General Biology: Evolutionary Processes, Speciation, and Population Genetics Study Guide

Evolutionary Processes

Natural Selection

Natural selection is a fundamental mechanism of evolution, describing how certain traits become more common in a population due to differential survival and reproduction. Darwin's postulates outline the requirements for natural selection, and various types exist based on how selection acts on traits.

• Mechanisms: Traits that increase fitness become more prevalent over generations.

• Darwin's Postulates: Variation exists, traits are heritable, more offspring are produced than survive, and survival/reproduction is non-random.

• Types of Selection:

  • Directional Selection: Favors one extreme phenotype.

  • Stabilizing Selection: Favors intermediate phenotypes.

  • Disruptive Selection: Favors both extremes over intermediates.

  • Balancing Selection: Maintains genetic diversity in a population.

• Comparison: Darwin's theory vs. earlier ideas (e.g., Plato, Aristotle, Lamarck).

• Example: Antibiotic resistance in bacteria is a result of natural selection.

Genetic Drift

Genetic drift refers to random changes in allele frequencies, especially in small populations. It can lead to significant genetic changes over time, independent of natural selection.

• Founder Effect: Small group establishes a new population, leading to reduced genetic variation.

• Bottleneck Effect: Population size is drastically reduced, causing loss of genetic diversity.

• Impact: Can result in fixation or loss of alleles.

• Example: Cheetah populations show low genetic diversity due to historical bottlenecks.

Gene Flow

Gene flow is the movement of alleles between populations due to migration. It can introduce new genetic material and alter allele frequencies.

• Effects: Increases genetic diversity within populations, reduces differences between populations.

• Example: Migration of pollen between plant populations.

Mutation

Mutation is the ultimate source of genetic variation, introducing new alleles into a population.

• Role: Provides raw material for evolution; most mutations are neutral or deleterious, but some are beneficial.

• Example: Sickle cell allele arose from a mutation and provides malaria resistance in heterozygotes.

Speciation

Species Concepts

Speciation is the process by which new species arise. Several concepts are used to define species.

• Biological Species Concept: Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.

• Morphological Species Concept: Species are defined by physical characteristics.

• Phylogenetic Species Concept: Species are the smallest monophyletic groups on a phylogenetic tree.

Allopatric Speciation

Allopatric speciation occurs when populations are geographically separated, leading to divergence and formation of new species.

• Vicariance: Physical barrier divides a population (e.g., river, mountain).

• Example: Darwin's finches on the Galápagos Islands.

Selection and Adaptation

Phenotypes and Genotypes

Selection acts on phenotypes, which are the observable traits of organisms, but the underlying genotypes determine these traits.

• Adaptation: Traits that increase fitness in a particular environment.

• Environmental Context: Fitness and adaptation can vary depending on environmental conditions.

• Example: Peppered moth coloration in response to industrial pollution.

Population Genetics

Genetic Diversity

Population genetics studies the distribution and changes of allele frequencies under the influence of evolutionary processes.

• Heterozygosity: Measure of genetic variation; individuals with two different alleles at a locus.

• Homozygosity: Individuals with identical alleles at a locus.

• Factors Affecting Diversity: Mutation, gene flow, genetic drift, selection.

• Example: Hardy-Weinberg equilibrium describes allele and genotype frequencies in a non-evolving population.

$p^2 + 2pq + q^2 = 1$

$p + q = 1$

Animal Reproduction

Asexual vs. Sexual Reproduction

Animals reproduce either asexually or sexually, with each mode having distinct advantages and disadvantages.

• Asexual Reproduction: Offspring are genetically identical to the parent (e.g., budding, fission).

• Sexual Reproduction: Involves fusion of gametes, resulting in genetic variation.

• Comparison Table:

Feature	Asexual Reproduction	Sexual Reproduction
Genetic Variation	Low	High
Speed	Fast	Slower
Energy Requirement	Low	High
Examples	Bacteria, Hydra	Mammals, Birds

Modes of Sexual Reproduction

• Internal Fertilization: Gametes fuse inside the body (e.g., mammals).

• External Fertilization: Gametes fuse outside the body (e.g., fish, amphibians).

• Reproductive Switching: Some species can switch between reproductive modes depending on environmental conditions.

Study Tips

• Review Notes and Slides: Focus on key definitions and examples.

• Understand Key Terms: Make flashcards for terms like genetic drift, gene flow, founder effect, etc.

• Application: Practice applying concepts to real-world examples.

• Group Study: Discuss and teach concepts to peers.

• Ask Questions: Seek clarification during office hours if needed.

Additional Resources

• Textbook Chapters: Ch. 22, 23, 24 (up to and including 24.2) and 47 (up to and including 47.3)

Exam Day Tips

• Get a good night's sleep before the exam.

• Eat before the exam to fuel your brain.

• Arrive early with necessary supplies.

• Read each question carefully and manage your time wisely.