12.4 Warning coloration in a western coral snake (Micrurus euryxanthus) Adaptation and Natural...
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Transcript of 12.4 Warning coloration in a western coral snake (Micrurus euryxanthus) Adaptation and Natural...
![Page 1: 12.4 Warning coloration in a western coral snake (Micrurus euryxanthus) Adaptation and Natural Selection.](https://reader036.fdocuments.in/reader036/viewer/2022062422/56649f1e5503460f94c3655b/html5/thumbnails/1.jpg)
12.4 Warning coloration in a western coral snake (Micrurus euryxanthus)
Adaptation and Natural Selection
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The Outcome of Natural Selection Depends Upon:
(1) Relationship between phenotype and fitness.
(2) Relationship between phenotype and genotype.
Determine the relationship between fitness and genotype.
Outcome determines if there is evolution
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12.2 Growth of 2 genotypes in an asexually reproducing population w/ nonoverlapping generations
% survival to reproduction:
A = 0.05B = 0.10
Fecundity (eggs produced):
A = 60B = 40
Fitness A = 0.05 x 60 = 3Fitness A = 0.05 x 60 = 4
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R = Per Capita Growth Rate = Represents Absolute Fitness
The rate of genetic change in a populations depends upon relative fitness:
Relative Fitness of A = Absolute fitness AHighest Absolute Fitness
WA = 3/4 = 0.75
Often by convention, fitness is expressed relative to the genotype with highest absolute fitness.
Thus,WB = 4/4 = 1.0
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The fitness of a genotype is the average lifetimecontribution of individuals of that genotype to thepopulation after one or more generations, measuredat the same stage in the life history.
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12.3 Components of natural selection that may affect the fitness of a sexually reproducing organism
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12.1(1) Modes of selection on a heritable quantitative character
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12.1(2) Modes of selection on a polymorphism consisting of two alleles at one locus
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Genotype A1A1 A1A2 A2A2
Frequency p2 2pq q2
Fitness w11 w12 w22
Individuals may differ in fitness because of their underlying genotype
Incorporating Selection
Average fitness of the whole population:
p2w11 + 2pqw12 + q2w22w =
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Given variable fitness, frequencies after selection:
Genotype A1A1 A1A2 A2A2
Freq p2 w11 2pq w12 q2 w22
w w w
New Frequency of A1
New allele frequencies after mating:
New Frequency of A2
p2 w11
w
pq w12 pq w12
w
q2w22+ +
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Fitness: Probability that one’s genes will be represented in future generations.
Hard to measure. Often, fitness is indirectly measured:(e.g. survival probability given a particular genotype)
WAA WAa Waa
1 1 1 + s
Selection coefficientFitness is often stated in relative terms gives the selection differential
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Persistent Selection Changes Allele Frequencies(i.e. Evolution by Natural Selection)
Strength of selection is given by themagnitude of the selection differential
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Selection Experiments Show Changes in Allele Frequencies
Cavener and Clegg (1981)
Food spiked with ethanol
HW
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Selection can drive genotype frequenciesaway from Hardy Weinberg Expectations
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Predicted change in allele
frequencies at CCR5
High frequency (Europe)High selection/transmisson (Africa)
High frequency (Europe)Low selection/transmisson (Europe)
Low frequency (Africa)High selection/transmisson (Africa)