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What is the primary mechanism that causes a population to evolve?
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.
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Match the mechanisms of microevolution with their descriptions:
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During the drought on Daphne Major, which type of finch survived better?
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Genetic variation is not necessary for natural selection to occur.
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What were the population numbers of G.fortis before and after the drought?
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What term is used to describe differences among individuals in their genetic makeup?
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Darwin was aware of how organisms pass genetic traits to their offspring.
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What are genes?
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Mendel's experiments with _____ plants revealed fundamental principles of genetics.
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Match the type of phenotypic variation with its description:
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Which of the following reflects phenotypic variation identified among individuals?
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Phenotypic traits can vary in a gradient along a continuum.
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What effect does natural selection have on heritable traits?
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How many functional olfactory receptor genes do humans have?
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Mice have approximately 1,000 functional olfactory receptor genes.
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What is the average mutation rate in animals per generation?
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The HIV virus has a generation time of about _____ days.
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Match the mechanism of sexual reproduction to its description:
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What is the main benefit of using 'cocktails' in AIDS treatments?
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What three mechanisms contribute to genetic variation in sexually reproducing organisms?
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The mutations in prokaryotes occur at a higher rate than in plants and animals.
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What is the average percentage of loci that are heterozygous in the fruit fly Drosophila melanogaster?
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Nucleotide variability always results in phenotypic variation.
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What is the impact of a 'point mutation'?
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Genetic variation is essential for _____ changes to occur.
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Match the types of genetic variation with their descriptions:
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Which of the following best explains why many mutations do not affect phenotype?
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Heterozygote protection allows harmful recessive alleles to persist in a population.
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What is a consequence of gene duplication in evolution?
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In multicellular organisms, mutations in _____ cells can be passed to offspring.
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Match the genetic processes with their influences on variation:
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What role does sexual reproduction play in genetic variation?
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Most mutations in somatic cells are inherited by the next generation.
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What is meant by nucleotide variability?
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A harmful recessive allele can be propagated in _____ individuals.
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Match the following terms with their definitions:
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What does the Hardy-Weinberg equation assess in a population?
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Allele frequencies in a population must sum to more than 1 if there are two alleles.
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What is the term for a population that remains constant over generations due to no evolution?
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In a non-evolving population, allele and genotype frequencies will remain constant due to only _______ and recombination of alleles.
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Match the following terms with their definitions:
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Which condition is NOT required for a population to be in Hardy-Weinberg equilibrium?
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If observed data is identical to Hardy-Weinberg predictions, we conclude that evolution is occurring.
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What do p and q represent in the context of genetic loci in a population?
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What effect does gene flow have on island snake populations?
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Natural selection can eliminate alleles that are beneficial to populations receiving gene flow.
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What has contributed to the worldwide spread of insecticide resistance alleles in mosquitoes?
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Mating between members of populations with previously little contact leads to an exchange of __________.
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Match the following terms with their descriptions regarding gene flow:
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What is the frequency of carriers (heterozygotes) for PKU in the U.S. population?
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The Hardy-Weinberg equation can accurately predict allele frequencies only when specific conditions are met.
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What is the dominant allele frequency for PKU?
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The founder effect occurs when a few individuals become isolated from a larger ___________.
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Match the following effects to their descriptions:
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In the context of PKU, how is the allele frequency represented in the Hardy-Weinberg equation?
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If new mutations are introduced into a population, it violates one of the Hardy-Weinberg conditions.
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What is the estimated occurrence rate of PKU in newborns?
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The frequency of homozygotes for PKU is calculated as __________.
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Match the following terms to their meanings:
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Which of the following factors can alter allele frequencies in populations?
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Gene flow can occur when individuals migrate between populations.
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What is a major consequence of the bottleneck effect?
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Natural selection can only occur if there is __________ variation among individuals.
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What is the expected frequency of the genotype CRCR in the next generation if the frequency of allele CR is 0.8?
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If allele frequencies remain constant over generations, the population is in Hardy-Weinberg equilibrium.
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What is the Hardy-Weinberg equation for a locus with two alleles?
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The probability that a sperm contains a CW allele is _____ if its frequency is 0.2.
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Match each condition of Hardy-Weinberg equilibrium with its consequence if the condition does not hold:
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Which of the following is NOT a condition for Hardy-Weinberg equilibrium?
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In a population that meets Hardy-Weinberg conditions, changes in genotype frequencies indicate evolution.
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How can allele frequencies be altered in a population?
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The expected frequency of heterozygotes in a population can be calculated using the formula _____ where p and q are allele frequencies.
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What percentage of the wildflower population is expected to have the genotype CWCW if the frequency of allele CW is 0.2?
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Genetic drift has a more significant effect on small populations than on large populations.
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Explain the importance of random mating in maintaining Hardy-Weinberg equilibrium.
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If a population is continuously exposed to natural selection, it is likely to _____ over time.
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Which situation would violate the condition of no gene flow in a population?
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What was the approximate population of greater prairie chickens in Illinois by 1993?
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Genetic drift can increase genetic variation within a population.
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What impact did adding 271 birds from neighboring states have on the egg-hatching rate of the Illinois greater prairie chickens?
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Genetic drift can cause alleles that are slightly harmful to become ______.
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What primarily drives allele frequency changes in gene flow?
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Natural selection consistently favors some alleles over others in the same environment.
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During which decades were the two sets of greater prairie chickens collected that were used for DNA analysis?
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The frequency of harmful alleles can increase due to ______ in small populations.
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Match the terms with their correct descriptions:
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Which factor contributed to the low egg-hatching rate of the small prairie chicken population?
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Gene flow tends to increase genetic differences between populations.
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What was the main outcome when new alleles entered the Illinois prairie chicken population?
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Due to genetic drift, alleles may become ______ or lost over time.
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Match the prairie chicken population years with their respective counts:
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The introduction of which trait in island populations of the Lake Erie water snake demonstrated the impact of natural selection?
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What does natural selection primarily increase in a population?
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Natural selection operates directly on genotypes rather than phenotypes.
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What term describes the contribution of an individual to the gene pool of the next generation relative to others?
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Natural selection can alter the distribution of heritable traits through ______, ______, and ______ selection.
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Match the types of selection with their descriptions:
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Which statement is correct regarding the concept of 'survival of the fittest'?
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The struggle for existence only involves direct competitions among individuals.
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What is the main advantage of a barnacle that is more efficient at collecting food?
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What type of selection favors individuals at both extremes of a phenotypic range?
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Stabilizing selection increases variation within a population.
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What is the result of directional selection in populations?
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In sexual selection, traits that help individuals attract mates are called _______.
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Which of the following is not a result of natural selection?
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Heterozygote advantage leads to the maintenance of multiple alleles at a locus.
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Give an example of an adaptation that aids in survival.
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Disruptive selection is exemplified by the black-bellied seedcracker finches that exhibit _______ bill sizes.
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In which form of selection do individuals compete primarily for mates within the same sex?
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Natural selection can lead to genetic differences between populations.
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What is the primary influence of gene flow in populations?
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Match the type of selection with its description:
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What is one implication of sexual selection?
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The mechanism of evolution that consistently leads to adaptive evolution is _______.
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What type of selection does heterozygote advantage represent if the phenotype is intermediate to both homozygotes?
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Homozygous recessive individuals are protected against malaria due to sickle-cell disease.
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What is the primary reason that adaptations in organisms are often compromises?
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In areas where malaria is common, selection favors _______ individuals over both homozygous dominant and homozygous recessive individuals.
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Match the evolutionary constraints with their descriptions:
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What is one consequence of the sickle-cell allele's prevalence in certain regions?
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Natural selection guarantees the creation of perfect organisms.
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What does evolution co-opt existing structures refer to?
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Natural selection operates on a '______' basis, focusing on the fittest traits available.
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Which of the following describes how sickle-cell disease affects red blood cells?
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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.
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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!