ap biology notes

evolutioin

The Fossil Record

The history of life on Earth as shown by fossils, showing how organisms have changed over time.

Analogous Structures

Body parts that perform a similar function in different species but do not come from a common ancestor (e.g., bird wing vs. insect wing).

Homologous Structures

Similar body structures in different species that show a common ancestor, even if they have different functions (e.g., human arm and whale flipper).

Vestigial Structures

Structures that have lost most or all of their original function through evolution (e.g., human appendix, whale pelvis).

Founder Effect

A type of genetic drift where a new population is started by a small group of individuals, leading to reduced genetic diversity.

Polymorphic Effect

The presence of two or more distinct traits (forms) within a population due to genetic variation (e.g., different blood types in humans).

Hardy-Weinberg Effect (Equilibrium)

A condition where a population's allele frequencies remain constant unless acted on by outside forces, used to study whether evolution is occurring.

Disruptive Selection

A type of natural selection where individuals with extreme traits are favored over average traits (e.g., both very light and very dark mice survive better than medium-colored ones).

Stabilizing Selection

A type of natural selection where average traits are favored, reducing variation in a population (e.g., medium-sized babies have higher survival).

Directional Selection

A type of natural selection where one extreme trait is favored, shifting the population in that direction (e.g., longer necks in giraffes).

Gene Flow

The movement of genes between populations through migration, which increases genetic variation.

Convergent Evolution

When unrelated species evolve similar traits because they live in similar environments (e.g., dolphins and sharks both have streamlined bodies).

Divergent Evolution

When related species evolve different traits and become more distinct from each other (e.g., Darwin’s finches with different beak shapes).

Genetic Drift

Random changes in allele frequencies in small populations, which can reduce genetic diversity.

Mechanical Isolation

A type of reproductive barrier where species can’t mate because their reproductive parts don’t fit together properly.

Gametic Isolation

A reproductive barrier where sperm and egg from different species can’t fuse or form a zygote.

Habitat Isolation

When species live in the same area but occupy different habitats, so they rarely meet or mate.

Temporal Isolation

When species reproduce at different times of day or different seasons, preventing mating.

Sympatric Speciation

When a new species evolves from a parent species without geographic separation, often due to genetic or behavioral changes.

Fitness

An organism’s ability to survive and reproduce in its environment; the higher the fitness, the more offspring it leaves.

Allopatric Speciation

When a new species forms because a population is split by a physical barrier (e.g., mountains or rivers), leading to reproductive isolation.