Unit 7: Natural Selection

LaMarck theory

If an organism changes during life in order to adapt to its environment, those changes are passed on to its offspring.

Evolution through use and disuse. Inheritance of acquired characteristics.

Fitness

Ability to contribute genes to the next generation (reproduction)

Mutation

A change in a DNA sequence. Happens spontaneously and unavoidably

Alleles

Different versions of the genes for a trait (dominant or recessive)

Grant and Grant

Studied the finch population on an isolated island in the Galapagos.

Measured the beak dimensions of all birds on the island every year for decades.

changes in population can happen very quickly in response to bottleneck

Artificial selection

When reproductive success is determined by human requirements

Biogeography

Fossils distributed in patterns that reflect the continents at one point in time being connected

Transitional Fossils

Show evolutionary progression between groups

Vestigial structures

structures that have lost their primary adaptive purpose

Homologous Structures

Structures present in a common ancestor, which have diverged during evolution. (Divergent evolution)

Analogous Structures

Structures that have evolved multiple times in different lineages to fill similar adaptive needs. (Convergent evolution)

Population

localized group of interbreeding individuals

Gene pool

collection of alleles in the population

Allele frequency

how common that allele is in the population

Evolution

change of allele frequencies in a population

Genetic Drift

• Random, non-selective, changes in allele frequency due to chance. Can lead to loss of genetic diversity.

• Has a larger effect on smaller populations, since each individual is more of the total alleles.

Founder Effect

The descendants of a small, founding population have different allele percentages than the population the founders came from.

Bottleneck Effect

The survivors of a catastrophic decrease in a population may have a different allele frequency than the pre-bottleneck population.

Ex: Earthquake, fire, or flood

Gene Flow

Movement of alleles due to immigration and emigration.

Sexual Selection

Persistence of traits that signify fitness and aid in reproduction.

Directional Selection

• Shifts the overall makeup of the population by favoring variants that are at one extreme of the distribution.

• Darker mice favored living among dark rocks—their darker fur conceals them from predators.

Disruptive Selection

• Favors variants at both ends of the distribution.

• In a patchy habit made up of light and dark rocks, mice of intermediate color are at a disadvantage.

Stabilizing Selection

• Removes extreme variants from the population and preserves intermediate types.

• If the environment consists of rocks of an intermediate color, both light and dark mice will be selected against.

Non-evolving population

• Large size (no genetic drift)

• Random mating (no sexual selection)

• Stable environment (no natural selection)

• No immigration/emigration (no gene flow)

• No mutations.

No real population is in H.W. equilibrium.

Biological species

A group of organisms that are capable of successfully producing fertile, viable offspring.

Gradualism

species are the product of slowly accumulating, small evolutionary changes

Punctuated equilibrium

species undergo long periods of very little change, followed by rapid, large evolutionary changes

Adaptive Radiation

One species evolves into many species that occupy open niches

Reproductive Isolation

Speciation occurs when a population can no longer interbreed with any other population.

Allopatric Reproductive Isolation

• due to physical separation

Sympatric Reproductive Isolation

• Happens while occupying the same area.

Examples: part of population switching to new habitat/food source, or polyploidy plants.

Pre-zygotic

Prevent gametes from combining into a fertilized zygote

Post-zygotic

Prevent the hybrid zygote from becoming an organism capable of reproducing