Evolution - Test 2
Terms
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Conover and VanVoorhees (1990)
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- populations of silverside fish with environmental sex determination
- placed biased ratio of fish at constant temperatures
- sex ration evolved to 50:50 in 7-8 generations
- Consequences of Genetic Drift
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- Alleles drift to either fixation or loss
- Frequency of heterozygotes declines
- Every population follows it's own unique evolutionary path
- occurs more rapidly in smaller populations
- given enough time
- Consequences of heterozygote Inferiority
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- leads to a loss of genetic diversity within a population
- leads to the maintenance of genetic diversity across populations
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Did inbreeding occur in the sea otter?
- Yes, because there are far fewer SF heterozygotes than expected based on the Hardy-Weinberg equation. Lidicker and McCollum ruled out other explanations.
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Equilibrium depends on...
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- mutation rate of deterious alleles
- strength of selection against alleles
- Eugenics
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a discipline that seeks to improve the human race through selective breeding
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Fisherian sex ration evolution
- sex ratios should evolve to 1:1 through frequency dependant selection for rarer sex
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Formula to figure out probablity a given allele will be fixed through genetic drift
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Population has 2N alleles:
p= 1/2n
If there are x copies of the allele:
p= x/2n (allele frequency)
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Founder Effect
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- a population is usually very small when first established by migrants
- the founders may not have been representative of the allele frequency of the source population
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General Effects of Migration
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- Homogenizing force
- Tends to prevent divergence among populations
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Genetic drift
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Change in allele frequency resulting from:
- sampling error in drawing gameets from the gene pool
- chance variation in the survival and/or reproductive sucess of individualsd
- Gigord, Macnair, Smithson (2001)
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- noticed elderflowers come in two colors in every population
- placed pots of orchids in varying color frequency
- measured amount of pollen removed
- Hardy-Weinberg Principle
- p2+2pq+q2
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Heterozygote Inferiority
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- aka underdominance
- AA and BB have higher fitness than AB
- One of the two alleles tends to die out (same allele does not die out in every population)
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Heterozygote Superiority
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- aka overdominance
- natural selection maintains 2 alleles in the population at a stable equilibrium
- Inbreeding
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- causes genotype frequencies to change across generations
- does not cause allele frequencies to change
- evolution has not occured
- Inbreeding Depression
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- reduced fitness of individuals or populations that results from matings among kin
- inbreeding causes more alleles to be expressed in homozygous state
- deleterious recessive genes get exposed
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Lake Erie Water Snakes
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- Island rocks make plain individuals camoflaged better
- Expect to see allele for plain color increase, but it does nt
- Migration from mainland keeps brining banded alleles into island gene pool
- Lord William Thomson Kelvin
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- assumed Earth was cooling from a molten state
- calculated age of earth based on this assumption
- estimate in conflict with theories by Lyell and Dawin
- Microsatellite
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- short, repeating sequences of noncoding DNA
- tremendous variation in alleles at a single locus
- Migration
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The movement of alleles across population
- movement of actual individuals
- movement of seeds or pollen
- gene flow
- can take allele frequencies away from h-W equilibrium
- Mukai and Burdick (1959)
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- V and L alleles at one loci in Drosophilia
- VV and VL are viable
- LL is lethal
- established populations of 100% heterozygotes
- Heterozygotes had higher fitness than homozygotes <
- Mutation - selection balance
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rate at which they are eliminated is equal to the rate that they appear through mutation (an equilibrium state)
- Pinegal Island
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- colorblindness and sensitivity to light = achromatopsia
- all people descended from 20 individuals in 1775
- One of those individuals was heterozygous for the gene
- RA Fisher
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statistician
continuos variation in a population can be explained by many independent genes for the same trait
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Richard Lenski et al.
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- Bacteria (E. Coli) encapable of conjugating
- Genetic mutation = only source of variation
- survival and cell size increased
- fitness increased in jumps
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Sampling Error
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- random discrepancy between theoretical expectations and actual results
- the error decreases as population size reaches infinity
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Selection Sweeps
- Advantageous mutation sweeps through population and reaches fixation through natural selection
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Self fertilization in snails leads to...
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a loss of heterozygosity across 3 generations
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Sonya Clegg et al.
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analyzed 6 microsat loci and found
- diversity decreased at each island step
- founders for each colony had only a subset of the orginal allele
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TH Morgan
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rediscovered Mendel's principles using fruit flies
theory that genes resided on chromosomes
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The Modern Synthesis
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1930's-1950's
Incorporated a genetic explanation with Darwin theory of national selection
neo-Darwinism
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The question that stumped Darwin
- Why do domestic animals almost always produce males and females in equal amounts?
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The role of mutations in genetics
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- mutation is the source of all new alleles and genes
- weak force of evolution(occurs at a very small rate on their own)
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Theodosius Dobzhansky
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russian, immigrated to US
student TH Morgan
Population genetics and speciation in natural fruit fly populations
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True or False: Nonrandom mating causes evolution
- False!
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Under an infinite amount of time...
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- the beneficialallele frequency will eventually reach 1
- the allele is fixed in the population
- the deterious allele frequency will reach zero
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What happened to the IL Greater Prarie Chicken?
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- Population size went down
- Habitat fragmentation
- creates many small, isolated populations
- these increased role of genetic drift, inbreeding depression and founder effect
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Why eugenics wont work
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- most disease is recessive
- flawed methods of detecting genetic diseases
- disease alleles are often introduced by random mutation
- possible heterozygote superiority