Evolutionary Genetics 02
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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.
What is the equation for Fisher's Theorem?
- dr / dt = sigma squared
- where r = intrinsic rate of growth
What is absolute fitness denoted by?
What is relative fitness denoted by?
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
How is absolute fitness calculated?
observed number with given genotype in one generation divided by observed number of that genotype in previous generation
Fitness is a prediction based on observations; not _______.
The fittest _____________ survive, and the survivor is __________.
does not necessarily survive; not necessarily the fittest
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
Always calculate p as ___________ not as p^2. Why?
- (nAA + nAa/2)/N
- only use p^2 if it's in HW equilibria
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)
What is viability?
survival to reproductive age
What is fecundity?
actual reproductive output in numbers
What is fertility?
ability to reproduce, make gametes
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
What does it mean if all three relative fitnesses = 1?
The population is in HW equilibria
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
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
How do you calculate mean fitness?
p^2wAA + 2pqwAa + q^2waa
What does it mean if mean fitness (w line hat) adds up to less than 1?
selection is present
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