Transcript X. PHYLOGENY, cont

UNIT VIII
EVOLUTION
• Big Campbell
 Ch 22-28, 31
• Baby Campbell
Ch 13-17
• Hillis
Ch 15-18
I. EVOLUTION - WHAT IS IT?
o “Descent with Modification”
Earth’s many species are descendants
of ancestral species that were diff. than
present day species
o
Evolution – change in the genetic
composition of a population over time.
 “Change” – in the genetic
composition (the alleles)
 Population – group of organisms
of one species in a certain habitat
that interbreed to produce fertile
offspring.
November 24, 1859
II. Hardy-Weinberg Principle
• Predicts allele frequency in a
non-evolving population; that is,
a population in equilibrium
o States that allele frequencies
in a population will remain
constant from generation to
generation if five conditions
are met
o Used to identify/study
evolving populations
II. Hardy-Weinberg Principle, cont
• Five Conditions for Hardy-Weinberg Equilibrium:
1) No Mutations – gene pool is modified if mutations alter alleles or if
entire genes are deleted or duplicated
2)
Random Mating – if individuals mate preferentially within a
population (inbreeding), random mixing of gametes does not occur and
gene frequency changes.
3)
No natural Selection – differences in the survival and reproductive
success of individuals carry diff. genotypes and can alter allele
frequencies.
4)
Extremely large population size – the smaller the pop the more
likely allele frequencies will fluctuate by chance from one generation to
the next (genetic drift)
5)
No gene flow (migration) – moving alleles into or out of
populations can alter allele frequencies.
If any of these conditions are not met, evolutionary change will
occur!
II. Hardy-Weinberg Principle, cont
• Hardy-Weinberg Equation
 p = frequency of one allele (A)
 q = frequency of other allele (a)
 p + q = 1 (sum of 2 alleles = 1 or 100%)
• Therefore,
p=1-q
q=1-p
• Genotype Frequency
 AA = p2
 aa = q2
 Aa = 2pq
• To determine distribution of genotype frequencies in a population →
p2 + 2pq + q2 = 1
Ex: PKU in the US
•
•
•
•
•
•
Autosomal Recessive
Occurs 1 in 10,000 births
q2 = .0001
q = .01
p = 1 - .01 = .99
What % of individuals are
carriers for PKU?
• 2pq = 2(.99)(.01) = .0198
or 2%
II. Hardy-Weinberg Principle, cont
Hardy-Weinberg Practice Problems
1. If you know that you have 16% recessive fish (bb), . . .
• q2=
• q=
• Therefore, p =
 To calculate the frequency of each genotype …
• p2 =
• 2pq =
 What is the expected percentage of heterozygous fish?
II. Hardy-Weinberg Principle, cont
• Hardy-Weinberg Practice Problems, cont
2. If in a population of 1,000, 90 show recessive phenotype (aa), use HardyWeinberg to determine frequency of allele combinations.
3. In people light eyes are recessive to dark. In a population of 100 people,
36 have light eyes. What percentage of the population would be …
•
Homozygous recessive?
•
Homozygous dominant?
•
Heterozygous?
II. Hardy-Weinberg Principle, cont
4. The ability to roll the tongue is a dominant trait. … 75% of the students at
Kingwood Park High School have the ability to roll the tongue. Assuming the
student population is 1700,
a) How many students would exhibit each of the possible genotypes?
b) How many students would exhibit each of the possible phenotypes?
III. A HISTORY OF EVOLUTIONARY THEORY
• Aristotle (384-322 BCE)
o Scala Naturae
• Carolus Linnaeus (1707-1778)
o Taxonomy
III. A HISTORY OF EVOLUTIONARY THEORY, cont
III. A HISTORY OF EVOLUTIONARY THEORY, cont
• Charles Darwin (1809-1882)
III. A HISTORY OF EVOLUTIONARY THEORY, cont
• Darwin, cont
o Observed many examples of
adaptations
Inherited characteristics
that enhance organisms’
survival and reproduction
o Based on principles of
natural selection
Populations of organisms
can change over the
generations if individuals
having certain heritable
traits leave more offspring
than others
Differential reproductive
success
III. A HISTORY OF EVOLUTIONARY THEORY, cont
• Darwin’s Conclusions
 Based on his own observations and
the work of other scientists, Darwin
realized …
o Members of a population often
vary greatly in their traits.
o Traits are inherited from parents to
offspring.
o All species are capable of
producing more offspring that their
environment can support,
therefore …
III. A HISTORY OF EVOLUTIONARY THEORY, cont
 Darwin concluded …
o Individuals whose inherited traits
give them a higher probability of
surviving and reproducing in a
given environment tend to leave
more offspring than other
individuals.
o This unequal ability of individuals
to survive and reproduce will lead
to the accumulation of favorable
traits in the population over
generations.
 Descent with Modification
III. A HISTORY OF EVOLUTIONARY THEORY, cont
Human Directed Evolution?
• Artificial Selection
– Selective Breeding
– Transgenic Organisms
III. A HISTORY OF EVOLUTIONARY THEORY, cont
• Post-Darwin
Neo-Darwinism/Modern Synthesis Theory
Epigenetics
IV. EVIDENCE FOR EVOLUTION
• Direct Observation
o Antibiotic/Drug Resistance
IV. EVIDENCE FOR EVOLUTION, cont
• Fossil Record
o Succession of forms over time
o Transitional Links
o Vertebrate descent
IV. EVIDENCE FOR EVOLUTION, cont
• Homology
o Homologous structures
o Vestigial organs
Snakes
Cetaceans
Flightless birds
IV. EVIDENCE FOR EVOLUTION, cont
o Convergent Evolution
 Independent evolution of similar features in different lineages
 Analogous structures
IV. EVIDENCE FOR EVOLUTION, cont
• Biogeography
o Geographical distribution of
species
o Continental Drift
Pangaea
o Endemic species
o Islands are inhabited by
organisms most closely
resembling nearest land mass
IV. EVIDENCE FOR EVOLUTION, cont
• Comparative
Embryology
o Pharyngeal
Pouches
 Gill slits
o Tail
IV. EVIDENCE FOR EVOLUTION, cont
• Molecular Biology
o Similarities in DNA,
proteins, genes, and gene
products
o Common genetic code
V. MICROEVOLUTION
• A change in the gene
pool of a population
over a succession of
generations
• Five main causes:
 Mutation
 Non-Random
Mating
 Natural Selection
 Genetic Drift
 Gene Flow
V. MICROEVOLUTION, cont
• Genetic Drift
o
o
o
o
Changes in the gene pool due to chance.
More often seen in small population sizes.
Usually reduces genetic variability.
There are two situations that can drastically reduce population size:
Bottleneck Effect
Founder Effect
V. MICROEVOLUTION, cont
• Bottleneck Effect
 Type of genetic drift resulting
from a reduction in population
(natural disaster)
 Surviving population is no longer
genetically representative of the
original population
• Founder Effect
 Due to colonization by a
limited number of individuals
from a parent population
 Gene pool is different than
source population
V. MICROEVOLUTION, cont
• Gene Flow
 Genetic exchange due to the
migration of fertile individuals
or gametes between
populations – tends to reduce
differences between
populations
V. MICROEVOLUTION, cont
• Mutations
 A change in an
organism’s DNA
(gametes; many
generations); original
source of genetic
variation (raw material
for natural selection)
V. MICROEVOLUTION, cont
• Nonrandom Mating
 Inbreeding – reduces fitness
by putting an individual at a
greater risk of harmful
recessive traits.
 Assortative mating –
individuals with similar
genotypes/phenotypes mate
more frequently than expected
V. MICROEVOLUTION, cont
• Natural Selection
 Blend of Chance and Sorting
chance in the creation of new
genetic variations; sorting b/c
natural selection favors some
alleles over others
 Relative fitness – contribution an
individual makes to the gene pool
of the next generation
 Only form of microevolution that
adapts a population to its
environment
VI. VARIATION IN POPULATIONS
• Genetic Variation is the
“substrate” for evolution
• Maintained through …
 Polymorphism
 Coexistence of 2 or more
distinct forms of individuals
(morphs) within the same
population
 Geographical Variation
 Differences in genetic
structure between
populations (cline)
VI. VARIATION, cont
 Mutation and Recombination
 Diploidy
 2nd set of chromosomes hides
variation in the heterozygote
 Balanced Polymorphism
 Heterozygote Advantage
 Frequency-Dependent Selection
o Survival & reproduction of
any 1 morph declines if it
becomes too common
o Parasite/host
VII. A CLOSER LOOK AT NATURAL SELECTION
• Natural Selection
Not a random process → Dynamic process
Increases frequency of alleles that provide reproductive
advantage
Fitness
VII. CLOSER LOOK AT NATURAL SELECTION, cont
 Natural selection is the only evolutionary mechanism for adaptive
evolution
VII. CLOSER LOOK AT NATURAL SELECTION, cont
• Three ways in which
natural selection alters
variation
Directional
Disruptive
Stabilizing
VII. CLOSER LOOK AT NATURAL SELECTION, cont
• Sexual Selection
 Can result in sexual
dimorphism - secondary
sex characteristic
distinction
 Intrasexual Selection
- within the same sex;
individuals of one sex
compete directly for mates
of the opposite sex
 Intersexual Selection
- individuals of one sex are
choosy in selecting their mate
(male showiness)
VIII. MACROEVOLUTION
• Macroevolution
 Refers to the formation of new taxonomic
groups
 Due to an accumulation of microevolutionary
changes
 AKA Speciation
•
“Species”
 Morphological Species Concept - charac.
species by body shape & other features; can be
applied to sexual & asexual organisms
 Ecological Species Concept – views a species
in terms of its niche; which is the sum of how
members interact w/living & non-living parts of
environ; can accommodate sex & asexual
 Phylogenetic Species Concept – smallest
group of individuals that share a common
ancestor; forming 1 branch on tree of life
VIII. MACROEVOLUTION, cont
• Biological Species Concept
 Described by Ernst Mayr in
1942
 A population or group of
populations whose members
have the potential to interbreed
and produce viable, fertile
offspring; in other words, similar
organisms that can make
babies that can make babies 
 Can be difficult to apply to
certain organisms . . .
VIII. MACROEVOLUTION, cont
• Reproductive
Isolation
o Prevent closely
related species
from
interbreeding
when their ranges
overlap.
o Divided into 2
types
Prezygotic
Postzygotic
VIII. MACROEVOLUTION, cont
Prezygotic Reproductive Barriers
VIII. MACROEVOLUTION, cont
Postzygotic Reproductive
Barriers
VIII. MACROEVOLUTION, cont
• Speciation
o Fossil record shows evidence of bursts of many new
species, followed by periods of little chance
Known as punctuated equilibrium
o Other species appear to change more gradually
Gradualism fits model of evolution proposed by Darwin
VIII. MACROEVOLUTION, cont
• Modes of Speciation
 Based on how gene flow is
interrupted
 Allopatric
 Populations segregated by a
geographical barrier; can result
in adaptive radiation (island
species)
 Sympatric
 Reproductively isolated
subpopulation in the midst of
its parent population (change
in genome); polyploidy in
plants; cichlid fishes
IX. HISTORY OF LIFE ON EARTH
IX. HISTORY OF LIFE ON EARTH, cont
• Formation of Organic Molecules
o Oparin/Haldane Hypothesis
 Primitive Earth’s atmosphere was a
reducing environment
 No O2
 Early oceans were an organic “soup”
 Lightning & UV radiation provided
energy for complex organic
molecule formation
o Miller/Urey Experiment
 Tested Oparin/Haldane hypothesis
 Simulated atmosphere composed of
water, hydrogen, methane, ammonia
 All 20 amino acids, nitrogen bases,
ATP formed
 Hypothesis was supported
IX. HISTORY OF LIFE ON EARTH, cont
IX. HISTORY OF LIFE ON EARTH, cont
IX. HISTORY OF LIFE ON EARTH, cont
• Mass Extinctions
IX. HISTORY OF LIFE ON EARTH, cont
• Adaptive Radiation
o Periods of
evolutionary change,
increased speciation
o Often due to
increased ecological
niches in
communities
o Also seen in
organisms with major
evolutionary
innovations


X. PHYLOGENY
Phylogeny – study of how living things share common evolutionary history (relationships
among organisms)
- Constructed based on physical structures, behaviors, and biochemical attributes
- Commonly used to depict evolutionary history of species, populations, and genes.
X. PHYLOGENY
• Taxonomy
 Carrolus Linnaeus
 Binomial
nomenclature – 2 part
naming system; genus
and species
 Taxon (taxa) – which is
any group of species
that we designate with a
name. EX: humans,
primates, mammals
 KPCOFGS
 Domain is broadest;
organisms not as
closely related
 Species is most specific
X. PHYLOGENY, cont
• Phylogenetics
 Tracing of evolutionary
relationships
 Illustrated with diagrams
known as phylogenetic
trees
 May portray all life, or a
major evolutionary
group such as insects or
mammals.
 Common ancestor is
called the “root”
X. PHYLOGENY
• Tree Terminology
 Root – common ancestor of all
organisms in the tree.
 Node – or split when a single lineage
divides into two; giving rise to new lineages
 Clade
 Any taxon that consists of all
evolutionary descendants of a common
ancestor
 Clades are sub-categorized as
Monophyletic – Includes ancestral group and all descendants
Paraphyletic – Includes ancestral group and some, but not all descendants
Polyphyletic – Includes taxa with multiple ancestors
 Sister Clades – any 2 clades that are each other’s closest relatives
 Sister Species – two species that are each other’s closest relatives
Monophyletic – “single tribe”
Paraphyletic
ancestral group and some, but not all
descendants
“beside the tribe”
Paraphyletic
Polyphyletic
Includes taxa with multiple ancestors
EX: Kingdom Protista
Polytomy
• Unresolved pattern of
divergence
• More than 2
descendant groups
emerge
• Evolutionary
relationships are not
clear
X. PHYLOGENY, cont
• Evolutionary
history of an
organism
X. PHYLOGENY, cont
• Important to distinguish
between homologies
and analogies
 Homologies are
likenesses attributed to
common ancestry
 Analogies are
likenesses attributed to
similar ecological roles
and natural selection
• May also be done at a
molecular level
 Known as molecular
systematics
X. PHYLOGENY, cont
• Tree Construction, cont
 Ancestral Trait – trait from which organisms evolve; found in common ancestor
 Derived Traits – new traits that evolved after ancestral trait
 Synapomorphies – shared among a group of organisms; viewed as evidence
for common ancestry of group. EX: vertebral column of vertebrates
 May see evolutionary reversals – a character may revert from a derived state
back to an ancestral state. EX: finstetrapodsfins in whales/dolphins
 Ingroup
 Groups of organisms being considered, phylogenetically organized
 Outgroup
 Group chosen as point of reference for tree
 Closely related but diverged before the ingroups
X. PHYLOGENY, cont
• Tree Construction, cont
 Parsimony
 Also known as Occam’s Razor
 Principle that if multiple trees are possible, the correct one is most often the
simplest one; one that takes the fewest assumptions
X. PHYLOGENY, cont
X. PHYLOGENY, cont
X. PHYLOGENY, cont