Transcript Chapter 17 – Origin of Life

Genetic Engineering
Chapter 16 – Population Genetics
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Population Genetics
 The study of microevolution
Microevolution
 Change within species
 Occurs over hundreds of
generations
Macroevolution
 Occurs over long periods of time
 Origin of new species
Gene Pool
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All genes of a local
population of
organisms
Refers to the
“frequency” of certain
types of alleles
Example – Plants
Gene pools refer to
ONE population, not
an entire species
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They interbreed
Polymorphism
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No two organisms are
exactly alike
Caused by differences in
genes (alleles)
If two or more alleles of
a gene are present in a
gene pool – population is
POLYMORPHIC
The butterfly Heliconius erato has multiple
mimetic forms, controlled by many loci
scattered at random among the
chromosomes. Three of these forms are
displayed here.
The Hardy-Weinberg Model
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Idealized mathematical model of gene pools
Many assumptions!
Model predicts a relationship between allele frequencies and the
expected genotype frequencies
p = dominant allele frequency
q = recessive allele frequency
p+q=1
P2 = homozygous dominant
Q2 = homozygous recessive
2pq = frequency of heterozygous dominant plants
What’s the point?
 Use the allele frequencies to predict genotype
frequencies
Hardy-Weinberg Practice Problem
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Problem: 1 in 1700 US Caucasian newborns have cystic
fibrous. C for normal is dominant over c for cystic fibrous.
1. When counting the phenotypes in a population why is cc the
most significant?
2. What percent of the above population have cystic fibrous?
Now calculate the expectant frequencies of all the following:
 Allele frequency (p and q)
 Frequency – homozygous dominant individuals?
 Frequency – heterozygous dominant individuals?
An example of Hardy-Weinberg
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If 9% of an African population is born with
a severe form of sickle-cell anemia (ss),
what percentage of the population will be
more resistant to malaria because they
are heterozygous(Ss) for the sickle-cell
gene?
The Solution
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9% =.09 = ss = q2
()s = q = Square root of .09 = .3
p = 1 - .3 = .7
2pq = 2 (.7 x .3) = .42 = 42% of the
population are heterozyotes (carriers)
The Assumptions
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Highly idealized
Assumes allele frequencies are the same
over time
Chapter 17 – Origin of Life
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Theory
How did the universe form?
Big Bang Theory
Is the universe still expanding?
Redshift
Quiz – Earth Science Revisited
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How old is the Universe?
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How old is Earth?
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Big Bang occurred ~ 15 bya
About 4.6 byo
How did the Earth Form?
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Nebula Hypothesis
Earth’s Early Atmosphere
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From volcanic gasses
N2, CO2, H2O, H2, CO
No oxygen! 1st organisms were anaerobic
How did oxygen accumulate in our
atmosphere?
Photosynthetic organisms (3-3.5 bya)
How did life begin on Earth?
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Which one is most widely accepted/easier to
investigate?
Life originated on some planet/star
Life originated by unknown means on Earth
Life evolved from nonliving substances
through interaction with the environment
Chemical Evolution
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Complex organic “soup” formed
in oceans by:
Energy sources
 Radioactivity
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Lightening
Cosmic radiation
Heat from volcanoes
ORGANIC CMPDS formed
Heterotroph Hypothesis
(Oparin and Haldane)
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Need supply of organic molecules
Process had to assemble molecules into
polymers such as?
Nucleic acids and proteins
Other processes had to organize the
polymers into a system that could replicate
itself
Urey-Miller Experiment
Urey-Miller Experiment
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Urey-Miller Experiment
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1950’s
Recreated conditions like those 4.6 bya
Water vapor circulated, cooled condensed
Simulated gases, rain, lightening
Small black tar; water was red
Liquid contained organic molecules
Urey-Miller Experiment
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Changed gases – CO2, water, nitrogen,
hydrogen
Made simple amino acids
Recent experiments – 13 of 20 amino acids
produced; ribose sugars
Deep sea vents – organic molecule
Eukaryotic Evolution
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Lynn Margulis
Eukaryotes – originated as free-living prokaryotes
Endosymbiont Hypothesis
ENDOSYMBIONTS
Symbiosis between large anaerobic prokaryotes and
smaller aerobic or photosynthetic prokaryotes
Why? Photosynthesis and aerobic respiration in
small cells produced sugars benefited host cells
Evidence – mitochondria have own DNA and
ribosomes