Chapter 11
“The Mechanisms of
Evolution”
 Section 11.1 “Darwin Meets
DNA”
• Objective: Identify mutations
and gene shuffling as the
primary sources of inheritable
variation.
Review

Inheritable traits: traits that are
passed from one generation to the
next.
 Genes: carry info that determines
traits
 Genotype: genetic make-up
 Phenotype: Physical, behavioral, and
biochemical characteristic
Inheritable Traits
 Since
genes are the carriers of
traits ---> then they are also the
source of inheritable variation.
 Two types:
• Mutations
• Gene Shuffling
Mutation
 Change
in a DNA sequence that
effects genetic information.
 Rate vary: Humans vs. Bacteria.
 Reasons: mistakes during
replication, radiation, chemicals
 Can effect fitness (ability to
survive)
Gene Shuffling
 The
possible combination
of genes passed on from
parents to offspring.
 Results of sexual
reproduction.
 EX: deck of cards; same
cards different hands.
Inheritable Variation
 Visible:
• Color of flower petals.
• Size of humans.
 Not Visible:
• Protein synthesis
• Enzyme action
Controlled Traits
 Some
are controlled by single
genes (widow’s peak) some by
several genes (height).
 Single gene: 2 or 3 possible
phenotypes.
 Polygenic gene: Many
phenotypes.
Natural Selection
 Natural
Selection acts on an
organisms phenotypes not
genotype.
 Phenotype = the interaction
between genotype &
environment.
 N.S. determines which alleles are
passed on to the next generation.
Species
 A group
of similar individuals
that can breed with one
another and produce fertile
offspring = population.
 Separation of populations or
species so they cannot
interbreed is called
reproductive Isolation.
Assignment
 Outline 11.2
Review 11.1

Two types of Inheritable Traits
• Mutation
• Gene Shuffling
 Natural Selection
• Acts on Phenotype not Genotype.
 Species, Population, & Reproductive
Isolation.
 Single-gene Traits vs. Polygenic
Traits.
“Evolution as Genetic
Change” 11.2
 Objective:
• Discuss the concept of Gene
Pools.
• Define Evolution in terms of
Genetics.
• Describe Speciation.
Gene Pool
 “Pool”
refers to a grouping
of resources.
 Entire collection of
individual genomes in a
population of organisms.
Evolution
 Species
do not evolve, but
populations do.
 Evolution is any change in
the frequencies of alleles in
a gene pool of a species.
Traits
 Single-Gene Traits
• Harmful
• Helpful
 Polygenic Traits
• Remember polygenic traits may
produce many phenotypes.
• Directional, Stabilizing, &
Disruptive.
Natural Selection on
Polygenic Traits
 Graphs
of variation display a
bell-shaped curve or normal
distribution.
 Fitness can vary from one end
to another.
 Nat. Sel. can affect
distribution of curve.
Figure 16–6 Graph of Directional
Selection
Section 16-2
Key
Directional Selection
Low mortality,
high fitness
Food becomes scarce.
High mortality,
low fitness
Figure 16–8 Graph of Disruptive
Selection
Section 16-2
Disruptive Selection
Low mortality,
high fitness
High mortality,
low fitness
Population splits
into two subgroups
specializing in
different seeds.
Beak Size
Number of Birds
in Population
Key
Number of Birds
in Population
Largest and smallest seeds become more common.
Beak Size
“Other Mechanisms for
Evolutionary Change”
 Genetic Drift is a random
change in allele frequency.
 Less common
 More likely to occur in
smaller population.
Genetic Drift cont...
 Small groups of organisms
colonize a new habitat.
 May carry different alleles
than original population.
 Genetically different species
are produced.
Speciation (page 251)
 The formation of a new
species.
 In order to occur, species
must evolve enough genetic
changes (by N.Sel.)so
inbreeding cannot occur.
The Pace of Evolution
 Evolution
occurs as a result of
Natural Selection & Genetic Drift.
 Gradualism = is the idea that
evolution occurs slowly.
 Punctuated Equilibrium = long
periods of stability followed by
interrupted periods of rapid
change.