bio 210b lect. 2

genetic variation

difference in genes/DNA sequences

ways to increase genetic variation

1. mutation: random changes in DNA

2. decrease generation time: Increased chances for mutations

3. gene duplication: extra genes to mutate

4. sexual reproduction: crossing over, independent assortment, random fertilization

Hardy-Weinburg Equilibrium equation

p²+2pq+q² = 1 = no evolution

5 conditions for nonevolving population

1. no gene flow

2. random mating

3. no natural selection

4. no mutation

5. large population(infinite)

genetic drift

chance fluctuations of genes from one generation to the next

2 types of genetic drift

1. Founder Effect

2. Bottleneck Effect

Founder Effect

migration/geographic results in a new population whose gene does not represent original

Bottleneck Effect

random natural disaster can remove a portion of population —> resulting population’s gene pool does not represent original

gene flow

movement of genes from one population to another

how may gene flow increase and/or decrease genetic variation

genetic pollution:unwanted gene introduced reduces fitness

3 modes of natural selection

1. directional

2. disruptive

3. stablizing

directional natural selection

one phenotype favored over the other

disruptive natural selection

two different phenotypic extremes are favored voer anything in between

stablizing natural selection

middle phenotype favored

biological definition of species

a group of individuals that can interbreed in nature & produce fertile/viable offspring

prezygotic barriers

1. habitat isolation: different habitats —> different to mate

2. temporal isolation: different mating seasons

3. behavioral isolation: species-specific courtship ritual

4. mechanical isolation: physically unable to interbreed

5. gametic isolation: gametes require a recognition molecule for fertilization

postzygotic barriers

1. reduced hybrid viability: hybrid offspring is frail

2. reduced hybrid fertility: hybrid offspring is sterile

3. hybrid breakdown: hybrid offspring can reproduce, but its offsprings either frail/sterile

speciation

process by which one species split into two or more species

2 ways speciation can occur

1. allopatric

2. sympatric

allopatric speciation

gene flow interrupted/reduced when population is divided into geographically isolated subpopulation

sympatric speciation

speciation takes place in geographically overlapping population

what’s different about natural selection compared to genetic drift & gene flow

natural selection favors adaptive traits while genetic drift and gene flow complete dependent on random chance