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65 Cards in this Set
- Front
- Back
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Is mutation a mechanism of evolution? Can it cause evolutionary change? |
Yes, No. It causes heritable variation which is essential to evolution. BUT mutation alone does not significantly change allele frequencies. |
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Why can't mutation alone cause allele frequency changes? |
Mutation is random and rare. The likelihood that that many individuals produce gametes with the same mutation in any one generation is low. |
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What is one of the highest mutation rates per locus? |
10^-4 is among the highest ever reported |
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What is population genetics? |
Theory that allows us to track the fate of alleles and genotypes across generations. It can produce quantitative measures of evolutionary change. |
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What are the mechanisms of evolution? |
Natural selection, Mutation, Migration, and Genetic drift. |
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Why are population genetics important? |
Can give us insight into the natural world, insight into human diseases and conditions, and it gives us insight into how our actions affect populations. |
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What do we need to know to figure out frequency of alleles? |
Number of individuals showing those alleles, the genotypes, and the average fitness. |
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What do you do if you want to know if the frequency of an allele is decreasing or increasing? |
Calculate frequency of alleles in each generation, and test if allele is changing. Compare data to a null model (what is expected if there is no evolution). |
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What does the Hardy Weinberg equilibrium do? |
Allows calculation of expected allele and genotype frequencies if evolution has not occured. |
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What is assumed for the Hardy Weinberg model to work? |
No selection, no mutation, no migration, no genetic drift, random mating. No evolutionary change.
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What are the possible genotypes for the two alleles A1 and A2? |
A1A1, A1A2, A2A2. |
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In a gene pool with two alleles, what are the initial frequencies of each allele? |
A1=p A2=q p+q=1 |
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What is the Hardy Weinberg general case? |
P^2 + 2PQ + Q^2 = 1 P^2 + P(1-p) = P (1-q)q + q^2 = q |
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Why in the Hardy Weinberg equilibrium do allele frequencies remain the same? |
No alleles are removed, no alleles are added, and no random loss of alleles. |
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Why do we need to measure allele frequency changes and not just genotype frequency changes? |
The genotypes will change over time because the number of homozygotes, heterozygotes will change, but the same alleles will always be there. Genotypes change but alleles stay the same. |
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What is mutation rate? |
Rate at which one allele is converted to another allele (per generation). u |
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How do we measure the change in alleles due to mutation? |
If mutation causes A to become a then, P*=p-up Q*=q+up |
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Is the effect of mutation significant? |
It can change alleles slightly in one generation, but it is not significant. |
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What is needed to make mutation an evolutionary force? |
Selection and time |
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What happens if mutation is beneficial? |
The mutation is selected for, and the allele increases in frequency over generations. |
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What happens if the mutation is deleterious? |
The mutation is not selected for, the allele is lost, and may be gone within one generation. |
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Explain the experiment with E.coli. |
They took a single cell of E.coli, the strain had no recombination, and put it in a nutrient limited medium. This way, mutation was only source of genetic variation, and it was a stable environment. They then let it multiply for 10 000 generations. By the end, the relative fitness increased by 0.2. Proving that mutation is significant over time with selection. |
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What would happen if the E.coli experiment had no selection? |
The mutations would have caused the population to stop and die. |
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What increases the chances of beneficial mutations arising? |
Time and large populations. |
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How do find what the frequency of genotypes is after selection? |
Find how many individuals are in each genotype, then apply the percent survival to that number to find new number of individuals. Then find new frequency. So if survival is 90%, then multiply by 0.9. |
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How do you approach finding if allele frequencies change? |
Follow the life cycle. Allele frequencies (gametes), genotype frequencies (zygotes), # of individuals (population), fitness (who survives), find genotypes frequency (among parents), calculate allele frequency (gametes). |
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Consistent selection leads to what? |
Consistent directional change. |
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Stronger selection leads to? |
More rapid change/ |
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Explain the Drosophila melanogaster experiement. |
It was a planned experiment to test for selection. The gene Adhf breaks down ethanol 2x faster than Adhs. The flies were given food with ethanol in it, and then over 50 generations, the frequency of Adhf was much greater. They also did this experiment with normal food, and the frequency of Adhf stayed the same. The ethanol experiment is against HW. |
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Why is the Drosophila a natural experiment> |
The experiment does not change X or Y, the alleles are not changed. It only chnages the environment, and then the frequency changes were observed. |
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What is the mutation which causes the inability to feel pain? |
The mutation is in teh SCN9A gene, and it is in three places. It codes for missense mutations which causes the amino acids to not form and then the sodium channels for pain do not form. |
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What are the two broad categories of selection? |
Patterns that maintain genetic diversity, and patterns that reduce it. |
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What is negative frequency dependent selection? |
Fitness increases as an allele becomes rare, and fitness decreases as an allele becomes common. Fitness of genotype depends on frequency in population. Selection favours first allele, then the other. |
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What is heterozygote superiority? |
When the heterozygote genotype has the highest fitness, and has the highest frequency. |
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What happens when on allele is favoured? |
Often leads to fixation of favoured allele and loss of other allele. The rate of change depends on initial frequency of each allele, and dominance. |
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What does it mean for an allele to be fixed or lost? |
Its frequency is = 1 when fixed, and 0 when lost. |
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What is heterozygote inferiority> |
When the heterozyote genotype has the lowest fitness. Often leads to fixation of one allele and loss of the other allele. Which allele is lost depends on inital frequencies and relative fitness of homozygotes. |
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Explain the scale-eating cichlids. |
They eat scales taken from sides of victims, and 20% of attacks are successful. There are right handed fish (Rr, RR) which attack left side of victims, and left handed fish which attack right side (rr). These fish are in a negative frequency dependent selection. |
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What is a human example of negative frequency dependent selection? |
Left handed ness because being left handed caused a change in combat. |
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Which patterns of selection maintain genetic variation? |
Negative frequency dependent selection and heterozygote superiority, and mutation selection balance, and migration selection balance.
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Which pattern of selection reduces genetic varitaion? |
One allele favoured. |
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What pattern of selection does heterozygote inferiority do? |
Reduces variation within population, but maintains varitation among populations. |
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What happens when there is a recessive lethal allele? |
It takes a very long time for the recessive allele to die out because the heterozygotes still have the recessive allele, and this will last for a long time. The recessive allele is hidden from selection this way. |
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What causes a rapid decrease in frequency? |
When there are high frequencies of recessive lethal alleles and many copies are found in homozygotes. |
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Why do some lethal alleles remain at equilibrium despite selection? |
The rate of loss (selection) = rate of cretaion (mutation). There is a mutation selection balance. |
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What is the equation for when mutation and selection are at balance? |
q= squareroot (u/s) where q is the frequency fo the deleterious allele, and s is the selection coefficient.
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What is an example of heterozygote superiority> |
Sickle cell anemia |
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WHat is MHC? |
Major histocompatibility complex. It is central to vertebrate immune system. Encodes proteins that recognize foreign antigens and triggers immune response. MHC loci are highly polymorphic and show high heterozygosity because hetero is more resistant to a wider range of parasites. |
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What is outbreeding depression? |
Two populations have diverged sufficiently that hybrids have low fitness. This may occur at specific loci ro across entire genome. |
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What does Prdm9 gene do? |
It is a polymorphic gene found in humans and mice and effect progress of meisosis by determining meiotic hotspots. In male mice, heterozygotes are sterile. There is heterozygote inferiority, and this created a new subspecies of mice from partial reproductive isolation.
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What is gene flow? |
Transfer of alleles from one gene pool to another population caused by movement of individuals. |
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What is the equation for effect of migration? |
Pi*=(1-m)Pi + mPc Pi is the initial frequency on island, Pc is frequency on continent. M= #migrants/(#migratrants + # islanders) |
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What does migration depend on? |
difference between Pi and Pc, and # of migrants relative to island population size. |
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Why does migration lead to violation of HW? |
Island allele frequency will change over time, and the iland genotype frequency is unpredictable until there is a round of mating. |
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Explain the water snakes exmaple. |
There is one gene with 2 alleles, dominant is banded, and recessive in unbanded. Banded is higher fitness on mainland, and lower fitness on islands. On the islands then, there are still banded snakes because there are continusoulsy snaked migrating and reintroducing the banded genotype. |
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Explain the stickleback fishy |
There is a larger body which is better for streams, and a smaller body for lakes. They did a study with 16 pairs of lake and streams, and the more migration there was, the lesser of a difference there was between the sizes of the two types of fish. |
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What are some things about migration? |
It decreases adaptation to local conditions. Homogenizes allele frequencies (makes allele frequencies mroe similar among populations than they would be otherwise.) and can result in stasis despite selection if there is selection-migration balance. |
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Why are deleterious alleles maintained in populations? |
heterozygote advantage, deleterious recessive alleles, mutation, migration. |
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What is genetic drift? |
Change in the frequencies of alleles in a populaiton resulting from chance variation in the lifetime reproductive success of individuals. |
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How is genetic drift different from natural selection> |
It is based on chance, not phenotype. |
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In what does genetic drift have the strongest effect? |
Small populations. |
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What is the result of genetic drift> |
Random fixation alleles, loss of heterozygosity, and decrease in geentic variation within populaitons. |
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WHat is the founder effect? |
Change in allele frequencies when a new popualtion is estbalished by a small number of individuals with different allele freuqencies from original populaiton. (so some animals move from a continent to an island). |
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What is a bottleneck? |
When a large-scale random disaster happens which kills most of the popultion and the survivors build up the new population. |
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Give me a summary of genetic drift. |
Random, does NOT lead to adaptation, leads to random fixation of alleles, most powerful in small popualtions, most powerful in absense of selection. |
