Unit 7: Natural Selection & Evolution

Evolution

Change in allele frequencies in a population over time

Natural Selection

Process where individuals with advantageous traits survive and reproduce more successfully than others

Fitness

Ability of an organism to survive and produce fertile offspring in a given environment

Adaptation

Inherited trait that increases an organism’s survival and reproductive success

Descent with Modification

Darwin’s idea that species change over time and share common ancestors

Population

Group of individuals of the same species living in the same area that interbreed

Species

Group of organisms that can interbreed and produce fertile offspring

Gene Pool

All the alleles present in a population

Allele Frequency

Proportion of a specific allele in a population

Genetic Variation

Differences in DNA among individuals in a population

Mutation

Random change in DNA that creates new genetic variation

Recombination

Shuffling of alleles during meiosis that increases genetic variation

Crossing Over

Exchange of genetic material between homologous chromosomes during prophase I of meiosis

Independent Assortment

Random distribution of homologous chromosomes during meiosis I

Random Fertilization

Random combination of sperm and egg during reproduction

Hardy-Weinberg Equilibrium

Theoretical condition where allele frequencies do not change over time, meaning evolution is not occurring

Hardy-Weinberg Equation

p² + 2pq + q² = 1 used to calculate genotype frequencies in a population

p (Allele Frequency)

Frequency of the dominant allele in a population

q (Allele Frequency)

Frequency of the recessive allele in a population

Directional Selection

Selection where one extreme phenotype is favored, shifting population traits in one direction

Stabilizing Selection

Selection where intermediate phenotypes are favored and extremes are selected against

Disruptive Selection

Selection where both extreme phenotypes are favored over intermediates

Genetic Drift

Random change in allele frequencies due to chance events, especially in small populations

Bottleneck Effect

Sharp reduction in population size that reduces genetic diversity due to a random event

Founder Effect

Loss of genetic variation when a small group starts a new population

Gene Flow

Movement of alleles between populations through migration

Speciation

Formation of new species through evolutionary processes

Reproductive Isolation

Mechanisms that prevent species from interbreeding

Prezygotic Barrier

Barrier that prevents fertilization before a zygote forms

Postzygotic Barrier

Barrier that occurs after fertilization, reducing viability or fertility of offspring

Allopatric Speciation

Speciation caused by geographic isolation of populations

Sympatric Speciation

Speciation without geographic isolation, often due to genetic or behavioral differences

Phylogenetic Tree

Diagram showing evolutionary relationships among species based on common ancestry

Cladogram

Branching diagram showing relationships based on shared derived characteristics

Common Ancestry

Shared evolutionary origin of different species

Homologous Structures

Structures with similar evolutionary origin but different functions

Analogous Structures

Structures with similar function but different evolutionary origins

Vestigial Structures

Reduced or nonfunctional structures inherited from ancestors

Endosymbiotic Theory

Theory that mitochondria and chloroplasts originated from free-living prokaryotes engulfed by early eukaryotic cells