Natural and Artificial Selection Notes

Variation within species: Genes cause variation within the same species. A litter of puppies can have different fur colors and patterns because they inherit a different combination of alleles from their parents.
Mutations: Mutations are another source of genetic variation and are a permanent change in the genetic material of an organism. They can occur during DNA replication.
Effects of mutations:
- Harmful mutations can cause a cell to die, malfunction, or multiply uncontrollably. Examples include cancer and sickle cell anemia.
- Beneficial mutations provide an advantage. An example includes a small town in Italy that won’t get atherosclerosis
- Neutral mutations have no effect. An example includes people with webbed hands or feet.

Selective advantage: Some mutations may provide a selective advantage in changing conditions. A selective advantage is a genetic advantage that improves an organism’s chance of survival, usually in a changing environment.
Natural selection: Natural selection is the process by which characteristics of a population change over many generations as organisms with heritable traits survive and reproduce, passing their traits to offspring. Genetic variation within a species is necessary for natural selection to occur.
Adaptation: An adaptation is a structural, behavioral, or physiological feature that improves an organism’s chance of survival in its environment to reproduce. For example, cacti have large stems to store water.
Advantageous mutations: Organisms with advantageous mutations may survive better in a changing environment.
Abiotic factors: An abiotic factor selects for certain characteristics in some individuals and against other characteristics.
Population changes: Over time, the population changes because individuals with favorable characteristics survive and reproduce.
Selective pressures: The environment exerts selective pressures that result from predators, parasites, and competition for limited resources.

Situational natural selection: Natural selection is situational and doesn’t anticipate changes in the environment. A trait that may be a disadvantage to an individual at one time may be advantageous to its survival later. Alleles for this trait will be passed on to the next generation of offspring.
Speciation: Individuals of the same species can interbreed to produce fertile offspring. Sometimes members of a population change so much that they are no longer able to produce fertile offspring with members of the original population, leading to speciation, where new species are formed.
Adaptive radiation: Geographic barriers can isolate a population, resulting in new species that are unable to interbreed. Examples of geographic barriers include glaciers, bodies of water, lava flows, mountains, and islands.
Diversification: Adaptive radiation is the diversification of a common ancestral species into a variety of differently adapted species. Finches on the Galapagos Islands have different beak shapes due to their diverse diets.
Galapagos species: Tortoises on the Galapagos Islands are all different due to mutations, natural selection, and adaptive radiation.
Extinction: Extinction occurs when a species completely disappears from Earth. Mass extinctions result in a decline in the number of species.

DNA mutations produce genetic diversity within a population.
Natural selection favors traits that make an organism better suited to its environment.
Natural selection can lead to the formation of new species.