Revised Midterm 1 biol 213

Abiogenesis

The creation of organic molecules (amino acids, nitrogenous bases) from abiotic materials.

Recipe for Life on Earth

1. Creation of organic molecules -> 2. Molecules join into macromolecules -> 3. Formation of protocells -> 4. Self-replicating molecules (inheritance).

Protocells

Membrane-bound droplets (like liposomes) maintaining an internal chemical environment distinct from their surroundings.

Miller-Urey Experiment (1953)

Demonstrated abiogenesis by showing spontaneous production of amino acids/organic molecules from inorganic compounds under early-Earth conditions.

Panspermia Hypothesis

The theory that life originated elsewhere in the universe and was delivered to Earth via meteorites.

Murchison Meteorite Evidence

A 4.56-billion-year-old rock found in Australia containing lipids, 90+ amino acids, and nitrogenous bases (uracil, xanthine).

RNA World Hypothesis

The hypothesis that RNA was the first genetic and catalytic molecule before DNA and proteins evolved.

Ribozymes

RNA molecules capable of acting as biological catalysts for chemical reactions.

LUCA

Last Universal Common Ancestor; the most recent common ancestor from which all current life on Earth descends.

Earliest Evidence of Life

Arose ~3.5–4.1 Ga (billion years ago) in the oceans; organisms were anaerobic prokaryotes.

Great Oxidation Event

Occurred ~2.4–2.1 Ga when photosynthesizing cyanobacteria evolved, enriching the atmosphere with oxygen and selecting for aerobic organisms.

Cambrian Explosion

The rapid appearance (~541–520 Ma) of most major animal body plans/phyla in the fossil record.

Mass Extinctions ("Big Five")

Extinction events killing massive percentages of species, leaving empty ecological niches that trigger rapid diversification/adaptive radiation of surviving lineages.

Evolution Timeline: Rise of Complex Life

1. Great Oxidation Event (~2.4 Ga) -> 2. Eukaryotes (~2.0 Ga) -> 3. Multicellular Algae (~1.2 Ga) -> 4. Animals (~800–600 Ma) -> 5. Cambrian Explosion (~541 Ma).

Evolution Timeline: Colonization of Land

1. Land Plants (~470 Ma) -> 2. Land Arthropods (~430 Ma) -> 3. Land Vertebrates/Tetrapods (~370 Ma) -> 4. Amniotic Egg (~320 Ma).

Evolution Timeline: Emergence of Humans

Anatomically modern humans (Homo sapiens) emerged ~300,000 years ago, representing recent evolutionary history.

Evolution (Biological)

The change in allele frequencies within a population over successive generations.

Individuals vs. Populations in Evolution

Selection acts on INDIVIDUALS (their phenotype determines survival/reproduction), but evolution occurs in POPULATIONS (allele frequency changes over generations).

Phenotypic Trait vs. Allele

A phenotypic trait is an observable characteristic; an allele is a specific genetic variant coding for traits.

Special Creation Theory

17th-century European belief that species were created recently, independently, and remain fixed/unchanging through time.

Georges Cuvier

Father of paleontology; documented species extinction through fossil layers.

Uniformitarianism (Hutton & Lyell)

Geological principle stating the same physical processes shaping Earth today operated in the past.

Lamarckian Transmutation

Flawed theory that traits acquired during an organism's lifetime through use/disuse are passed to offspring.

Thomas Malthus' Population Principle

Observation that populations grow exponentially while food supply grows linearly, creating fierce competition for survival.

Darwin's "Descent with Modification"

Principle that all living species originated and diversified from shared common ancestors.

Natural Selection

The non-random process where individuals with favorable heritable traits survive and reproduce at higher rates.

Three Conditions for Natural Selection

1. Phenotypic Variation in a population. 2. Heritability (variation must be genetic). 3. Differential Fitness (trait affects survival/reproduction).

Biological Fitness

An individual's relative reproductive success (contribution of alleles to the next generation's gene pool).

Four Lines of Evidence for Evolution

1. Paleontological (fossils, transitional forms). 2. Anatomical/Developmental Homology. 3. Molecular Homology. 4. Direct Observation.

Paleontological Evidence

Fossils showing extinct organisms, ancient dates of life, and transitional forms (e.g., feathered dinosaurs bridging reptiles and birds).

Homology

A structural, developmental, or molecular similarity in different species inherited from a common ancestor.

Molecular Homology

Universal genetic code (DNA/RNA, triplet codons, central dogma) shared across all life on Earth.

Direct Observational Evidence

Real-time tracking of evolutionary changes (e.g., antibiotic resistance, lab bacterial evolution, artificial selection in agriculture).

Artificial Selection

Human-driven selective breeding for desired traits over generations (e.g., crops, dog breeds).

Worldview vs. Knowledge System

A worldview is a fundamental framework of beliefs/assumptions through which reality is perceived; a knowledge system is a structured, shared way of producing/transmitting knowledge influenced by worldviews.

The Core Evolutionary Cycle

Phenotypic variation drives selection, leading to differential survival/reproduction, but requires heritable transmission of traits across generations.

Darwin's "Blind Spot"

Darwin established natural selection but did not know the underlying physical mechanisms of heritable transmission (genes and DNA).

Blending Inheritance Hypothesis

1800s idea that offspring inherit traits as a literal blend of parents; flawed because it incorrectly predicts phenotypic variation would disappear over time.

Lamarckian Inheritance (Acquired Characteristics)

Flawed theory that traits acquired during an organism's lifetime are physically passed to offspring.

Gregor Mendel's Contribution

Provided quantitative evidence for a particulate mechanism of inheritance through controlled pea plant breeding experiments.

Why Pea Plants Were Ideal Model Organisms

Categorizable traits, easily controlled cross/self-pollination, short generation time, and high offspring numbers.

P, F1, and F2 Generations

P = true-breeding parental generation; F1 = hybrid offspring of P generation; F2 = self/cross-pollinated offspring of F1 generation.

Mendel's Monohybrid Cross Results

Crossing true-breeding purple x white plants yielded 100% purple in F1, and a ~3:1 ratio (purple:white) in F2, showing recessive traits are masked, not destroyed.

Gene vs. Allele

A gene is a region of DNA governing a specific character; an allele is an alternative structural version/variant of that gene.

Phenotype vs. Genotype

Phenotype is the observable physical or physiological trait; genotype is the underlying genetic/allelic composition.

Homozygous vs. Heterozygous

Homozygous organisms have two identical alleles at a locus (true-breeding); heterozygous organisms have two different alleles.

Dominant vs. Recessive Alleles

Dominant alleles express fully in heterozygotes (often active functional proteins); recessive alleles are masked in heterozygotes (often non-functional/mutated proteins).

Common Dominance Misconception

Dominance does NOT mean an allele is fitter, healthier, or more common in a population; allele frequency is determined by selection, not dominance status.

Mendel's Law of Segregation

The two alleles for a single gene separate randomly during gamete formation so that each gamete receives only one allele.

Cellular Mechanism of Segregation

The separation of homologous chromosome pairs moving to opposite poles during Anaphase I of meiosis.

Punnett Square Ratios (Heterozygous Monohybrid Cross)

A cross of Pp x Pp yields a 3:1 Phenotypic ratio (Dominant:Recessive) and a 1:2:1 Genotypic ratio (1 PP : 2 Pp : 1 pp).

Product Rule of Probability

Used for independent events occurring simultaneously (Event A AND Event B): multiply their individual probabilities together.

Sum Rule of Probability

Used for mutually exclusive alternative outcomes (Event A OR Event B): add their individual probabilities together.

Test Cross

Breeding an individual of unknown genotype (showing dominant phenotype) with a known homozygous recessive individual to determine the mystery genotype.

Interpreting Test Cross Results

If 100% of offspring show dominant phenotype, the parent is homozygous dominant; if a 1:1 ratio appears, the parent is heterozygous.

Chromosomal Theory of Inheritance

Proposed by Walter Sutton (1903); states that genes are located on chromosomes, and homologous chromosomes segregate independently during meiosis.

Complete Dominance

The heterozygous phenotype is completely indistinguishable from the homozygous dominant phenotype.

Incomplete Dominance

The heterozygous phenotype appears as an intermediate "blend" between the two homozygous parental phenotypes (e.g., pink flowers from red and white parents).

Codominance

Both alleles are fully and simultaneously expressed in the heterozygote in distinct, distinguishable ways (e.g., AB blood type).

Multiple Alleles

When a single gene locus has three or more potential allele variants within a population (e.g., human ABO blood groups: IA, IB, i).

Polygenic Inheritance

An additive effect where two or more distinct genes collectively influence a single continuous phenotypic trait (e.g., skin color, height).

Pleiotropy

When a single gene mutation influences multiple, seemingly unrelated phenotypic traits (e.g., Sickle Cell Disease causing anemia, organ damage, and pain).

Biological Population

A group of individuals of the same species occupying the same geographical area that actively interbreed with one another.

Individual vs. Population Cross

Individual Punnett squares use gamete probabilities (1/2, 1/2) for single matings; Population crosses use whole allele frequencies (e.g., p, q) to calculate total population genotype frequencies.

Genotype Frequency

The relative proportion or abundance of a specific genotype in a population; Formula: f(BB) = (Number of BB individuals) / (Total individuals).

Allele Frequency

The relative proportion of a specific allele at a genetic locus in a population; Formula: f(B) = (Number of B alleles) / (Total alleles in population).

Calculating Allele Frequencies from Genotype Frequencies

For a diploid population with two alleles: f(B) = f(BB) + 1/2 f(Bb) and f(b) = f(bb) + 1/2 f(Bb).

Genetic Variation

The presence of differences in sequences of genes between individual organisms of a species; the mandatory raw material required for evolution.

Mutations (e.g., SNPs)

The ultimate source of all novel genetic variation, introducing changes such as Single Nucleotide Polymorphisms (SNPs), insertions, or deletions.

Four Mechanisms of Evolution

1. Selection; 2. Migration (gene flow); 3. Genetic drift (random sampling changes); 4. Mutation.

Hardy-Weinberg Equilibrium (HWE)

The null hypothesis model stating that allele and genotype frequencies remain constant across generations in the absence of evolutionary forces.

Five Assumptions of Hardy-Weinberg Equilibrium

1. No mutation; 2. No gene flow/migration; 3. Infinitely large population (no genetic drift); 4. No natural selection; 5. Random mating.

Hardy-Weinberg Equations

Allele frequencies: p + q = 1; Genotype frequencies: p² + 2pq + q² = 1 (where p = f(A), q = f(a), p² = f(AA), 2pq = f(Aa), q² = f(aa)).

Why Hardy-Weinberg is Useful

It serves as a baseline null hypothesis to test whether natural selection or other evolutionary forces are actively acting on a specific gene locus.

Steps to Test if a Population is in HWE

1. Calculate observed genotype frequencies; 2. Calculate allele frequencies (p and q); 3. Calculate expected genotype frequencies (p², 2pq, q²); 4. Compare observed vs. expected.

Interpretation of HWE Violation

If observed genotype frequencies significantly deviate from expected values (p², 2pq, q²), at least one assumption is violated and the population is evolving at that locus.

Traditional Ecological Knowledge (TEK) & Population Genetics

Yurok Tribe TEK identified spring and fall Chinook salmon as distinct populations; genetic studies confirmed distinct allele differences at the GREB1L gene.