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Evolution of Populations
Is evolution random or non-random? Be
prepared to discuss.
(1) Hand in Chapter 22 Homework and signed
contract (place in folder marked with your
class period)
(2) Write your name and class period on your
lab supply item and place it in the corner of the
classroom in the spot marked with your class
(3) Put away bags and cell-phones – we will
begin with the quiz
Selection In Action
Peppered moths
Darwin’s finches
Antibiotic-resistant bacteria
Lactose tolerance in humans
Modern Evolutionary Synthesis
• Darwin’s theory of evolution by natural
selection lacked an explanation for the basis
of heredity. Genetics helped explain this,
creating a synthesis between the idea of
Darwinian selection and Mendelian genetics.
Evolution of Populations
Population: localized group of individuals
belonging to the same species
Evolution happens on a larger level than the
individual organism – evolution occurs at the
level of populations.
• Population genetics: the study of genetic
variability within populations
• Gene pool: combined aggregate of genes in a
population at any one time
• Species: a group of populations that have the
potential to interbreed and produce fertile
offspring in nature
Hardy-Weinberg principle
• states that allele and genotype frequencies
will remain constant from generation to
generation in the absence of other
evolutionary influences
Hardy-Weinberg Theorem
Very large population size
No migration
No net mutations
Random mating
No natural selection
Mechanics of Hardy-Weinberg
p = allele 1
q = allele 2
p + q = 1 (100% of population)
Note: This is for calculating frequencies of
genotypes when there are only 2 alleles for a
single locus
Punnett Square for Hardy-Weinberg
A (p)
a (q)
A (p)
AA (p2)
Aa (pq)
a (q)
Aa (qp)
aa (q2)
p2 + 2pq + q2 = 1
Bottleneck Effect
Genetic Drift
Founder Effect
Steps of The Scientific Method
Experimental Method
• Only one variable must be tested at a time,
with the result being compared against a
• Independent and dependent variable
Genetic Variation Within Populations
• Polymorphism
• Gene diversity
• Nucleotide diversity
Geographic variation
Maintaining Genetic Variation In
Heterozygote advantage
Frequency-dependent selection
Neutral variation
Modes of Selection
Intrasexual selection
Direct competition among individuals of the same sex
Intersexual selection
Also known as mate choice, when members of one sex are choosy
in selecting mates of opposite sex
Balanced polymorphism
• Ability of natural selection to maintain stable
frequencies of two or more phenotypic forms
Heterozygote advantage
• When individuals that are heterozygous at a
particular locus have a greater survivorship
and reproductive success
Frequency-dependent selection
• Survival and reproduction of any one morph
declines if the phenotypic form becomes too