AP Biology Unit 7: Natural Selection

AP Biology Unit 7 study guide.

Natural Selection

The process by which organisms with heritable traits are better suited to their environment tend to survive and reproduce at higher rates than individuals without those traits.

Adaptation

An inherited characteristic that enhances an organism’s survival and reproduction in a specific environment. Adaptations arise through natural selection.

Fitness

The ability of an individual to survive and reproduce in its specific environment. It’s often measured by the number of offspring an individual produces that survive to reproduce themselves.

Selective Pressure

Any factor in the environment that can influence the survival and reproduction of individuals in a population.

Examples: Predators, competition for resources, and climate change

Variation

Differences in heritable traits among individuals in a population. This variation is a major criteria for natural selection.

Heritability

The ability of a trait to be passed down from parents to offspring. Only heritable traits can be acted upon by natural selection.

Overproduction

The tendency of a species to produce more offspring than the environment can support. This leads to competition for resources.

Directional Selection

Type of natural selection in which individuals at one extreme end of the phenotype range survive or reproduce more successfully than other individuals.

Stabilizing Selection

Type of natural selection in which intermediate phenotypes survive or reproduce more successfully than individuals at either extremes (Reduces variation)

Disruptive Selection

Type of natural selection in which individuals at both extreme ends of the phenotypic range survive or reproduce more successfully than individuals with intermediate phenotypes.

Artificial Selection

The selection where humans have involvement in the breeding of plants or animals, breeding for specific traits.

Gene Pool

The total collection of genes in a population at any one time. Consists of all the alleles for all the individuals of the population.

Gene Frequency

The proportion of a specific allele within a population’s gene pool. Natural selections can cause changes in the allele frequencies over time.

Hardy-Weinberg Equilibrium

The frequencies of alleles and genotypes in a population will remain constant from generation to generation in the absence of evolutionary influences (No mutations, random mating, no gene flow, no genetic drift, and no natural selection).

Genetic Drift

Fluctuations in allele frequencies from one generation to the next, especially in smaller populations. (Loss of genetic variation)

Bottleneck Effect

Sudden decrease in a population size due to a chance event.

Founder effect

New population with a small number of individuals who moves away from a larger population

Gene Flow

The transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes. Gene flow can alter allele frequencies and reduce genetic differences.

Mutation

A change in the nucleotide sequence of an organism’s DNA. Mutations are a source of new genetic variation. Some can be neutral, harmful, or beneficial.

Evolutionary Fitness

The contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals. Reproductive success

Convergent Evolution

The independent evolution of similar features in different lineages. This occurs when different organisms face similar environmental pressures and natural selection favors similar adaptations.

Analogous Structures

Structures in different species that have similar functions but have evolved separately, thus do not share a common ancestral origin. Result of convergent evolution.

Homologous Structures

Structures in different species that are similar because of common ancestry, even if they have different functions.

Vestigial Structures

Features that served a function in the organisms ancestors but have lost most or all of their original function in modern species