Transcript Evolution Part 2 - Coosa High School

Evolution, Part II
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Major Elements Of Life
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Carbon C
Hydrogen H
Oxygen O
Nitrogen N
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Chemical Evolution
Simple Molecules
H
H
O
C
O
H
O
H
H
N
H
More Complex Molecules
• Carbohydrates
• Fatty Acids
• Amino Acids
H
H
H
C
H
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H
Carbohydrates
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Fatty Acids
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Amino Acids
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Figure 02.12
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Proteinoid
Microspheres
• Similar to protocells
• Protocells
– Reproduce
– Natural selection
favored those with the
most efficient
replicating systems
• RNA
• DNA
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Cyanobacteria
• Photosynthesis
– Produce oxygen
– Produce
carbohydrates
Carbon Dioxide + Water = Glucose + Oxygen
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Microevolution
• Change in allele frequency of a population
– Populations evolve, individuals do not
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Terms
• Allele
– Member of a paired gene
• Dominant allele
– Allele that is expressed when combined with a recessive allele
• Recessive allele
– Allele that is NOT expressed when combined with a dominant
allele
• Homozygous
– Both alleles the same, AA or aa
• Heterozygous
– Alleles are different, Aa
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Terms
• Codominance
– Both alleles are dominant, AB blood type
• Gene Pool
– All the alleles in a population
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Math Explains Allele
Frequencies
• p +q=1
• p = percent of dominant alleles in a
population
• q = percent of recessive alleles in a
population
• If 70% of alleles in a population are
dominant then 30% must be recessive
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Genotype Frequencies
• Square the equation p + q = 1
• p2 + 2pq + q2 = 1
• Correlation between genotypes and
variables in the equation are:
• p2 = AA
• 2pq = Aa
• q2 = aa
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Hardy-Weinberg Equations
• p +q=1
– Frequency of dominant alleles plus frequency
of recessive alleles is 100% ( or 1)
• p2 + 2pq + q2 = 1
– AA plus 2Aa plus aa add up to 100% (or 1)
• Applies to populations that are not
changing
– They are in equilibrium
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Hardy-Weinberg Example
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Normal pigmentation (not albino) = A
Albinism recessive = a
AA = (p2) = normal
Aa = (2pq) = normal
aa = (q2) = Albinism
1 in 20,000 people have albinism
aa = 1/20,000 = 0.00005
a = 1/141 = 0.00707
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First Equation
• p +q=1
– p is the frequency of the dominant allele, A
– q is the frequency of the recessive allele a
• p + 0.00707 = 1
• p = 1- q = .9929
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Second Equation
• p2 + 2pq + q2 = 1
• p2 = AA
– .9929 x .9929 = .9858
• 2pq = Aa
– 2 x .9929 x 0.00707 = .0140
• q2 = aa
– .00005
• .9858 + .0140 + .00005 = 0.99985 or 1
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Cystic Fibrosis
• Cystic fibrosis affects 1 in 2000 white
Americans
• Cystic fibrosis is recessive = cc
• 1 in 2000 = 1/2000 = .0005
• q2 = .0005
• What is q?
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Value of q
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q is the square root of q2
q2 = .0005
Square root of .0005 = .022
What is p?
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Value of p
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p +q=1
Since q = .022
Then p = .978 (1-.022)
What are the values for p2 and 2pq?
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Values for p2 and 2pq
• P2 = pxp =.978 x .978 = .956
• 2pq = 2 x .978 x . 22 = .043
• 4.3% of population are carriers for cystic
fibrosis
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Problem
• Jack and Jill are expecting a baby. What
is the chance the baby will have cystic
fibrosis?
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Solution
• The chance of Jack being a carrier is .043
• The chance of Jill being a carrier is .043
• The chance of two carriers producing a
child with a recessive trait is .25
• .043 x .043 x .25 = .0046 @ 1/2000
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Practical Application of HardyWeinberg Equations
• If you know the frequency of the recessive
phenotype (aa) you can calculate the
percent of the population that are carriers
(Aa) and that are AA.
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Populations are rarely in HardyWeinberg equilibrium
• Most populations are evolving
• Factors that cause allele frequencies to
change
– Nonrandom mating
– Genetic drift
– Gene flow
– Mutation
– Natural selection
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Nonrandom Mating
• Most people choose their
mates based on
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Physical appearance
Ethnic background
Intelligence
Shared interests
• One-third of marriages
are between people born
less than 10 miles apart
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Religious & Cultural Influences
• Many people will
only marry within
their own religion or
culture
• Consanguineous
marriages increase
risk of birth defects
by 2.5 times
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Hopi Indians
• Albinos stay in village with woman
– Cannot tolerate the sun
• Albinos have more opportunity to mate
with females
• 1/200 Hopi Indians are albino
• 1/8 are carriers
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Genetic Drift
• Change in gene frequency when small a
group of individuals leave or are separated
from a larger population
– Founder Effect
– Bottleneck
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Founder Effect
Original Population
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1% has allele A
Founders
New
Population
10% with A
allele
• 10 people leave to found a new population
• 1 of the founders has allele A
• 10% of new population will have allele A
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Ellis-van Creveld Syndrome
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Dwarfism
Extra fingers
Heart defects
High frequency in Amish
population of Pennsylvania
• A founder of the population
had allele for the syndrome
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Bottleneck
• Population almost dies out
• Survivors genes are at a higher frequency
in the descendants than the original
population
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Cheetah Bottleneck
• 2 major bottlenecks
– 10,000 years ago
– 1800’s
• Present cheetah are
more alike genetically
than inbred lab mice
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Gene Flow
• When genes move from one population to
another
• Genes flow between the two populations below
OKC
Dallas
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Gene Flow
• Can change the
frequency of genes in
a population
• If gene flow stops for
a long period of time
the two populations
may change enough
from each other to
become new species.
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No Gene Flow
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Mutations
• Introduces new alleles into a population
• Most mutations are lethal
– Mutation for no heart would be lethal
• Some mutations are beneficial
– Block infection of HIV
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Beneficial Mutation
• Mutation for albinism
beneficial for bears
who live on the ice
and snow
• Polar bears were
once part of a
population of brown &
black bears
• Now polar bears are a
separate species
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Natural Selection
• Some individuals are more likely to survive and
pass on their genes than others
• Nature selects against gene for black fur in the
arctic
– Black fur does not enable bears in that environment
to survive as well
• Nature selects against gene for white fur in
Oklahoma
– White fur is not as advantageous in Oklahoma
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Tuberculosis
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Number 1 killer in 1900
Antibiotics decreased cases dramatically
1980 very few cases
Bacterium that causes TB is constantly
mutating
• Mutant strains resistant to antibiotics are
naturally selected to survive
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Evolution of Tuberculosis
Cases of TB
1900
1980
2000
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Sickle Cell Anemia Frequency
• Sickle cell anemia is
most common in parts
of Africa with malaria
• Carriers who live in
an environment with
malaria have an
advantage
– Immune to malaria
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Why is the frequency of sickle cell anemia
lower in the USA population of Blacks than
African populations from which they
originated?
• There is no selective
advantage for the s allele
in an environment with no
malaria
• The frequency of the s
allele in the USA Black
population has dropped
significantly in the last 300
years.
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Stabilizing Selection
• Average value
selected for
• Extreme values
selected against
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Directional Selection
• Favors values above
or below average
• Population will shift to
the favored value
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Disruptive Selection
• Extreme traits are
both favored
• Birds with small bills
and large bills are
better feeders
– In a specific
enrironment
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Macroevolution
• Evolution that results in new species
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Allopatric Speciation
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A barrier separates a population into two subpopulations
There is no gene flow between the two populations
Each population changes with time
Changes result in new species.
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Sympatric Speciation
• Different individuals occupy different parts of the
environment
• They breed in the areas they occupy
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Convergent Evolution
• Whales are mammals
• Evolved a fish like body
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Divergent Evolution
Mammal
Reptile
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Bird
Coevolution
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Parallel Evolution
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Gradualism or Punctuated Equilibrium
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