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What is Fisher's Theorem of Natural Selection?
The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time.
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What is the equation for Fisher's Theorem?
- dr / dt = sigma squared
- where r = intrinsic rate of growth
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What is absolute fitness denoted by?
W
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What is relative fitness denoted by?
w
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How is relative fitness calculated?
- divide all absolute fitnesses by the highest one
- one value always equals 1.0, and the rest are less than that
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How is absolute fitness calculated?
observed number with given genotype in one generation divided by observed number of that genotype in previous generation
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Fitness is a prediction based on observations; not _______.
survival
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The fittest _____________ survive, and the survivor is __________.
does not necessarily survive; not necessarily the fittest
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What is the marginal fitness?
- wA or wa
- the sum of relative fitnesses of genotypes containing the allele in question weighted for their respective frequencies
- wA = pwAA + qwAa
- wa = pwAa + qwaa
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Always calculate p as ___________ not as p^2. Why?
- (nAA + nAa/2)/N
- only use p^2 if it's in HW equilibria
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Selection can act on _________________, ___________, ____________, and __________________.
the level of formation of mating pairs (sexual selection), fertility (ability to produce functional gametes), fecundity (reproductive success of mating pairs), and viability (survival to adulthood)
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What is viability?
survival to reproductive age
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What is fecundity?
actual reproductive output in numbers
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What is fertility?
ability to reproduce, make gametes
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What is the equation for fitness? What do the variables mean?
- w = 1 - s
- w is the fitness coefficient
- s is the selection coefficient
- w is the proportion that survive to reproduce
- s is the proportion that die
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What does it mean if all three relative fitnesses = 1?
The population is in HW equilibria
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What are some characteristics of selection against a completely dominant condition (if p is high)?
- AA and Aa are equally selected against
- aa has so few numbers that even though they produce more offspring, it takes a long time for them to outnumber AA and Aa
- fixation of the recessive allele takes place in a realistic timeframe
- the lower w is relative to 1.0, the more rapid the fixation of aa
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What are some characteristics of selection against a completely recessive condition (if p is low)?
- p rises rapidly
- even under strong selection, recessive allele persists for MANY generations because it hides in the heterozygotes
- of all genotypes containing a, q/(1-p) is proportion of homozygotes, 2p/(1+p) is proportion of heterozygotes
- the lower w is realtive to 1.0, the more rapid the change in p
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How do you calculate mean fitness?
p^2wAA + 2pqwAa + q^2waa
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What does it mean if mean fitness (w line hat) adds up to less than 1?
selection is present
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