hardy-weinberg equilibrium if p = frequency of allele a q = frequency of allele a p + q = 1, ( p + q...
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Hardy-Weinberg equilibrium
if p = frequency of allele A q = frequency of allele a
p + q = 1, ( p + q )2 = 1 p2 + 2pq + q2 = 1
if only law of probability affects the frequency w/ which gametes combine to form new individuals
Bisexual population
Large population
Random mating
No mutation
Migration ~ 0
Natural selection does not affect the locus
A population that is in Hardy-Weinberg equilibrium will experience no change in either genotype frequency or allele frequency
If one or more of the conditions is violated, genotype frequency and allele frequency will change
Example If only 6% of the population displays
pale eyes (recessive gene e). What is the frequency of genotype Ee in this population?
q2 = 0.06 ---> q = 0.24
p + q = 1 ---> p = 0.76
Ee = 2pq = 2(0.76)(0.24) = 0.36
Genetic variation Cline – a measurable, gradual change
over a geographical region in the average of some phenotype character
Ecotype – abrupt changes in the phenotype characters within a species, which often reflect abrupt changes in local environment
Geographic isolates – semi-isolated populations prevented by some extrinsic barriers from a free flow of genes
Genetic polymorphism – the existence within a species or population of different forms of individuals
Maintenance of balanced polymorphism
(vs. transitional or directional polymorphism) heterosis diversifying evolution frequency-dependent selection selective forces operating in different
directions within different patches of a fine mosaic in the population
Stabilizing, directional, diversifying or disruptive evolution
Speciation
Allopatric speciation
Sympatric speciation
Isolation mechanism
Pre-zygotic: habitat, temporal, ethological, mechanical
Post-zygotic
hybrid inviability or weakness hybrid sterility F2 breakdown
Reduction in variation
inbreeding, bottlenecks, founder effect, genetic drift
genetic drift - random shifts in allele frequencies
Effect of small populations More demographic variation, inbreeding
depression, genetic drift → higher risk of extinction
Minimum viable population size the threshold # of individuals that will
ensure the persistence of subpopulation in a viable state for a given time interval
Effective population size (Ne) the size of a genetically idealized population
with which an actual population can be equated genetically, Ne = N , if
equal sex ratio
equal probability of mating
constant dispersal rate
progeny per family randomly distributed
unequal sex ratio
Ne = 4 Nm˙Nf / (Nm + Nf )
population fluctuation
1 / Ne = (1 / t )(1/N1 + 1/N2 + … + 1/Nt)
non-random progeny distribution
Nk
Ne = -----------------------------------------(N/N-1)˙Vk/k˙(1+F) + (1-F)
Effect of continental drift
Distribution/radiation of monotremes and marsupials
Extinction and its causes
Natural causes: climatic changes and stochastic event
Human disturbance
habitat alteration over-exploitation exotic species diseases and other factors
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