Natural Selection

Darwin and Wallace

independently came to the conclusion of natural selection

homologous structures

common ancestry; ex - forelimbs in whales, humans, and bats

analogous structures

convergent evolution; ex - flying in butterflies, birds, and flying squirrels

Hardy - Weinberg’s Five Conditions

(1) random mating

(2) large population

(3) no migration

(4) no natural selection

(5) no mutations

alleltic frequence (p is…q is..)

p is dominant, q is recessive

genotypic frequency

AA = p²

Aa = qp or pq

aa = q²

phenotypic frequency (how to see expression of dominant trait)

dominant trait showing is either AA or Aa, but if the recessive traits shows, it is only aa

how to find heterozygous frequency

2pq or 2qp

Directional Selection

favors traits that are at one extreme of a range of traits

Disruptive Selection

occurs when environmental conditions favor individuals on both extremes

Stabilizing Frequency

eliminates individuals that have extreme or unusual traits

sexual selection

the idea that a certain fitness/characteristic about a mate that makes the candidate more desirable

intrasexual selection

fighting among the same sex for mates (ex: in lion packs, there is only one male with multiple female partners)

intersexual selection

mate choice (ex: birds of paradise female birds choose from the male birds)

sexual dimorphism

males and females have different appearances (ex: male lions have manes and female lions do not; male peacocks are beautiful and colorful while female peacocks are brown)

founder effect

small group of a population leaves original location to establish new, isolated population. leads to reduced genetic diversity and higher frequency rate of rare traits or diseases

bottleneck effect

population size is drastically reduced leading to loss of genetic diversity and increases the risk of inbreeding and expression of recessive traits

prezygotic barriers

(1) Habitat/Geographical Isolation

(2) Mechanical Isolation

(3) Gametic Isolation

(4) Temporal Isolation

(5) Behavorial Isolatiion

Postzygotic Barriers

(1) Reduced Hybrid Viability

(2) Reduced Hybrid Fertility

(3) Hybrid Breakdown

Habitat/Geographical Isolation

species live in different locations

Behavioral Isolation

different mating rituals

Temporal Isolation

different mating seasons; not active at the same time (up at night vs up at day)

Mechanical Isolation

physically cannot reproduce

Gametic Isolation

sperm and egg do not recognize each other as compatbile

reduced hybrid viability

miscarriage; development incomplete

reduced hybrid fertility

offspring is sterile (ex: mule)

hybrid breakdown

offspring have reduced viability or fertility (common in plants) over generations

hybrid zone

region where different species meet and mate

reinforcement

hybrids stop being produced

fusion

separate species fuse into one

stability

hybrids continue to be produced

allopatric speciation

occurs when there is a geographical barrier or habitat isolation that prevents the two species from interacting with one another (barriers)

sympatric speciation

usually due to sexual selection or mate choice. can also occur due to lack of or too much competition of a food source. occurs when there is a new species within the parents population (no barriers)

Miller - Urey Experiment (Abiotic Origin Theory)

began with inorganic substances (specifically ones that were present during the formation of the Earth’s atmosphere) and were able to form organic substances in a closed system

Extra - terrestrial origins

initial life form came to Earth from meteorites and asteroids (space rocks)

RNA World Hypothesis

RNA is the original genetic material and DNA came along later

Endosymbiont Theory

mitochondria and chloroplasts were free-living bacteria engulfed by a eukaryote and formed a symbiotic relationship