Population Genetics, Evolution, & Genetic Inheritance

complete dominance

only one dominant allele

codominance

more than one dominant allele (blood types)

incomplete dominance

no dominant alleles; heterozygotes have intermediate phenotypes = blend of all (pink flowers)

expressivity

the varying phenotypic outcomes of a genotype (passion)

genetic leakage (flow)

flow of genes between species via hybrid offspring; contributes to evolution but is not required

genetic drift

when the composition of the gene pool changes as a result of chanceevents that affect allele frequencies.

molecular clock

the degree of difference in the genome between 2 species is related to the amount of time since the two species broke from a common ancestor

bottlenecks

genetic drift due to some external event; chance external events

founder effect

bottlenecks that suddenly isolate a small population; inbreeding is an extreme genetic drift that causes a change in ALLELE FREQUENCIES not fitness

genetic mutation

without mutation, evolution cannot occur

fitness

a quantitative measure of natural selection → differing survival and reproduction based on favorable traits → evolution

what things must an evolutionary system have

variation, reproduction, differential reproduction due to selective pressure

group selection

natural selection applied to the group level

inclusive fitness

individuals can benefit from helping relatives because relatives can share some of their DNA, which may be passed on to the next generations; not needed for evolution; altruism & empathy

modern synthesis model; neo-darwinism

mutation and recombination are mechanisms of variation/differential reproduction

punctuated equilibrium

considers evolution to be a very slow process with intermittent rapid burst of evolutionary activity

Hardy-Weinberg Equilibrium

model stable gene pools; not real-world populations; mathematical relationship b/w allele and phenotype frequencies

Criteria of HW Equilibrium

no mutation, random mating must occur, no gene flow, large population size, no natural selection

In HW Equilibrium, P+Q =

100% for allele frequency calculations

In HW equilibrium, P²+2pq+q²=1

P2 = dominant

2pq = hetero

q = recessive

Stabilizing selection

favors intermediate phenotypes NOT extremes

Directional selection

favors an extreme phenotype in one direction

Disruptive selecton

favors extreme phenotypes over intermediate phenotypes (Galapagos pigeons)

reproductive isolation

reproductively isolated from each other by pre- or post-zygotic mechanisms

prezygotic barriers

prevent a zygote from forming

postzygotic barriers

prevent a formed zygote from being viable or fertile (ex, Mules are hybrids and infertile)

divergent evolution

when species diverge from a common ancestor to become more genetically and phenotypically different

convergent evolution

when two different species independently evolve the same or similar trait and become more phenotypcally similar

coevolution

evolution of two species in response to each other; common in symbiotic relationships

types of symbiotic relationships

mutualism, commensalism, parasitism

mutuaism

both organisms benefit

commensalism

only one benefits, other is not really affected either way

parasitism

one benefits at the expense of the other (host)

parallel evolution

when two closely related species share a common ancestor and evolve similar traits but independently of each other

law of segregation

an organism has 2 alleles for each gene that separate at anaphase I; gametes have 1 allele for a given trait

law of independent assortment

inheritance of one allele does not influence the probability of inheriting a given allele for a different trait (except for linked genes)

genetic linkage

debunks law of independent assortment because cross testing will not follow the rules in results

gain of function

tend to be dominant mutations

loss of function

tend to be a recessive mutations

mendelian dihybrid cross-ratio

9:3:3:1, 1 = recessive traits, 9 = dominant traits

what experiments helped dictate that DNA is genetic material

griffith, avery-macleod-mccarty, hershey-chase

avery-macleod-mccarty experiment

degradation of DNA (not proteins) led to a cessation of bacterial transformation

hershey-chase experiement

only radiolabeled DNA could be found in bacteriophage-infected bacteria

recombination frequency

likelihood of two alleles being separated during crossing over in meiosis