Natural selection = Process favoring advantageous traits</p> Signup and view all the answers

    What is the frequency of carriers (heterozygotes) for PKU in the U.S. population?

    <p>0.0198</p> Signup and view all the answers

    The Hardy-Weinberg equation can accurately predict allele frequencies only when specific conditions are met.

    <p>True</p> Signup and view all the answers

    What is the dominant allele frequency for PKU?

    <p>0.99</p> Signup and view all the answers

    The founder effect occurs when a few individuals become isolated from a larger ___________.

    <p>population</p> Signup and view all the answers

    Match the following effects to their descriptions:

    <p>Founder Effect = Occurs when a small group starts a new population Bottleneck Effect = Occurs after a dramatic reduction in population size Genetic Drift = Chance events alter allele frequencies Natural Selection = Survival and reproduction based on advantageous traits</p> Signup and view all the answers

    In the context of PKU, how is the allele frequency represented in the Hardy-Weinberg equation?

    <p>q^2</p> Signup and view all the answers

    If new mutations are introduced into a population, it violates one of the Hardy-Weinberg conditions.

    <p>True</p> Signup and view all the answers

    What is the estimated occurrence rate of PKU in newborns?

    <p>1 in 10,000</p> Signup and view all the answers

    The frequency of homozygotes for PKU is calculated as __________.

    <p>0.0001</p> Signup and view all the answers

    Match the following terms to their meanings:

    <p>Heterozygote = An individual with two different alleles Homozygote = An individual with two identical alleles Recessive allele = An allele that is masked by a dominant allele Dominant allele = An allele that expresses its trait when present</p> Signup and view all the answers

    Which of the following factors can alter allele frequencies in populations?

    <p>Natural selection</p> Signup and view all the answers

    Gene flow can occur when individuals migrate between populations.

    <p>True</p> Signup and view all the answers

    What is a major consequence of the bottleneck effect?

    <p>Reduced genetic variation</p> Signup and view all the answers

    Natural selection can only occur if there is __________ variation among individuals.

    <p>genetic</p> Signup and view all the answers

    What is the expected frequency of the genotype CRCR in the next generation if the frequency of allele CR is 0.8?

    <p>0.64</p> Signup and view all the answers

    If allele frequencies remain constant over generations, the population is in Hardy-Weinberg equilibrium.

    <p>True</p> Signup and view all the answers

    What is the Hardy-Weinberg equation for a locus with two alleles?

    <p>p^2 + 2pq + q^2 = 1</p> Signup and view all the answers

    The probability that a sperm contains a CW allele is _____ if its frequency is 0.2.

    <p>0.2</p> Signup and view all the answers

    Match each condition of Hardy-Weinberg equilibrium with its consequence if the condition does not hold:

    <p>No mutations = The gene pool is modified Random mating = Genotype frequencies change No natural selection = Allele frequencies change due to survival differences Extremely large population size = Genetic drift affects allele frequencies No gene flow = Allele frequencies can change due to movement of alleles</p> Signup and view all the answers

    Which of the following is NOT a condition for Hardy-Weinberg equilibrium?

    <p>Presence of mutations</p> Signup and view all the answers

    In a population that meets Hardy-Weinberg conditions, changes in genotype frequencies indicate evolution.

    <p>False</p> Signup and view all the answers

    How can allele frequencies be altered in a population?

    <p>Through mutations, natural selection, genetic drift, non-random mating, and gene flow.</p> Signup and view all the answers

    The expected frequency of heterozygotes in a population can be calculated using the formula _____ where p and q are allele frequencies.

    <p>2pq</p> Signup and view all the answers

    What percentage of the wildflower population is expected to have the genotype CWCW if the frequency of allele CW is 0.2?

    <p>4%</p> Signup and view all the answers

    Genetic drift has a more significant effect on small populations than on large populations.

    <p>True</p> Signup and view all the answers

    Explain the importance of random mating in maintaining Hardy-Weinberg equilibrium.

    <p>Random mating ensures that alleles combine in proportions consistent with their frequencies, stabilizing genotype ratios.</p> Signup and view all the answers

    If a population is continuously exposed to natural selection, it is likely to _____ over time.

    <p>evolve</p> Signup and view all the answers

    Which situation would violate the condition of no gene flow in a population?

    <p>Migration of individuals into the population</p> Signup and view all the answers

    What was the approximate population of greater prairie chickens in Illinois by 1993?

    <p>50</p> Signup and view all the answers

    Genetic drift can increase genetic variation within a population.

    <p>False</p> Signup and view all the answers

    What impact did adding 271 birds from neighboring states have on the egg-hatching rate of the Illinois greater prairie chickens?

    <p>The egg-hatching rate improved to over 90%.</p> Signup and view all the answers

    Genetic drift can cause alleles that are slightly harmful to become ______.

    <p>fixed</p> Signup and view all the answers

    What primarily drives allele frequency changes in gene flow?

    <p>Migration</p> Signup and view all the answers

    Natural selection consistently favors some alleles over others in the same environment.

    <p>True</p> Signup and view all the answers

    During which decades were the two sets of greater prairie chickens collected that were used for DNA analysis?

    <p>1930s and 1960s</p> Signup and view all the answers

    The frequency of harmful alleles can increase due to ______ in small populations.

    <p>genetic drift</p> Signup and view all the answers

    Match the terms with their correct descriptions:

    <p>Genetic drift = Random changes in allele frequencies Gene flow = Transfer of alleles between populations Natural selection = Non-random changes favoring beneficial traits Population bottleneck = Significant reduction in population size</p> Signup and view all the answers

    Which factor contributed to the low egg-hatching rate of the small prairie chicken population?

    <p>Genetic drift</p> Signup and view all the answers

    Gene flow tends to increase genetic differences between populations.

    <p>False</p> Signup and view all the answers

    What was the main outcome when new alleles entered the Illinois prairie chicken population?

    <p>The genetic variation increased.</p> Signup and view all the answers

    Due to genetic drift, alleles may become ______ or lost over time.

    <p>fixed</p> Signup and view all the answers

    Match the prairie chicken population years with their respective counts:

    <p>1930s = 25,000 1960s = 1,000 1993 = Less than 50</p> Signup and view all the answers

    The introduction of which trait in island populations of the Lake Erie water snake demonstrated the impact of natural selection?

    <p>Unbanded coloration</p> Signup and view all the answers

    What does natural selection primarily increase in a population?

    <p>Frequencies of alleles providing reproductive advantage</p> Signup and view all the answers

    Natural selection operates directly on genotypes rather than phenotypes.

    <p>False</p> Signup and view all the answers

    What term describes the contribution of an individual to the gene pool of the next generation relative to others?

    <p>relative fitness</p> Signup and view all the answers

    Natural selection can alter the distribution of heritable traits through ______, ______, and ______ selection.

    <p>directional, disruptive, stabilizing</p> Signup and view all the answers

    Match the types of selection with their descriptions:

    <p>Directional Selection = Favors one extreme phenotype Disruptive Selection = Favors both extreme phenotypes Stabilizing Selection = Favors intermediate phenotypes</p> Signup and view all the answers

    Which statement is correct regarding the concept of 'survival of the fittest'?

    <p>It emphasizes reproductive success over mere survival.</p> Signup and view all the answers

    The struggle for existence only involves direct competitions among individuals.

    <p>False</p> Signup and view all the answers

    What is the main advantage of a barnacle that is more efficient at collecting food?

    <p>It has greater energy stores to produce more offspring.</p> Signup and view all the answers

    What type of selection favors individuals at both extremes of a phenotypic range?

    <p>Disruptive selection</p> Signup and view all the answers

    Stabilizing selection increases variation within a population.

    <p>False</p> Signup and view all the answers

    What is the result of directional selection in populations?

    <p>It shifts the frequency curve of phenotypic traits in one direction.</p> Signup and view all the answers

    In sexual selection, traits that help individuals attract mates are called _______.

    <p>secondary sexual characteristics</p> Signup and view all the answers

    Which of the following is not a result of natural selection?

    <p>Increased genetic drift</p> Signup and view all the answers

    Heterozygote advantage leads to the maintenance of multiple alleles at a locus.

    <p>True</p> Signup and view all the answers

    Give an example of an adaptation that aids in survival.

    <p>The ability of octopuses to change color rapidly.</p> Signup and view all the answers

    Disruptive selection is exemplified by the black-bellied seedcracker finches that exhibit _______ bill sizes.

    <p>two distinctly different</p> Signup and view all the answers

    In which form of selection do individuals compete primarily for mates within the same sex?

    <p>Intrasexual selection</p> Signup and view all the answers

    Natural selection can lead to genetic differences between populations.

    <p>True</p> Signup and view all the answers

    What is the primary influence of gene flow in populations?

    <p>It can introduce new alleles into a population.</p> Signup and view all the answers

    Match the type of selection with its description:

    <p>Directional selection = Favors individuals at one extreme of a phenotypic range Disruptive selection = Favors individuals at both extremes Stabilizing selection = Favors intermediate variants Sexual selection = Favors traits that improve mating success</p> Signup and view all the answers

    What is one implication of sexual selection?

    <p>It can result in sexual dimorphism.</p> Signup and view all the answers

    The mechanism of evolution that consistently leads to adaptive evolution is _______.

    <p>natural selection</p> Signup and view all the answers

    What type of selection does heterozygote advantage represent if the phenotype is intermediate to both homozygotes?

    <p>Stabilizing selection</p> Signup and view all the answers

    Homozygous recessive individuals are protected against malaria due to sickle-cell disease.

    <p>False</p> Signup and view all the answers

    What is the primary reason that adaptations in organisms are often compromises?

    <p>Each organism must perform multiple functions.</p> Signup and view all the answers

    In areas where malaria is common, selection favors _______ individuals over both homozygous dominant and homozygous recessive individuals.

    <p>heterozygote</p> Signup and view all the answers

    Match the evolutionary constraints with their descriptions:

    <p>Selection can act only on existing variations = Natural selection can only favor traits that already exist in the population. Evolution is limited by historical constraints = Evolution builds on and modifies existing anatomical structures. Adaptations are often compromises = Adaptations must balance multiple functional needs. Chance events affect evolutionary history = Random events can influence which individuals are better suited to a new environment.</p> Signup and view all the answers

    What is one consequence of the sickle-cell allele's prevalence in certain regions?

    <p>Higher resistance to malaria</p> Signup and view all the answers

    Natural selection guarantees the creation of perfect organisms.

    <p>False</p> Signup and view all the answers

    What does evolution co-opt existing structures refer to?

    <p>Evolution adapts pre-existing traits for new functions.</p> Signup and view all the answers

    Natural selection operates on a '______' basis, focusing on the fittest traits available.

    <p>better-than</p> Signup and view all the answers

    Which of the following describes how sickle-cell disease affects red blood cells?

    <p>They distort in shape under low-oxygen conditions.</p> Signup and view all the answers

    Study Notes

    Evolution Misconceptions

    • Individual organisms do not evolve; evolution occurs at the population level.
    • Natural selection acts on individuals, affecting survival and reproduction, but its evolutionary impact is seen in populations over time.

    Case Study: Medium Ground Finch

    • The medium ground finch (Geospiza fortis) is a seed-eating bird native to the Galápagos Islands.
    • In 1977, a severe drought drastically reduced the G. fortis population from 1,200 to 180 individuals.
    • During the drought, the availability of small, soft seeds decreased, leading the finches to rely on larger, harder seeds.
    • Birds with larger and deeper beaks were more successful in feeding on these seeds, resulting in a higher survival rate.
    • Beak depth is an inherited trait; offspring of surviving finches exhibited deeper beaks.

    Microevolution

    • Microevolution refers to changes in allele frequencies within a population across generations.
    • The average beak depth in G. fortis increased in the subsequent generation post-drought, demonstrating evolutionary change.
    • Individual finches did not change in size, but the population shifted towards a greater proportion of birds with large beaks.

    Mechanisms of Microevolution

    • Three main mechanisms can cause changes in allele frequencies:
      • Natural Selection: Consistently enhances adaptation, improving organisms' fit to their environment.
      • Genetic Drift: Chance events lead to random changes in allele frequencies.
      • Gene Flow: Involves the transfer of alleles between different populations.

    Importance of Genetic Variation

    • Genetic variation in a population is essential for processes like natural selection and adaptation to take place effectively.

    Evolution and Genetic Variation

    • Darwin's Theory: Proposed natural selection as the main mechanism of evolution, emphasizing that variation in inherited traits is essential.
    • Mendel's Contribution: Established the concept of genes as discrete heritable units, laying groundwork for understanding genetic variation.

    Types of Genetic Variation

    • Individuals exhibit phenotypic variation in traits such as height and facial features; this variation often reflects underlying genetic differences.
    • Either-or Traits: Determined by a single gene locus (e.g., color of pea plant flowers).
    • Continuous Variation: Results from multiple genes influencing a single trait (e.g., human height, horse coat color).

    Measuring Genetic Variation

    • Gene variability can be quantified by the percentage of heterozygous loci; for example, Drosophila melanogaster has about 14% heterozygosity.
    • Nucleotide Variability: Variation at the DNA level often doesn’t lead to phenotypic variation due to most changes occurring in non-coding regions or neutral mutations.

    Phenotypic Variation and Environment

    • Not all phenotypic variation is genetic; environmental factors can influence traits (e.g., bodybuilders do not pass on muscle development).
    • Only genetically determined traits can impact evolutionary processes, highlighting the importance of genetic variation as the foundation for evolution.

    Sources of Genetic Variation

    • Genetic variation arises from mutations, gene duplications, and sexual reproduction.
    • Mutations: Changes in DNA sequences that can be harmful, neutral, or beneficial, affecting phenotype and reproductive success.
    • Heterozygote Protection: Recessive harmful alleles may persist because they remain hidden in heterozygous individuals.

    Mechanisms Increasing Genetic Variation

    • Gene Duplication: Errors during meiosis can duplicate genes, allowing new functions to develop over time, such as the increase in olfactory receptor genes in mammals.
    • Rapid Reproduction: Prokaryotes and viruses can produce mutations quickly due to high generation rates, leading to fast genetic variation.

    Sexual Reproduction and Genetic Shuffling

    • Sexual reproduction contributes to genetic variation through random assortment of alleles via crossing over, independent assortment, and fertilization processes.
    • These mechanisms ensure diverse genetic combinations each generation, enhancing evolutionary potential.

    Implications for Evolution

    • Genetic variation is critical for natural selection, adaptability, and ultimately the survival of species as environments change over time.

    Hardy-Weinberg Equation

    • Used to test if a population is evolving by comparing expected vs. observed genotype frequencies.
    • Alleles represented by frequencies p (dominant) and q (recessive), with p + q = 1.
    • For a locus with two alleles, the genotypic frequencies can be predicted using p² (homozygous dominant), 2pq (heterozygous), and q² (homozygous recessive), which must sum to 1.

    Hardy-Weinberg Equilibrium

    • A non-evolving population maintains constant allele and genotype frequencies across generations.
    • Conditions for this equilibrium include:
      • No mutations
      • Random mating
      • No natural selection
      • Extremely large population size
      • No gene flow

    Application of Hardy-Weinberg

    • Useful for estimating allele frequencies in inherited diseases like phenylketonuria (PKU).
    • If one in 10,000 births has PKU (q² = 0.0001), then q = 0.01, p = 0.99, and carrier frequency (heterozygotes) is approximately 2%.

    Mechanisms of Evolutionary Change

    • Changes in population genetics can arise from:
      • Natural selection
      • Genetic drift
      • Gene flow

    Founder Effect

    • Occurs when a small group diverges from a larger population, resulting in a new population with differing allele frequencies.
    • Example: The high rate of certain genetic disorders in isolated human populations due to limited founding gene pools.

    Bottleneck Effect

    • A drastic reduction in population size can lead to significant genetic drift, altering allele frequencies by chance.
    • Example: The severe decline of the greater prairie chicken's population led to a loss of genetic variation and lower hatching rates.

    Consequences of Genetic Drift

    • Significant in small populations where chance events greatly influence allele representation.
    • Random changes in allele frequencies can lead to loss of genetic diversity, potentially making populations less adaptable.
    • Harmful alleles may become fixed, jeopardizing population survival.

    Gene Flow

    • The transfer of alleles between populations can reduce genetic differences, promoting homogenization.
    • Example: Pollen transfer between differing populations can alter allele frequencies and adaptations, as observed in Lake Erie water snakes with different color patterns on mainland and islands.

    Summary of Key Effects

    • Genetic drift leads to random shifts in allele frequencies.
    • Founder effect results in a new population with potentially different genetic makeup.
    • Bottleneck effect can result from environmental changes leading to decreased genetic variation.
    • Gene flow facilitates genetic mixing, which can contribute to adaptation or alleviate local variability.### Snakes and Natural Selection
    • Snakes without bands exhibit better camouflage in island habitats compared to banded snakes.
    • Higher survival rates are observed in unbanded snakes in island populations due to natural selection favoring this trait.
    • Despite the advantages, not all island snakes lack bands because of ongoing gene flow from the mainland.

    Gene Flow and Its Consequences

    • Annually, 3 to 10 snakes migrate from the mainland to the islands, introducing banded coloration alleles to local populations.
    • This influx of genetic material inhibits complete adaptation to island conditions, maintaining some banded traits in the population.

    Insecticide Resistance in Mosquitoes

    • Gene flow has facilitated the spread of insecticide resistance alleles in the mosquito species Culex pipiens, which is a vector for West Nile virus.
    • Unique genetic signatures of these alleles indicate that they originated from specific geographic locations through mutation.
    • In their original populations, these alleles became more prevalent due to the selective advantage they conferred against insecticides, later spreading to other populations.

    Human Evolution and Gene Flow

    • Increased human mobility in modern times has led to more frequent mating between previously isolated populations.
    • This interaction results in allele exchange, reducing genetic differences between populations and contributing to evolutionary change.

    Natural Selection and Adaptive Evolution

    • Natural selection is the primary mechanism driving adaptive evolution, combining chance genetic variations with selective pressures favoring advantageous alleles.
    • Adaptive evolution continuously alters allele frequencies, enhancing reproductive success in changing environments.

    Relative Fitness

    • Relative fitness assesses an individual’s genetic contribution to the next generation, factoring in traits beyond direct competition.
    • Examples include barnacles efficiently gathering food or moths with camouflage, illustrating how specific traits improve survival and reproductive success.

    Modes of Natural Selection

    • Directional Selection: Favors one extreme phenotype, shifting the population's traits; common during environmental changes, such as larger seed availability leading to deeper beak sizes in Galápagos finches.
    • Disruptive Selection: Favors two extreme phenotypes while disadvantaging intermediates; e.g., small and large-billed finches specializing in different seed types.
    • Stabilizing Selection: Favors intermediate phenotypes, reducing variation; seen in human birth weights where extremes face higher mortality risks.

    Adaptations and Environmental Change

    • Organisms exhibit various adaptations like octopuses changing color or snakes with specialized jaws, crucial for enhancing survival and reproduction.
    • Adaptive evolution is dynamic; environmental shifts can redefine advantageous traits and lead to genetic differentiation among populations.

    Genetic Drift and Gene Flow

    • While genetic drift and gene flow can influence allele frequencies, they do not consistently favor adaptive traits like natural selection does.

    Sexual Selection

    • Sexual selection involves individuals with specific inherited traits having increased mating success, leading to sexual dimorphism in size, color, and behavior.
    • Intrasexual Selection: Competition among the same sex for mates; often observed in male combat.
    • Intersexual Selection: Mate choice based on traits such as appearance, affecting gene frequency dynamics.

    Heterozygote Advantage

    • Heterozygous individuals may exhibit greater fitness than homozygotes, leading to the maintenance of multiple alleles in a population.
    • Example includes the sickle-cell allele providing malaria resistance in heterozygotes without causing severe symptoms.

    Limitations of Natural Selection

    • Natural selection only acts on existing variations, not creating new traits on demand.
    • Evolution is influenced by historical constraints, building on ancestral traits rather than starting anew.
    • Adaptations often represent compromises between competing needs, e.g., seals adapting for both swimming and terrestrial movement.
    • Evolution may also be shaped by chance events and unpredictable environmental changes, illustrating the complexity of the adaptive process.

    Imperfections in Evolution

    • Evolution does not yield perfect organisms; it operates on a "better than" basis, leading to evidence of imperfections due to the constraints of adaptation.

    Studying That Suits You

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    Description

    Test your understanding of evolution and natural selection with this informative quiz. Focused on misconceptions about individual organisms and population changes, you'll explore the case of the medium ground finch in the Galápagos Islands. Perfect for students studying evolutionary biology!

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