1. Adaptation and Natural Selection
12.4 Warning coloration in a western coral snake (Micrurus euryxanthus)
C:\Figures\Chapter12\high-res\Evolution-Fig jpg

2. The Outcome of Natural Selection Depends Upon:
Relationship between phenotype and fitness.
(2) Relationship between phenotype and genotype.
Determine the relationship between
fitness and genotype.
Outcome determines if there is evolution

3. % survival to reproduction: A = 0.05 B = 0.10
12.2 Growth of 2 genotypes in an asexually reproducing population w/ nonoverlapping generations
% survival to reproduction:
A = 0.05
B = 0.10
Fecundity (eggs produced):
A = 60
B = 40
C:\Figures\Chapter12\high-res\Evolution-Fig jpg
Fitness A = 0.05 x 60 = 3
Fitness B = 0.05 x 60 = 4

4. 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 A
Highest Absolute Fitness
WA = /4 = 0.75
Often by convention, fitness is expressed relative to the genotype with highest absolute fitness.
Thus,
WB = 4/4 = 1.0

5. The fitness of a genotype is the average lifetime
contribution of individuals of that genotype to the
population after one or more generations, measured
at the same stage in the life history.

6. 12.3 Components of natural selection that may affect the fitness of a sexually reproducing organism
C:\Figures\Chapter12\high-res\Evolution-Fig jpg

7. 12.1(1) Modes of selection on a heritable quantitative character
C:\Figures\Chapter12\high-res\Evolution-Fig jpg

8. 12.1(2) Modes of selection on a polymorphism consisting of two alleles at one locus
C:\Figures\Chapter12\high-res\Evolution-Fig jpg

9. Individuals may differ in fitness because of their underlying genotype
Incorporating Selection
Individuals may differ in fitness because
of their underlying genotype
Genotype A1A1 A1A2 A2A2
Frequency p2 2pq q2
Fitness w11 w12 w22
Average fitness of the whole population:
w =
p2w11 + 2pqw12 + q2w22

10. Given variable fitness, frequencies after selection:
Genotype A1A1 A1A2 A2A2
Freq p2 w11 2pq w12 q2 w22 w w w
New allele frequencies after mating:
p2 w11
pq w12
pq w12
q2w22 + + w w
New Frequency of A1
New Frequency of A2

11. 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 s
Fitness is often stated
in relative terms
Selection coefficient
gives the selection differential

12. Persistent Selection Changes Allele Frequencies
(i.e. Evolution by Natural Selection)
Strength of selection is given by the
magnitude of the selection differential

13. Selection Experiments Show Changes in Allele FrequenciesHW
Cavener and
Clegg (1981)
Food spiked
with ethanol

14. Selection can drive genotype frequencies
away from Hardy Weinberg Expectations

15. Predicted change in allele frequencies at CCR5
High frequency (Europe)
High selection/transmisson (Africa)
Predicted
change
in allele
frequencies
at CCR5
High frequency (Europe)
Low selection/transmisson (Europe)
Low frequency (Africa)
High selection/transmisson (Africa)