1. The Evolution of
Populations
Chapter 23

2. THE HARDY WEINBERG
THEOREM:
applies for gene pool of non evolving
population:
very large population size
no migration
no net mutations
random mating
no natural selection

3. THE HARDY WEINBERG
THEOREM
p 2 + 2pq + q2 =1
frequency of frequency
frequency of
RR genotype Rr plus rR of rr
where
p is frequency of one allele (R)
q is frequency of the other allele (r)

4. CAUSES OF
MICROEVOLUTION
microevolution: occurance of small scale changes
in alle frequencies in a population, over a few
generations

5. CAUSES OF
MICROEVOLUTION
Genetic Drift: a change in a small population’s allele
frequencies due to change
~ bottleneck effect: drastic reduction in population
size because of disaster; the survivors makes up new
frequencies of alleles b/c they are unlikely represent
original gene pool
~ founder effect: when few individuals colonize new
area

6. CAUSES OF
MICROEVOLUTION
Natural Selection:
individuals with favorable phenotypes
are more successful in producing
offspring -> favorable genotypes are
increased, thus causing microevolution
Gene flow: migration or
transfer of fametes between
populations
Mutations: changes in
nucleotide sequences

7. NATURAL SELECTION
Relative Fitness: Contribution an organism makes to
the gene pool of the next generation relative to other
members.

8. Directional Selection: Individuals at one extreme are
favored.
Disruptive Selection: Individuals at both extremes are
favored.
Stabilizing Selection: Acts against both extremes and
favors extremediates.

9. Sexual selection may lead to pronounced secondary
differences between the sexes.