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Evolution:
Evidence of Change
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 Agenda
Classroom guidelines
Review for test
Completion of missing work
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etc.)
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 Homework due next class
Evolutionary relationship
Evolution
 Evolution is the process of change in species driven by the
selective pressure of natural agents
 Video on Darwin and evidences of evolution
 https://www.youtube.com/watch?v=XKnqj3YFXU8
 Darwin’s work and original manuscripts (additional info if
you are interested)
 http://darwin-online.org.uk/majorworks.html
 http://www.bbc.co.uk/timelines/zq8gcdm#zxq987h
Evidence for evolution!
 Charles Darwin contributed enormously to our understanding of
the process of evolution
 At the age of 22, Charles Darwin (1809-1882) climbed aboard the
H.M.S. Beagle, to sail the world for 5 years
Carolus Linnaeus (1707-1778)
 Developed modern classification system
 Grouped organisms into taxa
Taxa: Group of one or
more populations that
form a unit
based on similar characteristics (relatedness)
of Organisms
Physical similarities, observable
characteristics
Hinted at the idea of common ancestors
 Developed Binomial Nomenclature
The two name naming system that remains in
use today
Jean Baptiste de Lamarck (1744-1829)
 Brought the idea of evolution to the forefront
 He realized that organisms adapted to their environments
 Lamarck’s theory is based on 3 ideas:
Desire (the will) to change
Use and Disuse
Passing on acquired traits
 Knew nothing of genes or genetics, didn’t understand the how
 He’s known most famously for the giraffe neck stretch
hypothesis
Darwin’s Other Influences contd.
 Alfred Russel Wallace
 Focused on Biogeography of animals.
 Wrote a book ”The geographic distribution of animals”
 Developed the theory “evolution by natural selection”
independently at same time as Darwin (1858--)
 Both Darwin and Wallace presented their work at
Linnaean Society and Wallace insisted that Darwin should
receive the credit
Darwin’s Theory of Natural Selection- Five reasons of Evolution
1.
Overproduction
 Ex. Millions of eggs laid annually by cod fish
 Populations increase geometrically while food resources multiply arithmetically
2.
Struggle for existence (competition)
 Food, water and space
3.
Variation
 Differences in traits among members of same species
 Variation is inherited
4.
Survival of the fittest (natural selection)
 Fitness is not always about strength; it includes any characteristic that increases an
organism’s chances of survival and reproduction
 Fitness arises from a process called adaptation, which is environmental selection of
advantageous characteristics
5.
Origin of new species or the principle of common descent
 New organism come from preexisting organisms; thus, each species has descended
from the offspring of other species over time
Direct evidences of Evolution:
Galapagos finches – Variation in beak
Direct Evidence for Evolution
 Fossils
Preserved remains or traces of an
organism that lived in the past.
Fossils are formed when organisms die
and are buried in sediment. Eventually
the sediment builds up and hardens to
become sedimentary rock.
Direct evidence: Environmental selection –
adaptation - The Peppered Moth
 Spend their time resting on tree
trunks.
 Some are born light coloured;
some are dark
 Can you see them both?
Which one is easier to spot?
 The Industrial revolution in
England deposited large
quantities of soot from
factories, staining the trees.
 Now which is easier to spot?
Lamarck vs. Darwin
 Lamarck
 Environment causes giraffes
to stretch their necks over
their lifetime to better
survive.
 Darwin
 Environment selected that
giraffes born with longer
necks had a greater
chance of survival
Indirect Evidence for Evolution
 Homologous Structures
 Modified body parts with different
functions that developed from the
same ancestral parts
 Embryological Relationships
 Structural similarities between
species during embryonic
development
 i.e. Gill slits in humans
Indirect Evidence for Evolution
 Vestigial Structures
 Structures in the body of
organisms that seem to serve
no useful purpose at all
 May have had a function in
ancestral forms
 Eg. human tailbones, the
appendix
 Muscles that move our ears
 Whale hip bones
Indirect Evidence for Evolution
 Comparative biochemistry and molecular evidence
All organisms have similarities in their biochemistry
 Cytochrome c, Hemoglobin etc.
ATP, Carbon
 The more closely two species are related, the closer the
similarities between their genes
All life has DNA,
Humans share: 98% of our genes with chimpanzees;
65% with chickens; 60% with bananas; 7% with bacteria
Biochemical Relationship- Hemoglobin
Role of DNA in Evolution-We are related to other species
98% of our genes with
chimpanzees;
65% with chickens;
60% with bananas;
7% with bacteria
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Discovery of DNA Structure
 Rosalind Franklin took diffraction x-ray photographs of
DNA crystals
 In the 1950’s, Watson & Crick built the first model of
DNA using Franklin’s x-rays
copyright cmassengale
21
DNA Structure
• Two strands coiled hence called a double helix
• Sides made of a pentose sugar Deoxyribose,
bonded to phosphate (PO4) groups by
phosphodiester bonds
• Center made of nitrogen bases bonded
together by weak hydrogen bonds
copyright cmassengale
22
DNA Double Helix
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone
copyright cmassengale
23
DNA
• Stands for Deoxyribonucleic acid
• Made up of subunits called
nucleotides
• Nucleotide made of:
1. Phosphate group
2. 5-carbon sugar
3. Nitrogenous base
copyright cmassengale
24
DNA Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
copyright cmassengale
C3
C2
Nitrogenous base
(A, G, C, or T)
DNA
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5
O
3
3
P
5
O
O
C
G
1
P
5
3
2
4
4
P
5
P
2
3
1
O
T
A
3
O
3
5
O
copyright cmassengale
5
P
P
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Antiparallel Strands
One strand of
DNA goes from 5’
to 3’ (sugars)
The other strand
is opposite in
direction going 3’
to 5’ (sugars)
copyright cmassengale
27
Nitrogenous Bases
• Double ring PURINES
Adenine (A)
Guanine (G)
A or G
• Single ring PYRIMIDINES
Thymine (T)
Cytosine (C)
T or C
copyright cmassengale
28
Base-Pairings
Purines only pair with
Pyrimidines
Three hydrogen bonds required
to bond Guanine & Cytosine
3 H-bonds
G
copyright cmassengale
C
29
•Two hydrogen bonds are
required to bond Adenine &
Thymine
T
copyright cmassengale
A
30
Discovery of DNA Structure
 Erwin Chargaff showed the amounts of the four bases
on DNA ( A,T,C,G)
 In a body or somatic cell:
A = 30.3%
T = 30.3%
G = 19.5%
C = 19.9%
copyright cmassengale
31
Question:
• If there is 30% Adenine, how
much Cytosine is present?
copyright cmassengale
32
Answer:
• There would be 20% Cytosine
• Adenine (30%) = Thymine (30%)
• Guanine (20%) = Cytosine (20%)
• Therefore, 60% A-T and 40%
C-G
copyright cmassengale
DNA double helix Chemistry
Genes: Unit of Variation
 Darwin’s variation can be best
expressed using the experiments of
Gregor Mendel (1822-1884).
 Mid 19th century, biologists believed
that inheritance was blended
 traits of offspring were the
average of their parents.
 Blended inheritance was discredited
by Gregor Mendel’s experiments,
which showed that inheritance was
particulate. He began our
understanding of genetics.
Mendel’s Experiment
1. Experimented with Pea Plant breeding.
2. Focused on 7 well-defined garden pea traits one at
a time:
•
•
Flower/seed coat color:
purple vs. white flowers
grey vs. white seed coats
Seed color: yellow vs. green
•
•
•
•
•
Seed shape: smooth vs. wrinkled
Pod color: green vs. yellow
Pod shape: inflated vs. pinched
Stem height: tall vs. short
Flower position: axial vs. terminal
Genotype = collection of genes (and alleles) in an organism
Phenotype = observable properties of an organism
Mendel’s Theories
 The genes for different traits are inherited independently of each
other.
 Some exceptions, of course, occur
Incomplete Dominance (blending) for some traits
Codominance (random mixing)
Some genes are sex-linked
Seed shape
Seed color
Pod shape
Mendel’s 7
garden pea
characters.
Pod color
Flower color
Flower location
Plant size
Monohybrid Cross
When he bred a
purebred tall plant with
a purebred short plant,
all off the offspring
were tall
Then, when he bred
two plants of the new
generation together,
he would get 1 short
plant for every 3 tall
plants.
Purebred tall
× Purebred short
F1 generation = all
tall
F1
×
F1
F2 generation = 3 tall : 1
short
Monohybrid Cross - explained
Parental
generation
TT
tt
×
F1 = all Tt
F1generation
This is called
a Punnett’s
Square
Tt
Tt
×
T
t
T
TT
Tt
t
Tt
tt
F2 phenotypic ratio = 3:1; genotypic ratio = 1:2:1
Dihybrid Cross
Pgeneration
Purebred tall ;
Green pods
×
Purebred short;
yellow pods
F1 = all tall; green pods
F1
×
F1
F2 = 9 tall/green : 3 tall/yellow : 3 short/green : 1 short/yellow
The 5 Agents of Evolutionary Change
 Natural Selection
Environmental selection of advantageous traits
 Mutation
Random changes in protein structure (See DNA
presentation)
 Genetic Drift
 Gene Flow
 Non-Random Mating
So, how does Selection work on genes?
 Population
A group of organisms of the same species and
living in the same area
Therefore, sharing the same gene pool
 Evolution works on populations not on individual
organisms
Variation occurs in individuals
Selection shifts the relative frequency and
abundance of alleles in a gene pool
 The Genetic definition of evolution:
Any change in the relative frequency of alleles in
the gene pool of a population.
Types of Selection
 Directional
One extreme form of a trait is favoured
 Stabilizing
Intermediate form of a trait is favoured
 Disruptive
Both extreme forms of a trait are favoured
Genetic Drift
 Random process that increases the specific allele frequency within a
population
Reduces variation within a population, which can result in a lack of
diversity
Promoted allele may not be advantageous
 Occurs most often in smaller populations
 Often due to a disaster or disease event
Surviving individuals have different allele frequencies
than the original population
Reproductive Isolation
Reproductive Isolation
Darwin’s Finches
 Spatial (geographic)
isolation of Finches in the
Galapagos resulted in their
evolution into different
species.
Gene Flow (Migration)
 Gene flow—also called migration—is any movement of genes from one
population to another.
 Ex: pollen being blown to a new destination or people moving to new cities or
countries.
 Can be very important source of genetic variation
Non-random Mating
 Non-random mating
 some organisms are more desirable mates than others.
 organisms with this desirable trait are more likely to mate
and produce offspring with similar characteristics
 Desirable trait may not improve fitness
The Patterns of Evolution
Divergent Evolution
 Reproductive Isolation often results in Divergent evolution
 The process by which one species gives rise to two or more new species, whose traits become more
and more different, but who share a common, structural ancestor
 Produces homologous structures
 Different function, but same origin
Convergent Evolution
 The process by which two or more different species evolve to become structurally similar
 Species must have similar niches
 Ex. shark and dolphin
 Produces analogous structures
 Similar function, but different origin
Parallel Evolution
 The process where two different species follow similar
evolutionary paths
Species must have similar niches
Ex. Timber wolf and Tasmanian wolf
Sleek, hunters, etc…
Co-evolution
 When two or more species influence each other's
evolution.
It is most often invoked to explain coadaptations between species.
Ex: Parasites and Hosts
(antagonistic coevolution)
can lead to evolutionary 'arms races‘
Ex: Insects and Flowering Plants
(mutualistic coevolution)
The Tempo of Evolutionary Change
Gradualism
Theory that evolutionary
change occurs slowly
and gradually
true for many species
in fossil record
 Punctuated Equilibrium
 Term used to describe
a pattern of long
stable periods
interrupted by brief
periods of change.
Living Fossils
 Some organisms have changed very little over the
past million years
 E.g. Ginko biloba (270 MYA)
 Hagfish (300 MYA)
 Red Panda (10 MYA)
 Pelicans (30 MYA)
 Crocodiles (83.5 MYA)
Evolutionary Change
 Rapid Change
 Sometimes something happens to upset
the equilibrium and change happens
rapidly
 Ex: bottleneck, or a small group of organisms
migrates to new environment
 MASS EXTINCTION – many species vanished due
to global climate changes
 When many species die it leaves TONS of
niches unoccupied!!
Historical Mass Extinctions
Suddenly,
Bobby felt
very alone
in the
world