Unit 7: Natural Selection

Evolution

species change over time, give rise to new species, and share a common ancestor

Natural Selection

because resources are limited in nature, organisms w/ heritable traits that favor survival and reproduction will tend to leave more offspring than their peers; causes traits to increase in frequency over generations

Artificial Selection

humans select desirable traits in animals or plants

Genetic Drift

mechanism of evolution in which allele frequencies of a population change over generations due to chance; may result in loss of some alleles and fixation of other alleles

Fitness

measure of how organisms survive and reproduce

Stabilizing Selection

intermediate phenotypes are more fit than extreme ones (will narrow the curve)

Directional Selection

one extreme phenotype is more fit (curve shifts toward favorable phenotype)

Disruptive Selection

both extreme phenotypes are more fit (makes multiple peaks in the curve)

Hardy-Weinberg Equilibrium

when a population is in equilibrium for a gene, it is not evolving and allele frequencies will be the same

What indicates Hardy-Weinberg Equilibrium?

no mutation, random mating, no gene flow/migration, infinite population size, no selection

Mechanisms of Evolution

gene flow, genetic drift, natural selection, mutation, non-random mating

Homologous structures

shared due to ancestry

Analogous structures

shared due to similar selective pressures

Molecular Biology

genes of different organisms are similar

Biogeography

geographical distribution of species

Anatomy

shared anatomical features (some homologous structures seen in embryonic development)

Fossils

confirms existence of extinct species

Vestigial Features

reduced or non-functional version of features

Allopatric Speciation

groups from ancestral population evolve into separate species due to geographical separation

Sympatric Speciation

evolve into separate species without geographic separation