Unit 7: Natural Selection & Evolution

Vocabulary flashcards covering the major terms and concepts from Unit 7 (Natural Selection and Evolution) to aid AP Biology study and exam preparation.

Natural Selection

A mechanism of evolution where individuals with favorable heritable traits survive and reproduce more successfully, passing those traits to the next generation.

Evolutionary Fitness

The relative reproductive success of an individual; measured by the number of viable, fertile offspring produced.

Phenotypic Variation

Differences in physical traits among individuals of a population on which natural selection can act.

Selective Pressure

An environmental factor (biotic or abiotic) that influences differential survival and reproduction within a population.

Artificial Selection

The human-directed breeding of organisms to enhance desired traits and reduce undesired ones.

Convergent Evolution

Independent evolution of similar adaptations in distantly related organisms exposed to similar selective pressures.

Mutation

Random change in DNA sequence that introduces new genetic variation into a population.

Genetic Drift

Random fluctuations in allele frequencies, especially significant in small populations.

Bottleneck Effect

Genetic drift resulting from a drastic reduction in population size, leaving a small, less-diverse gene pool.

Founder Effect

Loss of genetic variation when a new population is established by a small number of individuals from a larger population.

Gene Flow (Migration)

Movement of alleles between populations through the migration of individuals or gametes.

Population Genetics

The study of allele and genotype frequency distribution and change under the influence of evolutionary processes.

Hardy-Weinberg Equilibrium

Mathematical model stating that allele and genotype frequencies remain constant from generation to generation in an ideal, nonevolving population.

Allele Frequency

Proportion of a specific allele among all alleles for a given gene in a population (p or q in Hardy-Weinberg).

Genotype Frequency

Proportion of a given genotype (e.g., p², 2pq, q²) within a population.

Null Hypothesis (in evolution studies)

The prediction that no evolutionary change (e.g., no difference between observed and expected allele frequencies) has occurred.

Chi-Square Test

Statistical test used to compare observed data with data expected under a specific hypothesis, often Hardy-Weinberg.

Evidence for Evolution

Data from fossils, morphology, biochemistry, genetics, geography, and mathematics supporting evolutionary change.

Fossil Record

Chronological collection of preserved remains providing evidence of past life and evolutionary transitions.

Morphological Homology

Similar body structures in different species due to common ancestry.

Vestigial Structure

Remnant structure with little or no current function that was functional in ancestors (e.g., human appendix).

Molecular Clock

Technique that uses mutation rates in DNA to estimate the time since two species diverged.

Phylogenetic Tree

Diagram showing evolutionary relationships among species, often calibrated to time.

Cladogram

Branching diagram illustrating evolutionary relationships based on shared derived characters, without time scale.

Common Ancestry

Concept that different species share ancestors at some point in evolutionary history.

Continuing Evolution

Ongoing genetic change in populations, evidenced by phenomena such as antibiotic resistance and genomic shifts.

Antibiotic Resistance

Evolved ability of microorganisms to withstand antimicrobial drugs, exemplifying rapid evolution.

Adaptive Radiation

Rapid evolutionary diversification of a lineage into many niches, often after environmental change or mass extinction.

Punctuated Equilibrium

Evolutionary model proposing rapid bursts of change followed by long periods of stasis.

Gradualism

Evolutionary model proposing slow, continuous change over long periods.

Speciation

Formation of new species when populations become reproductively isolated and diverge genetically.

Reproductive Isolation

Barriers preventing gene flow between populations, leading to speciation.

Prezygotic Barrier

Reproductive isolation mechanism that prevents fertilization (e.g., temporal, behavioral, mechanical).

Postzygotic Barrier

Isolation mechanism acting after fertilization, producing inviable or sterile hybrids.

Allopatric Speciation

Speciation that occurs when populations are geographically separated.

Sympatric Speciation

Speciation occurring within the same geographic area, often through polyploidy or niche partitioning.

Extinction

Complete loss of a species when the last individual dies.

Genetic Diversity

Total number of genetic characteristics in the genetic makeup of a species; enhances adaptability to environmental change.

Hardy-Weinberg Conditions

Large population, no migration, no mutation, random mating, and no natural selection—requirements for equilibrium.

Differential Survival

Variation in survival rates among individuals due to trait differences; core of natural selection.

RNA World Hypothesis

Proposal that self-replicating RNA molecules were precursors to current life, serving as both genetic material and catalyst.

Origin of Life (Abiogenesis)

Hypothesized process by which life arose from nonliving matter on early Earth, supported by geological and chemical evidence.