Theory of Natural Selection 10.3 pg. 304

Artificial Selection Where humans change a species by breeding it for certain traits. Ex. Humans select traits that are favorable in plants and animals, then breed only those with the trait, producing more of that trait.

Heritability The ability of a trait to be passed down from one generation to the next.

Struggle for survival Resources are limited in a population, limiting population growth. Food, water, shelter, disease limit population growth Population – individuals of the same species that live in an area

Natural Selection Mechanism where individuals that have inherited beneficial adaptations produce more offspring than other individuals. Nature is the selecting agent

Four main principles of natural selection 1. Variation 2. Overproduction 3. Adaptation 4. Descent with modification

Variation Heritable differences result from differences in the genetic material of an organism Could be inherited from parent or the result of a mutation

Overproduction Having more offspring raises the chance that some will survive, but it also results in more competition for resources

Adaptation A certain variation may allow an individual to survive better than other individuals. More successful individuals are “naturally selected” to live longer and produce more offspring.

Decent with modification Over time, more individuals will have the favorable trait in every following generation, as long as environmental conditions stay the same.

Fitness Fitness - The measure of the ability to survive and produce more offspring relative to other members of that population.

Genetic Variation within Populations 11.1 pg. 329

Genetic Variation Why its beneficial… A population with a lot of genetic variation has a wide range of phenotypes. A wide range of phenotypes means some individuals can adapt with a changing environment and survive.

Genetic Variation How its stored in a population… Stored in a gene pool The combined alleles of all individuals in a population

Genetic Variation How it’s measured… Measured by allele frequency How common an allele is in a population

Mutations Random change in DNA of a gene This can form a new allele, which can be passed to offspring if in a reproductive cell, increasing the variation in a gene pool

Recombination Happens when new allele combinations form in offspring. Happens during meiosis

Natural Selection in Populations 11.2

Normal Distribution Frequency is highest in the middle (mean) and decreases towards the extreme ends. A population follows a normal distribution when: all phenotypes provide an equal chance of survival

Microevolution Microevolution - a change observed in allele frequency in a population over time. Microevolution occurs on a small scale.

Directional Selection Selection that favors phenotypes at one extreme Example: Drug resistant bacteria

Stabilizing Selection Selection that favors the intermediate phenotype, it is most common Example: Wasps

Disruptive Selection Selection that favors both extremes Example: Buntings (species of bird)

Other Mechanisms of Evolution 11.3 pg. 335

Gene Flow Definition: movement of alleles from one population to another How it works: occurs when individuals move between populations

Gene Flow Lots of gene flow between populations  Increases genetic variation of receiving population & keeps gene pools similar Limited gene flow between populations  Two populations become more genetically different. Species could possibly evolve into two different species.

Genetic Drift Definition: Change in allele frequencies due to chance. How it works: causes loss of genetic diversity in a population.

Genetic Drift Key Terms Bottleneck Effect: occurs after an event greatly reduces the size of a population

Genetic Drift Key Terms Founder Effect: occurs after a small number of individuals colonize a new area.

Genetic Drift Negative Effects… Population losses genetic variation Population is less likely to have individuals that can adapt to survive in changing environment Lethal alleles carried by heterozygous individuals will become more common due to chance.

Sexual Selection Definition: occurs when certain traits increase mating success. How it works: Females are choosy about mates, forcing mates to have certain traits that will increase their mating success.

Sexual Selection Types Intrasexual: involves competition among males; whoever wins, wins the female. Bighorn sheep butting heads Intersexual: males display certain traits that will attract the female Peacocks fanning tails Frigate Birds

Speciation Through Isolation 11.5

Reproductive Isolation Occurs when members of a population can no longer mate with each other This is the final step in speciation…

speciation The rise of 2 or more species from 1 species. (splitting of species into different species). There are 3 reasons for speciation…

1. Behavioral Isolation Behavioral Isolation is caused by differences in… Mating rituals Chemical signals Courtship songs/dances

2. Geographic Isolation Geographic Isolation is caused by… Physical separation Distance between populations

3. Temporal Isolation Temporal Isolation exists when… Timing of mating rituals is off Timing can change because of seasons, weather, time of day, etc.

Patterns in Evolution 11.6 pg. 347

Convergent Evolution Evolution towards similar characteristics in unrelated species Ex. Birds and insects with wings Ex. Fins of sharks and dolphins

Divergent Evolution When closely related species evolve in different directions and become increasingly different. Due to different environments Ex. Kit Fox and Red Fox

Coevolution Process in which two or more species evolve in response to changes in each other.

Coevolution Beneficial Relationships: Acacia plant and ants. Ants will hide in plants hollow holes and sting potential predators.

Coevolution Evolutionary Arms Races: species respond to pressure from the other through better adaptations over generations.

Extinction Elimination of a whole species from Earth. Ex - Tasmanian tiger—known as a thylacine

Extinction Background Extinction: Occur continuously at a slow rate; part of the cycle of life. Mass Extinction: Rare; operate at a global level, occurring suddenly due to a catastrophic event.

Patterns in Speciation Punctuated Equilibrium: speciation occurs suddenly, not gradually and are followed by long periods of little evolutionary change.

Patterns in Speciation Adaptive Radiation: diversification of one ancestral species in to many descent species (usually over a wide range of environments)