Lecture 8-Speciation

Lecture 8-Speciation - Population genetics •...

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1 Population genetics • Hardy-Weinberg equilibrium explains why  dominant alleles don’t replace recessive  alleles in a population
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2 Population genetics • Hardy-Weinberg equilibrium is RARE in  nature!
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3 Population genetics • If  allele frequencies deviate from Hardy- Weinberg equilibrium. ....    . ..then evolutionary processes are occurring!
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4 Population genetics This is because in nature there is – Selection. ... – Migration (gene flow). ... – Small populations (inbreeding). ... – Non-random reproduction. ... – Mutation – Random chance events (genetic drift)
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5 Genetic Drift • Genetic Drift = a random fluctuation in  allele frequencies due to sampling error
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6 Genetic Drift (sampling error) http://evolution.berkeley.edu/evosite/evo101/IIID1Samplingerror.shtml
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7 Genetic Drift
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8 Genetic Drift • Genetic Drift = a random fluctuation in  allele frequencies due to sampling error • Larger populations are less likely to be  affected
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9 Genetic Drift • Genetic Drift = a random fluctuation in  allele frequencies due to sampling error • Larger populations are less likely to be  affected • Small populations more likely to lose alleles  due to random fluctuations
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10 Genetic Drift • Leads to fixation of some alleles • Leads to loss of other alleles • Leads to an overall decline in genetic  variation over time
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11 Genetic Drift cont’d. • Affects small populations more dramatically  and more quickly • Can contribute to speciation by causing an  isolated population to diverge
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12
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13
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14 Founder Effect • Consider a colonization event where some  individuals leave the population and form a  new population
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15 Founder Effect • Consider a colonization event where some  individuals leave the population and form a  new population • Allele frequencies in a new population are  likely to be different than those in the  original population
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16 Founder Effect
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17 Founder Effect: Examples • Amish – High incidence of Ellis van Creveld syndrome  (dwarfism + polydactyly; hole in the heart; nail  and teeth deformity) – One couple carried in 1744, passed to children – Intermarriage spread trait
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18 Founder Effect: Examples • Afrikaners in South Africa – Originated from a few Dutch settlers – High incidence of Huntington’s disease – Founders carried Huntington’s disease allele at  higher fq. than general population; over time it  spread through S. African population
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19 Population Bottleneck http://evolution.berkeley.edu/evosite/evo101/IIID3Bottlenecks.shtml
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20 • Cheetahs • Florida panthers • Northern elephant seals – Heavily hunted in 1800’s – Population crashed to ~20 individuals – Now population ~30,000 – Reduced genetic variation compared to Southern  elephant seals (a less hunted population) Population Bottleneck Examples
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This note was uploaded on 08/30/2008 for the course BIOS 230 taught by Professor Gibbons during the Spring '08 term at Ill. Chicago.

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Lecture 8-Speciation - Population genetics •...

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