The document discusses key concepts related to evolution including natural selection, descent with modification, mutations, adaptations, genetic variation, genetic drift, microevolution, macroevolution, speciation, and coevolution. It explains how small gradual changes over extremely long periods of time through various evolutionary mechanisms like natural selection can result in major changes within populations and the formation of new species through the process of descent with modification.
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Origins of Life 2 - Mechanisms
1. Origins of Life
Mechanisms of Evolution
- Natural Selection -
2. What is Evolution?
Simple:
"change over time"
Less Simple:
"descent with modification"
• many, many, MANY small changes
over LOOOOOOOOONG periods of
time that result in the formation of
many DIFFERENT types of organisms
3. Descent with
Modification
Given enough time, many
small changes could add
up to big changes within
populations of organisms
Mechanisms of change:
• mutation
• migration
• natural selection
• genetic drift
Requires a very, very,
very, very, VERY long
time to happen
4. Gene Frequency
Evolution occurs when there is
a change in gene frequency
within a population over time.
• Gene frequency:
the percentage of
a particular allele
compared to the
total of all other
alleles of the
same gene in a
given population
5. Mutations
A mutation is a change in DNA
sequence that alters the trait a specific
gene controls
• Only one nucleotide pair in a thousand is
randomly changed every 200,000 years
• Some genes control many traits or affect
the expression of many other genes
Caused by:
• Copying errors in the genetic material
during cell division
Deletion
Insertion
Translocation
• Increased by exposure to ultraviolet
or ionizing radiation (x-rays),
chemical mutagens, or viruses
6. Results of Mutation
Results:
• most mutations are neutral
have no effect on
survival/reproduction
• many are harmful
detrimental to fitness or lethal
• VERY small percent are
advantageous
result in a change in phenotype that
improves reproductive success
Cell type matters:
• germ cell (reproductive/sex cell)
mutations are passed on to offspring
• DNA of somatic cells aren't passed
to offspring (mutations stay local)
7. What Changes are Passed On?
Inherited Traits:
• characteristics determined
by genes (DNA)
eye color, height, tongue-
rolling ability
NOT Environmental/Learned Traits:
• things your circumstances teach you
language, how to play piano, love of cheese
8. Adaptations
"Fitness" = an organism's ability
Adaptations are inherited to survive and reproduce
traits that improve help an
organism survive and
reproduce
• "I was born with rugged good
looks and easily found a wife,
even though there were very few
women in the Jamestown colony."
Adaptations are NOT learned
behaviors or characteristics
• "Our family moved to the Alaska
and eventually adapted to the
climate."
9. Adaptation & Environment
A given trait may or may not be an adaptation, depending
on the environment in which the organism lives.
Would these cats' long fur be an adaptation in...
Sahara Desert?
Alaska?
10. Gene Flow
Gene flow occurs when organisms migrate
- new genes are introduced when an organism travels to
join a different population
- only creates
change when
populations are
isolated
• geographically
or
• reproductively
11. Natural Selection
A mutation may improve
"fitness" (chance of
survival/reproduction)
• competition for resources
• health/hardiness
• reproductive success
• predator evasion
Only the fittest (best adapted
to survival) can reproduce
Traits passed on are those with
best adaptations to the current
environment
12. Case Study
White Peppered Moth populations
dwindled and black phenotype
flourished
Assumed bird predation
diminished the less-camouflaged
white moths
Individuals less adapted to their
environment dwindle and may
eventually become extinct
Experiment flaws:
• variables not accounted for:
migration may have affected numbers
time of release, landing behavior, diet
the artificially high numbers released might have
created a predatory magnet
13. Speciation in Darwin’s Finches
In the 1830’s Darwin sailed around the world and
observed incredible diversity in the population of
finches on the Galapagos Islands
14. Galapagos Finch Migration
Natural selection
occurred as the birds
competed for food and
resources.
Adaptations selected
by new surroundings
when they migrated
from mainland to
islands
Geographic and then
reproductive isolation
kept the species distinct
15. Genetic Drift
Random changes in
allele frequency
• random circumstances
cause an allele to become
more common (or extinct)
Freak
Lawnmower
Accident!
What if the
mower-gone-
crazy takes out
all but two rose
bushes, wiping
out all the
recessive
alleles in a
population?
16. Genetic Variation
Evolutionary change
cannot happen without a
change in genes and gene
combinations.
Sources of variation:
• Mutation
• Gene Flow
genetic exchange due to
the migration
without isolation,
reduces differences
between populations
(acts against genetic
variation)
• Sexual Reproduction
17. Meiosis & Genetic Variation
Sexual Reproduction increases genetic variation
• Crossing Over
segments of DNA swap places during prophase 1 of meiosis
• Independent Assortment
chromosomes line up randomly during meiosis
18. Types of Evolution
Microevolution
• small changes within a species'
set of genes that result in
phenotypic differences
• hundreds of years (short time)
Macroevolution
• descent with modification
• the process by which modern
organisms have descended from
ancient ancestors
due to many small
changes over
hundreds of
thousands of
years (long time)
19. Speciation
a lineage-splitting event
that produces two or more
separate species is called
speciation
• produced in lab experiments
• populations change so much that
they no longer can interbreed and exchange genes
• seems to require geographic isolation
Macroevolution = speciation on steroids
Individuals DO NOT evolve over time.
...but POPULATIONS do!
20. Coevolution
Evolution in which two different
species affect each others'
adaptations.
Occurs between organisms that have
close ecological relationships:
• Competitive
fight each other for limited
resources
• Mutualistic
live together in a way that
helps them both survive
easier
• Predator/prey
one hunts/eats the other as
food
• Parasite/host
one lives off the other,
without killing it completely
Notes de l'éditeur
Hardy-Weinberg Equilibrium = p 2 + pq + q 2 = 1
Substitution A substitution is a mutation that exchanges one base for another (i.e., a change in a single "chemical letter" such as switching an A to a G). Such a substitution could: change a codon to one that encodes a different amino acid and cause a small change in the protein produced. For example, sickle cell anemia is caused by a substitution in the beta-hemoglobin gene, which alters a single amino acid in the protein produced. change a codon to one that encodes the same amino acid and causes no change in the protein produced. These are called silent mutations. change an amino-acid-coding codon to a single "stop" codon and cause an incomplete protein. This can have serious effects since the incomplete protein probably won't function. Insertion Insertions are mutations in which extra base pairs are inserted into a new place in the DNA. Deletion Deletions are mutations in which a section of DNA is lost, or deleted. Frameshift Since protein-coding DNA is divided into codons three bases long, insertions and deletions can alter a gene so that its message is no longer correctly parsed. These changes are called frameshifts. For example, consider the sentence, "The fat cat sat." Each word represents a codon. If we delete the first letter and parse the sentence in the same way, it doesn't make sense. In frameshifts, a similar error occurs at the DNA level, causing the codons to be parsed incorrectly. This usually generates truncated proteins that are as useless as "hef atc ats at" is uninformative. There are other types of mutations as well, but this short list should give you an idea of the possibilities.
Six-legged frog - genetic mutation.
Both interact with the environment the organism lives in, but both are not adaptations.
Peppered moth changing color due to adaptation to England’s industrial revolution resulting in blackened tree bark. Kettlewell's experiments were flawed (moths released at wrong time of day, and in numbers creating a possible predatory magnet of the birds). Moths rest not on tree trunks, but under leaves, higher up in the tree canopy. Even so, as the environment changed, so did the phenotypic predominance of the darker species, showing a great example of adaptation (but not evolution). "Industrial melanism"
Species A migrates from the mainland to the first island. Isolated from the mainland, species A evolves to species B. Species B migrates to the second island. Species B evolves in species C. Species C recolonizes the first islands, but is now unable to reproduce with species B. Species C migrates to the third island. Species C evolves into species D. Species D migrates to the first and second island. Species D evolves to species E.
i.e. bugs get stepped on, fire wipes out certain plants, etc.