S138-Yamato Shiota - AP Biology Unit 7 First Half Study Guide

Chapter 22: Evolution and Natural Selection

Key Concepts

• Natural Selection vs. Evolution

  • Darwin’s original phrase refers to natural selection as a process that leads to evolution, which is a broader concept encompassing all changes in species over time.

Fossils and Stratification

• Importance of Fossils

  • Fossils provide evidence of past life forms and can show how species have changed over time.

  • Strata Layers: Layers of sedimentary rock that contain fossils can indicate the relative ages of organisms.

• Radiometric Dating

  • A method used to date materials by measuring the decay of radioactive isotopes, contributing to the understanding that the Earth is much older than previously thought.

Paleontology

• Paleontology is the study of fossils, crucial for understanding evolutionary history.

Historical Observations

• Observations such as geological events, erosion, and sedimentation indicated an ancient Earth, contrary to earlier beliefs.

Lamarck's Hypothesis

• Lamarck’s hypothesis proposed that organisms could pass on traits acquired during their lifetime, which has been discredited because genetic information is not changed by behavior.

Darwin’s Voyage Data

• Darwin collected various data including morphological and geographical information, observations of species variation, and fossil records.

Adaptation and Natural Selection

• Adaptation: Traits that increase an organism's fitness in a specific environment arise through natural selection.

• Natural Selection

  • A mechanism of evolution where individuals with advantageous traits survive and reproduce.

  • Artificial Selection: Human-facilitated selection for desired traits in organisms.

Observations of Darwin

• Three Broad Observations: (1) Variability among individuals, (2) Overproduction of offspring, and (3) Struggle for existence.

• Two Observations and Inferences:

  1. Individuals vary in heredity traits.

  2. More offspring are produced than can survive, leading to competition; favorable traits accumulate over generations.

Conditions for Natural Selection

• Variation in traits,Heritability, Differential survival and reproduction.

Evolution of Populations

• Evolution occurs at the population level due to genetic changes over generations, not at the individual level.

Evidence for Evolution

• Types include fossil records, biogeography, comparative anatomy, molecular biology, and embryology.

Natural Selection and Medications

• Antibiotics exemplify natural selection as resistant bacteria survive and proliferate, leading to treatment challenges.

Homology vs. Analogy

• Homology: Similarities due to shared ancestry.

• Vestigial Structures: Remnants of features that served a function in the organism's ancestors.

• Analogous Structures: Similar functions but evolved independently.

Convergent Evolution

• The process where unrelated organisms evolve similar traits due to similar environmental pressures.

Endemic Species

• Species unique to a specific geographical area, often due to isolation.

Chapter 23: Microevolution

Microevolution Defined

• Microevolution refers to small-scale evolutionary changes, typically measured in changes in allele frequencies.

Forces Causing Allele Frequency Changes

• Forces include:

  • Natural selection

  • Genetic drift

  • Gene flow

  • Mutation.

Genetic Variation

• Caused by mutations, gene shuffling during meiosis, and sexual reproduction.

Phenotypes and Genes

• Some phenotypes are influenced by multiple genes (polygenic traits).

Mutations

• Mutations can be beneficial, neutral, or harmful, contributing to genetic variation.

Neutral Variation

• Genetic variation that does not affect an organism’s fitness, thus not subject to natural selection.

Duplicated Genes

• Duplicated genes provide raw material for evolution, allowing for functional diversification.

Gene Pools

• The total collection of alleles in a population, used to measure genetic diversity.

Hardy-Weinberg Equations

• Two equations model genetic variation in a population:

  • p + q = 1 (allele frequencies)

  • p² + 2pq + q² = 1 (genotype frequencies).

• Conditions: Large population, no mutations, no gene flow, random mating, and no natural selection.

Microevolution Conditions

• Breaking Hardy-Weinberg conditions leads to changes in allele frequencies and microevolution.

Adaptive Evolution

• Evolution that results in traits better suited to an environment.

Genetic Drift and Effects

• Genetic Drift: Changes in allele frequency due to random sampling events.

  • Founder Effect: Genetic variation reduces when a new population is established by a small group.

  • Bottleneck Effect: A sharp reduction in population size reduces genetic variation.

Gene Flow and Benefits

• The transfer of alleles between populations helps maintain genetic diversity and counteracts the effects of genetic drift.

Evolution and Chance

• Natural selection interacts with chance; beneficial mutations arise randomly, but their success depends on environmental context.

Relative Fitness

• Measure of reproductive success relative to other individuals within the population.

Chapter 24: Speciation and Macroevolution

Speciation and Macroevolution

• Speciation is the process by which new species arise; it's a key facet of macroevolution.

Evidence in Species Determination

• Biologists compare molecular data, morphological features, and reproductive isolation.

Species Concepts

• Various concepts define species, including biological, morphological, ecologic, and phylogenetic species concepts.

• Concepts of Species:

• 1. **Biological Species Concept**: Defines species based on the ability to interbreed and produce viable, fertile offspring. If populations can mate and produce offspring that can reproduce, they are considered the same species.

• 2. **Morphological Species Concept**: Classifies species based on observable physical traits and characteristics. This approach relies on measurable features such as size, shape, and structural differences.

• 3. **Ecological Species Concept**: Defines species by their ecological niche and the roles they play in their environment. This concept considers factors such as habitat, resource use, and interactions with other species.

• 4. **Phylogenetic Species Concept**: Defines species based on their evolutionary ancestry and relationships. This concept utilizes genetic data and phylogenetic trees to identify groups that share a common ancestor, differentiating them from other groups.

Reproductive Isolation and Hybrids

• Reproductive isolation prevents species from interbreeding; hybrids are offspring from different species.

Pre and Postzygotic Barriers

• Prezygotic Barriers: Prevent mating or fertilization.

• Postzygotic Barriers: Prevent hybrid offspring from developing into viable adults.

Limits of Biological Species Concept

• The biological concept does not apply well to asexual organisms or extinct species.

Allopatric vs. Sympatric Speciation

• Allopatric Speciation: Occurs when populations are geographically isolated.

• Sympatric Speciation: Occurs within overlapping populations often due to behavioral changes, polyploidy, or habitat differentiation.

Polyploidy and Selection

• Autopolyploid: An organism with multiple chromosome sets from the same species.

• Allopolyploid: An organism with sets from different species.

Hybrid Zones

• Regions where different species meet and mate; their fitness varies depending on environmental conditions.

Environmental Effects on Hybrid Zones

• Environmental changes can alter the dynamics of hybrid zones, supporting or reducing hybrid survival.

Reinforcement, Fusion, Stability

• Reinforcement: Strengthening of reproductive barriers.

• Fusion: Species merge due to reduced barriers.

• Stability: Hybrids continue to be produced, maintaining a balance.

Speciation Duration

• Speciation can occur rapidly or over long periods, influenced by various factors.

Punctuated vs. Gradual Models

• Punctuated Equilibrium: Speciation occurs in rapid bursts.

• Gradual Model: Speciation occurs slowly over time.

Prezygotic Barriers

Prezygotic barriers are mechanisms that prevent mating or fertilization between different species before a zygote (fertilized egg) can form. These barriers can include:

• Temporal Isolation: Species may breed at different times of the day or year, so they never meet.

• Habitat Isolation: Different species may live in different environments, preventing them from encountering each other.

• Behavioral Isolation: Unique behaviors or mating rituals can attract mates of the same species while deterring others.

• Mechanical Isolation: Anatomical differences prevent successful mating.

• Gametic Isolation: Even if mating occurs, the gametes (sperm and egg) may not be compatible, preventing fertilization.

Postzygotic Barriers

Postzygotic barriers occur after fertilization and prevent the hybrid offspring from developing into viable, fertile adults. These barriers can include:

• Hybrid Inviability: The hybrid offspring may not survive to maturity, often dying at an early stage of development.

• Hybrid Sterility: The hybrids may develop into adults but are sterile and cannot produce viable gametes (e.g., mules, which are hybrids of horses and donkeys).

• Hybrid Breakdown: The first-generation hybrids may be fertile, but their offspring (the next generation) are inviable or sterile. This leads to difficulty in sustaining populations of hybrids over time.

Chapter 22: Evolution and Natural Selection

Key Concepts

• Natural Selection vs. Evolution: Darwin's principle that natural selection drives evolutionary changes, with evolution encompassing all species changes over time.

• Fossils and Stratification: Fossils show past life forms' evolution over time, while stratification reveals the relative ages of organisms through sedimentary layers.

• Radiometric Dating: A method to determine the age of materials by radioactive isotope decay, supporting Earth's significant age.

• Paleontology: The analysis of fossils to understand evolution.

• Lamarck's Hypothesis: Discredited theory suggesting that acquired traits could be inherited.

• Darwin's Data Collection: Important observations on species variation and fossils collected during his voyage.

• Adaptation: Enhanced traits that improve survival and reproduction inherited through natural selection.

• Natural Selection: Evolution mechanism where advantageous traits become more common via survival and reproduction.

• Three Observations of Darwin: Variability among individuals, overproduction of offspring, and the struggle for existence.

• Conditions for Natural Selection: Requires variation, heritability, and differential survival and reproduction.

• Evidence for Evolution: Includes fossil records, biogeography, comparative anatomy, molecular biology, and embryology.

• Natural Selection and Medications: Antibiotic resistance is an example of natural selection affecting pathogens.

Chapter 23: Microevolution

Concepts of Microevolution

• Definition: Small-scale evolutionary changes, usually in allele frequencies.

• Forces Causing Changes: Natural selection, genetic drift, gene flow, and mutation.

• Genetic Variation: Produced by mutations and gene shuffling affecting traits and overall diversity.

• Phenotypes and Genes: Traits can be polygenic and influenced by multiple genes.

• Neutral Variation: Genetic differences that do not affect fitness.

• Duplicated Genes: Serve as a basis for evolutionary divergence and new functions.

• Gene Pools: The complete set of alleles in a population, important for genetic diversity.

• Hardy-Weinberg Equations: Model allele/genotype frequencies in populations under ideal conditions (no evolution factors).

• Adaptive Evolution: Evolves advantageous traits in specific environments.

• Genetic Drift: Random changes in allele frequencies in small populations.

• Founder and Bottleneck Effects: Reductions in genetic variation due to small population establishments or drastic size reductions.

• Gene Flow Benefits: Transfers alleles between populations, aiding diversity and countering genetic drift.

• Relative Fitness: A metric for reproductive success compared to others in the population.

Chapter 24: Speciation and Macroevolution

Concepts of Speciation

• Speciation: The emergence of new species; essential to macroevolution.

• Species Determination: Involves molecular, morphological, and reproductive isolation comparisons.

• Species Concepts: Definitions include biological, morphological, ecological, and phylogenetic concepts.

• Reproductive Isolation and Hybrids: Mechanisms preventing species interbreeding and their hybrid offspring.

• Prezygotic vs. Postzygotic Barriers: Prezygotic barriers prevent mating; postzygotic barriers hinder hybrid viability or fertility.

• Allopatric vs. Sympatric Speciation: Allopatric involves geographical isolation; sympatric occurs within overlapping populations due to behavioral changes or other factors.

• Polyploidy: Some plants can evolve through chromosome duplications leading to speciation

• Hybrid Zones: Locations where different species interbreed, affecting hybrid fitness based on environmental situations.

• Reinforcement, Fusion, Stability: Processes that either strengthen reproductive barriers, merge species, or maintain hybrid production.

• Speciation Duration and Models: Speciation can be rapid or gradual, categorized as punctuated equilibrium or gradual models.

Chapter 23: Microevolution - Overview and Key Concepts

Microevolution refers to small-scale evolutionary changes that typically manifest as changes in allele frequencies within a population. Understanding the forces that drive these changes is crucial for grasping the dynamics of evolution.

Types of Selection

1. Directional Selection: This occurs when natural selection favors one extreme phenotype over the others, leading to a shift in the population's frequency distribution toward that phenotype. An example is the increase in size of a particular species in response to environmental changes.

2. Disruptive Selection: In this case, both extreme phenotypes are favored over intermediate phenotypes, which can lead to the formation of two or more contrasting phenotypes in the same population. An example can be seen in African seedcracker birds, where individuals with very large or very small beaks have a foraging advantage over those with medium-sized beaks.

3. Stabilizing Selection: This type of selection favors intermediate phenotypes and acts against extreme traits. By reducing variation, stabilizing selection can maintain the status quo for a particular trait, such as human birth weight, where very low or very high weights can be detrimental.

4. Sexual Selection: This is a form of natural selection where individuals with certain inherited traits are more successful at attracting mates.

   • Sexual Dimorphism: This refers to the differences in appearance between males and females of the same species, often due to sexual selection. Examples include the bright plumage of male birds compared to their more camouflaged female counterparts.

   • Intrasexual Selection: Competition among individuals of one sex (usually males) for access to mates.

   • Intersexual Selection: Involves individuals of one sex (typically females) choosing mates based on desirable traits.

5. Balancing Selection: Maintains genetic diversity in a population by favoring more than one phenotype. It can include mechanisms such as frequency-dependent selection or heterozygous advantage, where heterozygous individuals (those carrying two different alleles for a trait) have a selective advantage over homozygous individuals.

6. Frequency-Dependent Selection: The fitness of a phenotype depends on its frequency relative to other phenotypes in a given population. This can stabilize a certain trait within the population as its success depends on how common or rare it is.

7. Heterozygous Advantage: Occurs when individuals carrying two different alleles for a trait (heterozygotes) have a higher fitness than those who are homozygous. A classic example is seen in sickle cell trait, where heterozygous individuals are more resistant to malaria compared to homozygous individuals.

Why Evolution Cannot Create a Perfect Organism

Evolution cannot create a perfect organism due to several inherent limitations:

1. Adaptation to Current Environments: Organisms evolve to adapt to current conditions, which may change over time. A trait that is beneficial today may not be advantageous in the future.

2. Genetic Constraints: Evolution works with the existing genetic variation within a population. New traits can only arise from mutations or recombinations of existing genes, which can limit the potential for 'perfection.'

3. Trade-offs: Many adaptations come with trade-offs. For example, larger size may confer advantages in one context while making organisms more vulnerable in another.

4. Random Events: Evolution is influenced by random genetic drift and mutations, which can lead to unpredictable changes that do not necessarily lead to perfection.

5. Environmental Variability: Different environments select for different traits, meaning what is optimal in one setting may be a disadvantage in another.

Overall, evolution is a complex process influenced by multiple factors that lead to the optimization of traits rather than the creation of perfect organisms.