Comprehensive Lecture Notes on Adaptation, Natural Selection, and Evolutionary Genetics

Evolution

A change in inherited characteristics, measured through allele frequencies in a population, across generations.

Natural Selection

A process wehre individuals with advantageous inherited traits survive and reproduce more successfully, making those traits more common

Adaptation

A inherited characteristic that increases reproductive success in a particular environment

Fitness

An organisms relative reproductive success, or contribution to future generations

Genetic Variation

Inherited differences among individuals within a population

Variation due to genetics

within a population there are differences and many of these differences are due to genetics

Overproduction

Producing more offspring than can survive in the environment

Struggle for existence

Competition and environmental challenges that limit survival and reproduction

Differential reproductive success

those individuals with the better characteristics have the greater ability to survive and contribute offspring (fitness). As a result the composition of the population in the next generation changes.

Heritability (H²)

The proportion of variation in a trait within a population attributable to genetic differences, under the conditions studied..

Microevolution

Changes in allele frequencies within a population across generations

Macroevolution

Large-scale evolutionary patterns, including speciation and diversification of lineages.

Scientific theory

A well-supported explanation of natural phenomena based on extensive evidence.

Directional Selection

Natural selection that favors one extreme phenotype, shifting the populations average toward that extreme

Stabilizing selection

Natural selection that favors intermediate phenotypes, and selects against both extremes. (ex:birth weight in humans )

Disruptive selection

Natural selection that favors extreme phenotypes over intermediate ones, leading to two or more contrasting phenotypes in a population.

Polymorphism

The presence of two or more distinct forms of a characteristic within a population.

Artifical selection

Human-directed breeding that favors particular inherited characteristics

Sexual selection

Selection for traits that increase mating success through preference for certain characteristics by one sex. (results in sexual dimorphism)

Sexual dimorphism

Differences in physical characteristics between males and females of a species.

Gradualism

The idea the evolutionary change accumulates through small changes over long periods.

Punctuated equilibrium

An evolutionary pattern with long periods of little change interrupted by relatively rapid evolutionary change.

Stasis

A period in which little or no evolutionary change occurs in a species, often seen in the context of punctuated equilibrium.

Population genetics

The study of the frequency of alleles in a population over generations

Gene pool

the sun of all copies of allen’s at all loci in a population

Gene

A unit of hereditary information located in DNA

Allele

An alternative version of a gene

Locus (plural:loci)

A specific location on a chromosome

Genotype

an individuals genetic make up, such as AA, Aa, or aa

Phenotype

An observable characteristic influenced by genotype and the environment.

Homozygous

Having two idential alleles on a gene locus, such as AA or aa

Heterozygous

Having two different alleles at a gene locus, such as Aa.

Dominant allele

An allele that can determine a trait in a heterozygote under complete dominance.

Recessive allele

an allele whos effect is masked in a herterozygote under complete dominance

Hardy-Weinberg equilibrium

A population genetics model in which allele and genotype frequencies remain stable across generations under specified assumptions including no selection, mutation, migration, or genetic drift.

Hardy Weinberg Principle

Assumes random mating, no selection, large population, no migration or gene flow, no mutations

Allele frequency

The proportion of all copies of a gene represented by a particular allele

Genotype frequency

the proportion of individuals in a population with a particular genotype

Central Dogma

The general flow of genetic information from DNA to RNA to protein.

Mutation

A change in DNA sequence that can create a new allele. Ultimate source of variation.

Gene flow

movement of alleles between populations throguh migration and reproduction

Genetic drift

happens when allele frequencies change by chance rather than because a trait improves survival or reproduction. It is especially important in small populations.

Bottleneck effect

A population suddenly becomes much smaller because of a random event. The survivors may have different allele frequencies from the original population. Can reduce genetic variation

Founder effect

Genetic drift that occurs when a few individuals establish a new population, leading to a loss of genetic variation.

Nonrandom mating

Mating in which individuals do not pair randomly with resepct to particular traits or relationships

Assortive mating

Individuals preferentially mating with others that share particular characteristics (not by random chance)

Inbreeding

Reproduction between genetically related individuals

Inbreeding depression

Reduced fitness that can result from increased homozygosity and expression of harmful recessive alleles.

Independent assortment

Random orientation and separation of homologous chromosome pairs during meiosis, creating different chromosome combinations.

Crossing over

Exchange of DNA segments between homologous chromosomes during meiosis

Syngamy

the fusion of gametes during fertilization

Blending inheritance

An outdated theory that parental hereditary characteristics permanently mix together.

Modern synthesis

The integration of Darwinian natural selection with Mendelian genetics and population genetics.

Limiting factor

An environmental condition that restricts the growth, abundance, or distribution of an organism.

Range of tolerance

the range of conditions an organism can survive, with an potimum where performance is highest

Acclimation

The physiological adjustment of an organism to environmental changes, enhancing its ability to survive under varying conditions.

Phenotypic plasticity

The ability of an organism to change its phenotype in response to changes in the environment, allowing it to adapt and survive under different conditions.

Cline

A gradual change in a trait or allele frequency across a geographic or environmental gradient

Ecotype

A genetically distinct population of a species adapted to specific environmental conditions, often resulting in variations in phenotype and behavior.

Common garden experiment

A study that grows organisms from different populations under the same conditions to help identify genetic influences on their traits.

Trade-off

A situation where an advantage under one condition comes with a disadvantage under another.

Generalist

An organism that can use a relatively wide range of resources or environmental conditions.

Specialist

An organism adapted to a narrower range of resources or environmental conditions.

Niche

The ecological role and range of an organism within its environment, including its habitat, resource use, and interactions with other species.

Speciation

The evolutionary process through which new species arise.

Reproductive isolation

Barriers that prevent or limit successful gene exchange between populations

Allopatric speciation

Speciation resulting from divergence after geographic separation

Sympatric speciation

Speciation that develops in the same geographic area without a physical geographic barrier

Parapatric speciation

Speciation between neighboring populations that diverge despite limited gene flow.

Peripatric speciation

Speciation involving an isolated small population at the edge of a larger ancestral population.

Subspecies

Distinct populations within one species that show inherited differences, often associated with geographic separation.

Reproductive isolation mechanisms

Barriers that restrict or prevent successful reproduction and gene exchange between populations

Adaptive radiation

The diversification of an ancestral lineage into multiple forms adapted to different ecological opportunities.

Geographic Isolation

Physical seperation of populations that restric gene flow

Morphological species

species identified mainly through physical characteristics.

Biological species

Groups of organisms that actually or potentially interbreed and are reproductively isolated from other groups.

Ring species

A series of neighboring populations that can interbreed locally, while some populations at opposite ends are reproductively isolated.

Ecological species

Species distinguesed by their ecological niches

Biochemical species concept

Classifying species using biochemical or molecular differences.

Evoluationary species concept

Defining a species as a distinct evolutionary lineage with its own history.

Fact

A statement that can be verified as true or false based on evidence.

Theory

A well-substantiated explanation of some aspect of the natural world, based on a body of evidence and testable hypotheses.

hypothesis

A proposed explanation for a phenomenon based on limited evidence, subject to further testing and validation.

polymorphic populations

populations containing multiple distinct forms of a trait

blending theory

The outdated idea that inherited characteristics permanently blend together in offspring.

environmental tolerance

the range of environmental conditions an organism can tolerate

law of limits

too much or too little of an environmental factor can restrict population size

Quantitative traits

Characteristics that vary in amount or degree such as body size or beach depth