Comprehensive Study Guide: Evolution, Diversity, and Ecology (BIO 1331, Ch. 13-14, 22-32, 49-54)

Meiosis and Mendelian Genetics

Meiosis: Mechanisms and Genetic Diversity

Meiosis is a specialized form of cell division that reduces the chromosome number by half, producing four genetically distinct gametes. This process is fundamental to sexual reproduction and genetic diversity.

• Ploidy Change: Meiosis reduces the ploidy level from diploid (2n) to haploid (n), ensuring that offspring have the correct chromosome number after fertilization.

• Genetic Diversity: Crossing over (recombination) during prophase I and independent assortment of chromosomes during metaphase I result in genetically unique daughter cells.

• Example: In humans, meiosis produces gametes with 23 chromosomes, each with a unique combination of alleles.

Mendelian Genetics: Patterns of Inheritance

Mendelian genetics explains how traits are inherited through dominant and recessive alleles. Punnett squares are used to predict genotype and phenotype ratios in offspring.

• Monohybrid Cross: Involves one gene with two alleles. The F2 generation typically shows a 3:1 phenotype ratio (dominant:recessive) and a 1:2:1 genotype ratio (homozygous dominant:heterozygous:homozygous recessive).

• Dihybrid Cross: Involves two genes. The F2 generation shows a 9:3:3:1 phenotype ratio if genes assort independently.

• Punnett Squares: Used to predict offspring ratios and numbers based on parental genotypes.

• Linkage: If genes are linked, dihybrid ratios deviate from 9:3:3:1 due to reduced independent assortment.

Evolutionary Theory and Processes

History of Evolutionary Thought

Evolution is defined as a change in allele frequencies in a population over time. Darwin's theory was influenced by observations of natural variation, fossil records, and the work of earlier scientists.

• Fossils: Preserved remains found in sedimentary rock; dated using relative (stratigraphy) and absolute (radiometric) methods. The fossil record is incomplete due to preservation biases.

• Homology: Similarity due to shared ancestry; relates to synapomorphies and phylogenetic trees. Homology shows evolutionary patterns, while differential fitness (variation in reproductive success) demonstrates evolutionary processes.

• Darwin’s Four Postulates: Variation exists, variation is heritable, more offspring are produced than survive, and survival/reproduction is non-random (fitness differences).

• Natural Selection, Fitness, Adaptation: Natural selection acts on heritable variation, leading to adaptation. Populations with more genetic variation are more likely to adapt to environmental changes.

Evolutionary Processes

Population genetics uses the Hardy-Weinberg principle to study allele and genotype frequencies. Evolutionary mechanisms include selection, drift, gene flow, and mutation.

• Hardy-Weinberg Equilibrium: Predicts genotype frequencies under no evolution. Equations:

$p + q = 1$

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

• Modes of Selection: Directional, stabilizing, disruptive, and balancing selection affect trait distributions.

• Sexual Selection: Selection for traits that increase mating success; may conflict with natural selection.

• Genetic Drift: Random changes in allele frequencies, stronger in small populations; reduces genetic variability.

• Gene Flow: Movement of alleles between populations; can increase or decrease fitness and genetic variability.

Speciation and Phylogeny

Speciation

Speciation is the formation of new species through reproductive isolation. Multiple species concepts exist, each with strengths and limitations.

• Species Concepts: Biological (reproductive isolation), morphological (physical traits), phylogenetic (evolutionary history).

• Allopatric vs. Sympatric Speciation: Allopatric occurs via geographic isolation; sympatric occurs without physical barriers.

• Reproductive Barriers: Prezygotic (before fertilization) and postzygotic (after fertilization) mechanisms prevent gene flow.

Phylogeny and the History of Life

Phylogenies are evolutionary trees constructed using morphological and molecular data. They are hypotheses subject to revision.

• Phylogenetic Trees: Show relationships among taxa; tested with new data. Convergent evolution and trait loss can mislead phylogenies.

• Mass Extinctions: Periods of rapid species loss; often followed by adaptive radiations. The current biodiversity crisis is considered the sixth mass extinction.

Microbial and Eukaryotic Diversity

Bacteria and Archaea

Bacteria and Archaea are prokaryotes with vast diversity, important for ecosystem processes and gene exchange.

• Diversity: Many bacteria were undiscovered until molecular techniques improved.

• Biogeochemical Cycles: Bacteria play key roles in nutrient cycling (e.g., nitrogen fixation).

• Horizontal Gene Transfer: Bacteria can exchange genes across species boundaries.

• Archaea: Distinct from bacteria and eukaryotes; share some features with both.

Protists and Endosymbiosis

Protists are diverse eukaryotes. The endosymbiotic theory explains the origin of mitochondria and chloroplasts.

• Endosymbiotic Events: Mitochondria originated from engulfed proteobacteria; chloroplasts from cyanobacteria. All eukaryotes perform cellular respiration; only some perform photosynthesis.

Plant Diversity and Evolution

Plants are classified into major groups based on evolutionary innovations (synapomorphies).

• Major Groups: Green algae (outgroup), mosses, ferns, gymnosperms, angiosperms.

• Seeds vs. Amniotic Eggs: Both are adaptations for terrestrial life, protecting embryos.

• Ecological Roles: Plants are primary producers, involved in food webs, energy flow, and biogeochemical cycles. They provide ecosystem services and participate in community interactions.

Fungi

Fungi are heterotrophs that decompose organic matter, playing key roles in nutrient cycling and ecosystem functioning.

• Nutrition: Fungi absorb nutrients after external digestion; similar to animals but lack ingestion.

• Ecological Roles: Decomposers, mutualists, pathogens.

• Reproduction: Fungal sexual cycles are complex and differ from animals.

Animal Diversity

Animals are multicellular, heterotrophic organisms with diverse forms and life histories.

• Defining Features: Multicellularity, heterotrophy, movement, specialized tissues.

• Basal Clade: Sponges are considered the most basal animal lineage.

• Chordates and Vertebrates: Chordates include vertebrates; amniotes have amniotic eggs (cf. seeds in plants).

• Human Evolution: Humans are primates, anthropoids, hominids, and hominins. Human evolution is a branching radiation, not a linear progression.

Ecology: Organisms, Populations, and Ecosystems

Introduction to Ecology

Ecology studies interactions between organisms and their environment at multiple scales.

• Range vs. Niche: Range is geographic distribution; niche is the multidimensional set of conditions an organism requires.

• Weather vs. Climate: Weather is short-term atmospheric conditions; climate is long-term patterns. Climate determines biome distribution.

Behavioral Ecology

Behavioral ecology examines the evolutionary basis of animal behavior.

• Ultimate vs. Proximate Causes: Ultimate causes explain why behaviors evolved; proximate causes explain how they occur.

• Altruism and Reciprocity: Altruism reduces individual fitness but benefits others; Hamilton’s rule predicts when altruism evolves ($rB > C$).

Population Ecology

Population ecology studies factors affecting population size and growth.

• Population Growth: Exponential growth occurs without limits; logistic growth includes carrying capacity (K).

• Carrying Capacity (K): Maximum population size an environment can support; affected by density dependence and human activities.

Community Ecology

Community ecology focuses on interactions among species and community structure.

• Species Interactions: Competition, predation, mutualism, commensalism; affect fitness and drive evolution.

• Community Structure: Measured by species diversity, abundance, and composition.

Ecosystem and Global Ecology

Ecosystem ecology examines energy flow and nutrient cycling at large scales.

• Energy Flow: Energy moves through trophic levels; only a fraction is transferred between levels.

• Biogeochemical Cycles: Movement of elements (e.g., carbon, nitrogen) through ecosystems; altered by human activity.

• Climate Change: Driven by increased greenhouse gases; affects ecosystems and evolutionary processes.

• Population Responses: Genetic variability and adaptation determine species' responses to environmental change.

Biodiversity and Conservation Biology

Biodiversity includes genetic, species, and ecosystem diversity. Conservation biology aims to preserve diversity and ecosystem services.

• Components of Diversity: Genetic, species, and ecosystem diversity; each can increase or decrease due to various factors.

• Ecosystem Services: Benefits provided by ecosystems, including food, water, climate regulation, and resilience to disturbance.

Species Interaction	Effect on Species 1	Effect on Species 2	Example
Competition	-	-	Plants competing for light
Predation/Parasitism	+	-	Lion and zebra; tapeworm and human
Mutualism	+	+	Bees and flowering plants
Commensalism	+	0	Barnacles on whales

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