Khan Academy Unit #7- Natural selection

Flashcards on Natural Selection, Evolution, and Speciation

Evolution

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

Natural Selection

Because resources are limited in nature, organisms with heritable traits that favor survival and reproduction will tend to leave more offspring than their peers, causing traits to increase in frequency over generations.

Artificial Selection

Humans select desirable traits in animals or plants, for example, domestication of wolves.

Genetic Drift

A mechanism of evolution in which allele frequencies of a population change over generations due to chance, and its effects on small populations are strongest.

Natural Selection in Populations

Natural selection acts on phenotype to cause microevolution in a population.

Fitness

Measure of how organisms survive and reproduce.

Stabilizing Selection

Intermediate phenotypes are more fit than extreme ones; narrows the curve.

Directional Selection

One extreme phenotype is more fit.

Disruptive Selection

Both extreme phenotypes are more fit; makes multiple peaks in the curve.

Hardy-Weinberg Equilibrium

When a population is not evolving and allele frequencies will be the same.

Mechanisms of Evolution

Gene flow, genetic drift, natural selection, mutation, non-random mating.

Evidence for Evolution

Similar anatomy may be homologous or analogous; genes of different organisms.

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.

Phylogenetic Trees

A diagram that shows the evolutionary relationships among organisms; species are more related if they have a more recent common ancestor.

Speciation

Process by which new species form; a group in a species becomes reproductively isolated.

Allopatric Speciation

Groups from ancestral population evolve into separate species due to geographical separation.

Sympatric Speciation

Evolve into separate species without geographic separation.

Prezygotic Isolation

Habitat isolation, temporal isolation, behavioral isolation, gametic isolation, mechanical isolation.

Postzygotic Barriers

Sickly offspring, sterile offspring (ex: mule).