Transcript II. Hardy-Weinberg Principle, 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”
o
 “Change”
 Population
November 24, 1859
II. Hardy-Weinberg Principle
• Means used to determine if a population
is evolving
• Predicts allele frequency in a nonevolving 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
II. Hardy-Weinberg Principle, cont
• Five Conditions for Hardy-Weinberg Equilibrium:
1)
2)
3)
4)
5)
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 =
• Therefore,
p=
q=
• Genotype Frequency
 AA =
 aa =
 Aa =
• To determine distribution of genotype frequencies in a population →
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 High School have the ability to roll the tongue. Assuming the
student population is 2526,
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
• Artificial Selection
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:





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
 Assortative mating
V. MICROEVOLUTION, cont
• Natural Selection


 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
 Intersexual Selection
VIII. MACROEVOLUTION
• Macroevolution
 Refers to the formation of new
taxonomic groups
 Due to an accumulation of
microevolutionary changes
 AKA Speciation
•
“Species”
 Morphological Species Concept
 Ecological Species Concept
 Phylogenetic Species Concept
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


IX. HISTORY OF LIFE ON EARTH, cont
X. PHYLOGENY
• Taxonomy
 Linnaeus
 Binomial nomenclature
 Taxon (taxa)
X. PHYLOGENY, cont
• Evolutionary
history of an
organism
X. PHYLOGENY, cont
• Phylogenetics
 Tracing of
evolutionary
relationships
 Illustrated with
diagrams known as
phylogenetic trees
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
• Cladistics
 Use of common ancestry as primary criterion for classification
 Species are put into groups known as clades
 Includes ancestral species + descendents
 Clades are sub-categorized as
Monophyletic – Includes ancestral group and all
descendents
Paraphyletic – Includes ancestral group and some, but
not all descendents
Polyphyletic – Includes taxa with multiple ancestors
 Parsimony – Also known as Occam’s Razor
X. PHYLOGENY, cont
X. PHYLOGENY, cont