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72 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Hardy Weinberg |
Allele genotype frequencies in HW equilibrium do't change from one generation to the next AS LONG AS 5 ASSUMPTION ARE MET |
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5 assumptions of HW equilibrium |
1) no mutation 2) random mating 3) no selection 4) no gene flow 5) infinitely large population size |
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Infinitely large population size |
No populations are infinitely large and therefore we get STOCHASTIC CHANGES |
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Stochastic changes results in |
GENETIC DRIFT |
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NS AND GD |
NS is NOT random. Favours mutations that give adaptive advantage = ADAPTIVE EVOLUTION |
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Genetic Drift |
Random fluctuations in allele frequencies occur as a result of "sampling error" between generations in finite populations |
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Non adaptive elvolution |
replacement of old alleles by new (and trait they confer) |
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Wright 1929 |
"in a freely interbreeding population of limited size, gene frequency shows random variation" |
Genetic Drift |
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Genetic Drift |
Fundamental Evolutionary Force |
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5 fundamental Evolutionary forces |
Selection Gene flow Genetic drift Mutation Recombination |
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Frequency between 1 generation and next |
V= p(1-p)/2n P = allele frequency V = variance |
Equation |
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As populations get bigger... |
Allele frequencies are more similar from one generation to the next |
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NS & GD |
All loci/alleles are subject to GD but NOT necessarily to NS |
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Genetic drift is a |
Null hypothesis to explain adaptive evolutionary change |
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V= p(1-p)/2N |
P = 0.5 IF SAMPLE SIZE = 10 V = 0.5 (1-0.5)/20 V = 0.25/20 V = 0.0125 IF SAMPLE SIZE = 1000 V = 0.5(1-0.5)/2000 V = 0.25/2000 V = 0.000125 HIGHER VARIENCE IN SMALLER POPULATIONS |
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Higher varience in smaller populations |
= GD is MOST important in SMALL populations |
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Loss in heterozygosity |
As allele frequencies drift toward fixation or loss, the frequency of heterozygous decreases |
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HM eq. Equation |
p^2 + 2pq + q^2 =1 |
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2pq = |
Frequency of H p = frequency of allele A1 q = frequency of allele A2 |
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As alleles become fixed or lost in a population |
Heterozygosity falls over time |
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Hg+1 |
Heterozygosity of NEXT generation |
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Hg |
Heterozygosity in CURRENT generation |
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N = |
Number of individuals |
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2N = |
Number of gene copies |
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Value of (1- 1/2N) |
Always between 0.5 (when N =1)
And 1 (when N = infinite) |
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When N=1 |
(1-1/2N) = 0.5 |
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When N = infinate |
(1-1/2N) = 1 |
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H expected frequency in next gen |
Is ALWAYS less than the H frequency of current generation |
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If N is LARGE |
Decrease in H is small |
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If N is small |
Decrease in H is LARGE |
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Ho = |
Heterozygosity of original population |
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Founder effect |
The genetic drift resulting from when a new population is formed by a small number of colonists |
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H in founder effect |
Is not reduced by much in the first generation but will suffer loss of genetic variation Rare alleles are likely to be lost |
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When founder N = 2 |
H is reduced by 25% per generation |
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Founder effect equation |
Ho+1 =Ho (1-1/2N) N = number of founders Ho = homozygosity of original population |
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GD is a |
Predominant force at the genetic, phenotypic, and cultural level |
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GD is unlike NS |
Because it acts on genetic variation in a predictable manner, in relation to population size |
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We compare patterns of DNA variation |
From REAL populations to reconstruct population history |
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Examples of GD - Berthelot's pipit |
GD can explain a 60% variation at neutral genes and 30% variation in morphology |
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Bottlenecks are a better predictor |
Of morphological variation than the environment |
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What can be stronger than selection? |
Drift |
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Cultural change |
Can be used to model cultural change |
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Berthelot's pipet |
Anthus berthelotii |
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Seychelles Warbler |
Acrocephalus sechellensis |
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GD examples - Seychelles Warbler |
Already endangered when discovered Compared DNA between museum and contemporary specimens Used simulations to model GD and reconstruct population history Fount that Seychelles warblers existed in their thousands across region a few hundred years ago. |
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Ne = |
Effective population size |
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Census size |
Number of individuals in a population |
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Factors influencing Ne |
1) variation in number of progeny
2) overlapping generations 3) unequal numbers of males and females 4) fluctuations in population size |
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Ne |
Effective population size |
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Effective population size |
The size of an ideal theoretical population that would lose heterozygosity at the same rate as the actual population |
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Variation in number of progeny |
If some individuals have more offspring than others, Ne will be REDUCED |
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Overlapping generations |
Individuals mate over multiple generations Offspring may mate with parents They carry identical copies of same genes Therefore effective number of genes in the population is REDUCED |
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Unqual numbers of males and females |
Ne = 4(Nm X Nf)/Nm+Nf Nm =number of males Nf = number of females IF EQUAL 50:50 Ne = 4(50 * 50)\50+50 Ne = 10000/100 Ne = 100 IF UNEQUAL 20 males, 80 females Ne = 4(20 * 80)/ 20+80 Ne = 6400/100 Ne = 64 |
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Fluctuations in population size |
Ne is more strongly affected when population is small. Using harmonic mean Nh = K / (1/n + 1/n2 +..........1/nk) If N of breeding adults in 5 successive generations (K) = 100, 150, 25, 150, 125 Ne = 5 / ( 1/100 + 1/150 + 1/25 + 1/150 + 1/125/ Ne = 5 / (0.01+0.0666+0.04+0.0066+0.008) Ne = 70 |
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Human Ne |
Currently tens of thousands. |
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Human census size |
>7, 400, 000, 000 |
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Small Ne leads to |
Drift |
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Drift leads to |
Loss of heterozygosity And any associated benefits (Hz advantage) Loss of genetic diversity (loss of adaptive potential) |
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Hz advantage |
Heterozygosity associated benefits |
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F = |
Coefficient of inbreeding |
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Inbreeding. |
Mating between related individuals Always some degree in small populations |
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Inbreeding coefficient |
Increases more rapidly in small populations than in large population |
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Inbreeding coefficient formula |
ft+1 = 1/2N + (1 - 1/2N) ft |
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F = |
Inbreeding coefficient |
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Inbreeding depression |
Reduces heterozygosity Exposes rare deleterious recessive alleles (as homozygous) Loft of genetic diversity |
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Loss of genetic diversity |
Inability to adapt to new changes E.g. New diseases |
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Reduced heterozygosity |
Reduces associated benefits (heterozygote advantage) |
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Exposure of.. |
Rare deleterious recessive alleles (as homozygotes) |
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Florida panther |
Puma concolor coryi |
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Puma concolor coryi |
1) Tail kink 2) Cryptochidism (>80% males) and deformed sperm 3)Poor fecundity 4)High parasite load and disease susceptibility 5) Atrial septal defects |
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Example of inbreeding depression |
Puma concolor coryi |
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......Effects >80% male Puma |
Cryptorchidism |
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