AP Biology: Unit 7- Evolution

Genetic drift

Genetic drift

species separated by a physical barrier then undergo different selective pressures, therefore evolve separately

bottleneck effect

example of genetic drift that happens when the size of a population is severely reduced due to destruction

founder effect

when a small group of individuals is separated from the rest of the population

sexual selection

compete for access to mates

Allopatric speciation

a population forms a new species while geographically isolated from its parent population

Sympatric speciation

a subset of a population forms a new species without geographic seperation.

Phyletic gradualism

evolution occurs through small gradual changes

Punctuated equilibrium

a sudden event causes rapid evolution

Coevolution

multiple species evolve together because they influence the evolution of each other

Parallel evolution

two distinct species diverge from a common ancestor but develop similar traits independently while living in the same habitat due to similar environmental pressures

Divergent evolution

two species diverge from a common ancestor and develop different traits due to different environmental pressures

Convergent evolution

two species without a common ancestor evolve to develop similar traits due to similar environmental pressures

Adaptive radiation

evolution of a number of divergent species from a common ancestor, each species becoming adapted to occupy a different environment

Analogous structures

same function different structure

Homologous structures

same structure different function

Vestigial structures

remains of structures that served important function in the organism's ancestors, anatomy traces evolutionary history

Heterozygous advantage

the heterozygote is more fit than either homozygote

Balanced polymorphism

occurs when two different versions of a gene are maintained in a population of organisms because individuals who carry both versions are more likely to survive than those who only have two copies of one

5 Hardy Weinberg assumptions

1. no natural selection

2. no mutation

3. no migration

4. large population

5. random mating

Polyploidy

having three or more sets of chromosomes

Prezygotic isolating mechanisms

Sperm does not meet egg

1. geographic isolation

2. ecological isolation

3. temporal isolation

4. behavioral isolation

5. mechanical isolation

6. prevention of gamete fusion

geographic isolation

species occur in different areas separated by physical barriers, eg. river or mountain

ecological isolation

species occur in the same area but occupy different habitats so they typically don’t come in contact with each other

temporal isolation

species reproduce in different seasons/ at different times of day

behavioral isolation

species differ in mating rituals

mechanical isolation

structural differences between species prevent mating

prevention of gamete fusion

gametes don’t work/work well together

Postzygotic isolating mechanisms

hybrid inviability or infertility

hybrid inviability

the embryos do not develop properly and so they do not survive

hybrid infertility

the hybrid adults are sterile

Gamete incompatibility

gamete isolation

Gene flow

the transfer of genetic material from one population to another