MECHANISMS OF
EVOLUTION
MICROEVOLUTION VS.
MACROEVOLUTION
 Macroevolution
examines the change
of organisms over long periods of time.

It examines the formation of new species
 Microevolution
examines the little
changes that occur over shorter
periods of time

Includes: Mutations, Gene pools, sexual
selection
MICROEVOLUTION – SICKLE CELL
DISEASE

Sickle cell anemia is a genetic
condition whereby red blood cells
deform into crescent shaped blood
cells.



Symptoms: weakness, pain, damage
to organs, and death
In Canada: Sickle cell disease
affects only 1 in 3800 individuals.
In Africa: Sickle cell disease affects
1 in 25 individuals
WHY?
SICKLE CELL BLOOD CELLS
SICKLE CELL GENETICS
 The
allele for the sickle
cell allele is recessive

Therefore an individual
must have the homozygous
recessive alleles in order to
have sickle cell anemia.

Heterozygous individuals do
not contain the sickle cell
disease.

They are carriers
THE HETEROZYGOUS ADVANTAGE

Individuals with at least one
sickle allele are resistant to
malaria



Malaria: Insect infection causing:
fever, joint pain, vomiting, vision
problem, and death
Malaria is common in countries
such as Africa
Heterozygous individuals are
resistant to malaria and do not
have sickle cell anemia.

Selective advantage
SICKLE CELL ANEMIA


As with the sickle cell anemia example, the
environment places a selective pressure on which
alleles are more likely to be expressed in a population.
Since the sickle cell allele helps prevent the
contraction of malaria, it will be expressed more in a
population.
GENE POOLS AND VARIATION


The total amount of unique alleles in a population is
referred to as its gene pool.
The more alleles that exist within a population, the
greater the variability.
GENE POOLS AND VARIATION STATISTICAL
DEMONSTRATION
SOURCES OF VARIATION

1.
Variation results from two main
sources:
Mutations
Is a change in the sequence of DNA due to
errors in DNA replication
o
o
o
2.
Caused by radiation
Can be in the form of a substitution, insertion,
deletion, frameshift.
Sexual Reproduction
During sexual reproduction the alleles from
both parents undergoes DNA recombination.
o
o
I.e. Alleles will exchange part of their DNA
o
This will increase the possibility for variability
DEMONSTRATION – SEXUAL REPRODUCTION
AND MUTATION DIVERSITY
CHANGES TO GENE POOLS – HARDY
WEINBERG EQUILIBRIUM

Godfrey Hardy and Wilhelm Weinberg examined
gene pools and created a model to predict gene pool
frequencies.

The Hardy Weinberg equilibrium (equation)
explains how under standard conditions a population
will maintain a constant gene pool frequency.
Frequency is expressed as a
decimal or percentage
THE HARDY WEINBERG FIVE CONDITIONS

1.
2.
3.
4.
5.

In order for the Hardy Weinberg equilibrium to hold
true five conditions must be in place.
Mating must be random
There is a large population
There is no movement in or out of the population
There are no mutations
There is no natural selection
If these conditions are not met then genetic
equilibrium may be changed leading to
microevolution (altered gene pool frequencies)
HARDY WEINBERG EQUILIBRIUM –
SAMPLE PROBLEM PART 1


Human albinism is a condition whereby
individuals lack the skin and hair pigment
melanin. Albinism occurs in 1 out of 20,000
individuals with the homozygous recessive
genotype.
Using the H-W equation, which percentage of the
population would you anticipate to have the
homozygous dominant genotype and the
heterozygous?
HARDY WEINBERG EQUILIBRIUM –
SAMPLE PROBLEM PART 2

Assume that you have done research and
recorded that 25% of the population is
heterozygous for albinism. What are you able to
conclude from these results?
MECHANISMS OF
MICROEVOLUTION
5
1.
2.
3.
4.
5.
factors can cause microevolution
Natural selection
Sexual selection
Artificial selection
Genetic drift
Gene flow
1- NATURAL SELECTION

Refers to how the environment increases the
frequency of alleles which provide a
reproductive advantage to individuals.
 Leads

to the evolution of adaptations
The environment will place a selective
pressure to certain phenotypes.

Individuals with the adapted phenotypes to the
environment are more fit to reproduce.
DIFFERENT TYPES OF SELECTIVE
PRESSURES
o Stabilizing
selection
o Directional
selection
o Disruptive
selection
STABILIZING SELECTION


Occurs when individuals
near the centre of the
phenotype range have a
higher fitness than
individual’s at either end.
E.g. Medium brown mice
are at an advantage over
dark or light coloured
brown mice
E.G. 2 STABILIZING SELECTION



Skinny mice do not have
enough energy to go out and
search for food
Fat mice are too slow to
avoid predators
Medium sized mice are at a
selective advantage as they
have enough energy but are
not too overweight.
DIRECTIONAL SELECTION


Occurs when individuals at
one end of the phenotypic
range have higher fitness
than individuals at the
opposite end of the
phenotypic range.
E.g. Darker coloured
brown mice are at an
advantage over lighter
coloured mice.
E.G. 2 DIRECTIONAL SELECTION:
PESTICIDE RESISTANCE
DISRUPTIVE SELECTION



Occurs when individuals in
the upper and lower end
ranges of the phenotypic
spectrum have higher
fitness than individuals in
the middle.
E.g. Dark and light coloured
mice are at advantage over
medium coloured mice.
Can lead to two new species
E.G. 2 DISRUPTIVE SELECTION: FINCHES


The brown and white African
Swallowtail mimics and
undesirable prey.
The brown and orange female
African Swallowtail also mimics
and undesirable prey.


Both are undesirable to prey
The brown and white
swallowtail does not mimic
undesirable prey

Is at a selective disadvantage
2- SEXUAL SELECTION


Mating is not random
Males often have secondary sexual
characteristics
I.e. Characteristics that are not reproductive but
rather are used to attract females.
 E.g. Peacock elaborate tails, bright plumage on male
birds, mating dances/rituals.


Sexual selection is a form of natural selection
in which certain individuals with certain traits
are more likely to reproduce.
CASE STUDY: WILLOWBIRDS SEXUAL
SELECTION



An experiment was
conducted to examine the
influence of male tail length
and mating.
Male willowbird tails were
either shortened, uncut, cut
and re-glued, or lengthened
Results showed that longer
tails unaltered increased
reproductive success

A secondary reproductive
characteristic
VIDEO - SEXUAL SELECTION:
MATING RITUALS – PARADISE BIRDS
VIDEO - SEXUAL SELECTION: MATING
RITUALS – CUDDLE FISH
3- ARTIFICIAL SELECTION

The intentional selection of favourable traits by
breeding specific organisms together.
E.g. 1 Milk Breeding in cows


Cows that produce more milk are bred with other cows that
produce more milk
Eventually high milk producing cows are the prominent
gene pool frequency.
E.G. 2 THE AMERICAN QUARTER HORSE



The American Quarter Horse is
known for its speed.
This species of horse was created
by breeding quick horses
together that had strong
muscular limbs.
Side effect: Many descendents
developed hyperkalemic periodic
paralysis
VIDEO - ARTIFICIAL SELECTION
MUSCULAR COWS
ARTIFICIAL BREEDING – NAZI HUMAN
EUGENICS
NAZI’S – EUGENICS AND SELECTIVE
BREEDING
4- GENETIC DRIFT



Is a random process
Genetic drift is a change to the gene pool of a
population due to chance
E.g. Wildflower population
GENETIC DRIFT
All
populations are subject to
genetic drift
Smaller
populations however are
more influenced by genetic drift.
GENETIC DRIFT – THE BOTTLENECK
EFFECT



Occurs when a disaster
occurs (e.g. earthquake,
floods, droughts, fires)
which drastically reduces
the population.
By chance, some alleles
will survive while others
may not.
The end result is a
reduction in genetic
variability and different
gene pool frequencies.
E.G. BOTTLENECK CHEETAH


Cheetahs were nearly hunted to extinction
Severely reduced the genetic variability of the
population

Reduces the adaptability of the species
GENETIC DRIFT – THE FOUNDER EFFECT


Occurs when a few individuals colonize an
isolated island, lake, or some new habitat.
The new individuals will contribute to the genetic
variability of that island.
5- GENE FLOW


Gene flow involves the exchange of genes with
another population usually due to migration.
Commonly occurs in plant populations.