Unit 7. Evolution

Evolution

an accumulation of hereditary changes in a population over time

Microevolution

small genetic changes over time

Macroevolution

significant genetic & physical changes over time that lead to speciation

Fitness

ability to survive & reproduce successfully in a given environment

Differential survival and reproduction

only some can survive and reproduce due to a selective pressure

Adaptation

traits/behaviors that help with survival and reproduction

Heritable

parents pass on traits to offspring

Acquired trait

traits that change throughout a lifetime

Adaptive radiation

rapid diversification from an ancestor to fill ecological niches

Directional selection

one version of a trait demonstrates higher fitness than its opposite (positive selection)

Disruptive selection

both extreme versions of a phenotype have higher fitness

Stabilizing selection

an intermediate phenotype has higher fitness

Artificial selection

humans breed organisms for certain traits

• humans affect the variation in other species

Allele frequency

the amount of an allele in a population

Mutation

introduce new alleles to populations

• changes the allele frequency

Genetic drift

random chance events can change allele frequencies in a population

• lucky enough to survive→reproduce

• grater effect on smaller populations

Founder effect

a small portion of the original population migrates & starts a new population

• the allele frequencies are based on founding population

Bottleneck effect

the initial population numbers significantly decline

• new population reflects survivors

Gene flow

migration changes allele frequency

• immigration

• emigration

• decrease differences between populations

• increase diversity

Immigration

enter a new population

Emigration

leave a population

Sexual selection

occurs when mates are selected

• based on: appearance, mating behaviors

Female choice

females within a population select a mate based on criteria

Male competition

males compete for the opportunity to mate with females within the population

Hardy-Weinberg equilibrium

states conditions where a population would not evolve

• in the absence of evolutionary forces, allele frequencies remain constant

• hypothetical, mathematical model

Allele frequency

p + q = 1

• p: frequency of dominant allele

• q: frequency of recessive allele

Genotype frequency

p² + 2pq + q² = 1

p²: frequency of homozygous dominant genotype

2pq: frequency of heterozygous genotype

p²: frequency of homozygous recessive genotype

Fossil

preserved remains or imprints of once-living organisms

• can be used in different ways to understand evolution

• age of rock = age of fossil

The fossil record

help create the story of evolutionary change

Radiometric dating

helps determine the age of rock layers

Half-life

the amount of time that it takes for 50% of a substance to decay

Carbon-14 dating

measures carbon isotope composition (must have been living)

• good for things < 60,000 years old

Uranium-lead dating

measures uranium & its decay products (must have been nonliving)

• good for things 1mya - 4.5bya

Index fossil

characteristic of a particular time period in Earth’s history

Transition fossil

demonstrate evolutionary intermediate forms (between two species)

Biogeography

the study of the distribution of species over geological time

Homologous structure

• show common ancestry

• similar composition; different species

• show descent from a common ancestor

Analogous structure

• show independent evolution

• similar functions but different composition

• do not represent common ancestry

• show similar structures evolve independently in similar environments

Vestigial structure

• show ancestral relationships

• serve no necessary function to a species

• may have been important in ancestral species

Comparative embryology

compares structures that may not be present in adults

• homologous structures in embryos suggest a common evolutionary ancestor