Transcript 2 evolution notes 2013

Evolution- “Change Over Time”

All of the changes that have occurred in living things
since the beginning of life on Earth
Darwin vs. Lamarck
Lamarck
Darwin
Jean-Baptiste LaMarck

French, Early 1800’s
Theory of
Inheritance of
Acquired Characteristics

Two main points…
1. Principle of Use & Disuse:

Most used body structures develop, unused
structures waste away
2. Inheritance of Acquired
Characteristics:
•
Once the structure is modified, the new
trait can be inherited (passed to
offspring)
Explain the picture below as if you
were LaMarck…
Why we don’t believe him…
• Experiments: show that changes
that occur in an animal’s life are not passed on
to its offspring
Genetics
:
Gregor Mendel discovered
that traits are passed down through GENES
(which aren’t affected by the outside world in
that way)
Charles Darwin
“The Father of Evolution”
 1831-
sailed on the HMS Beagle to
the Galapagos Islands.
 Studied many species of finches.
 Published book in 1845:
 “On the Origin of Species by
Natural Selection”
Darwin’s Theory of
Evolution
(don’t copy all this it’s on your handout) 
“Natural Selection”
“Survival of the Fittest”
Natural Selection

Process by which favorable heritable traits
become more common in successive
generations of a population of reproducing
organisms, and unfavorable heritable traits
become less common.
Natural Selection
Four main points…

1. More organisms are produced than can
survive…leads to COMPETITION OVER
RESOURCES

Ex’s of resources…




Water
Food
Habitat
Mates
2. Individuals within a population
vary, and some of these traits are
heritable.
3. Some variations are FAVORABLE
(increase chances for survival/ reproduction)


Male vs. Female
Cardinals
Male color attracts
female=
reproductive
advantage
4. Better adapted individuals
survive and reproduce


These are the individuals that will pass on
their genes to the next generation.
This can change the GENE POOL:

Includes all the genes of every reproductive
member of a population
What The theory of evolution IS
NOT!!!




It does NOT occur in INDIVIDUALS…only
populations!
It does NOT happen quickly…the Earth has
a Looooooong history!
It does NOT explain how life came to be on
Earth, just how it evolved after it was here.
It does NOT have any driving force except
the competition for limited resources.
Species…

A group of organisms that are genetically
similar enough to produce healthy, fertile
offspring.
Darwin’s Finches
An example of Adaptive Radiation
The Galapagos Islands
Finch Types:
Using Darwin’s
Theory, explain how all
of these different
species evolved.
Darwin…one smart guy…
“Seeing this gradation &
diversity of structure in
one small, intimately
related group of birds,
one might really fancy
that from an original
paucity of birds in this
archipelago, one species
had been taken and
modified for different
ends.”
Phylogenetic Trees


Show evolutionary “relatedness”
Based on fossil record, dna evidence, structural
similarity, etc
What common ancestor do all of
These organisms share?
Darwin’s Finches…again…
What common ancestor do
the seed eating and cactus
eating finches share?
What do each of the finch
pictures on here represent?
Which 2 species are more
closely related:
a. Mangrove Finch and
Woodpecker finch
b. Small ground finch and
Bud-eating finch
Good Questions with Good Answers.

How can new species be formed and the
old one not go extinct? Wasn’t the whole
reason a new species formed was that it
had a survival advantage?
Speciation does NOT necessarily
cause EXTINCTION!

A NEW SPECIES’ existence just means…

That POPULATION’S GENES have been
altered so much that they can no longer mate
with members of the original population.


NOW there are TWO SPECIES
Eventually…one may go extinct, but NOT
NECESSARY!!!
Darwin’s Finches…p 558

Illustrate SPECIATION: when a species
breaks into two (or more)

The organisms in the two species can no
longer…

INTERBREED
 What
could cause this to
happen?




Occupy a new niche/habitat
Geographic barriers/Reproductive Isolation
Reduction of gene flow
Selective Pressure
Geographic Isolation…
Sometimes populations
are spit In two due to a
geographic barrier. This
can lead to reproductive
isolation. How could this
lead to speciation?
Reduction of Gene Flow…
If members of a species live far away from each other, they will have a
decreased chance of mating. This would create reduced gene flow, but not
total isolation. Speciation would probably also require different selective
pressures at the two ends.
Eventually, this could
alter gene frequencies in
groups at different ends
of the range so much that
they would not be able to
mate if they were
reunited…that’s
speciation!
Selective Pressure


A “pressure” from the environment that
makes some individuals more likely to
survive and reproduce.
Three types…



Disruptive
Directional
Stabilizing
Types of Natural Selection

Stabilizing Selection

Occurs when natural selection works against the
2 extremes of a trait to make the population more
uniform.
Stabilizing Selection
Stabilizing Selection

Birth weight of babies

Babies that are too big or too small might have
less chance of being born healthy.
Natural Selection

Directional Selection

Selects the extreme of 1 trait.
Directional Selection

In a population of plants, flowers with the
brightest color might be selected for in
order to attract the most pollinators.
Natural Selection

Disruptive Selection

Selects against the mean of the population.

Disruptive Selection
If there are 2 types of seeds to eat for a
population of birds, either of 2 different beak
shapes (sharp or blunt) might be selected for,
but a beak that’s the average of the 2 shapes
might not be particularly good at eating either
seed, so it would be selected against.



Evolution occurs over MANY generations
Evolution occurs within POPULATIONS
(NOT individuals)
Evolution involves genetic changes in a
SPECIES

(Members of a species interbreed to produce
healthy, fertile offspring)
The process by which favorable heritable traits
become more common in successive generations of a
population of reproducing organisms, and
unfavorable heritable traits become less common.
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Evolution
Natural Selection
Adaptations
Genetic
Recombination
Ev
1.
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25% 25% 25% 25%
Consider, for example, a population of shellfish called limpets. The shell color
of these limpets ranges from white, to tan, to dark brown. As adults, limpets
live attached to rocks. On light-colored rocks, white-shelled limpets have an
advantage because their bird predators cannot easily see them. On darkcolored rocks, dark-colored limpets have the advantage because they are
camouflaged. On the other hand, birds easily see tan-colored limpets on either
the light or dark backgrounds. These tan-colored limpets will be at a selection
disadvantage and will most likely become extinct from the population. This
type of natural selection is known as:
33%
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33%
Stabilizing Selection
Directional Selection
Disruptive Selection
St
ab
1.
33%
Consider a population of spiders in which the average size
is a survival advantage. Predators in the area might easily
see and capture spiders that are larger than average.
However, small spiders may find it difficult to find food.
Therefore, in this environment, average-sized spiders are
more likely to survive. This type of natural selection is
known as:
33%
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33%
Stabilizing Selection
Directional Selection
Disruptive Selection
St
ab
1.
33%
Imagine a population of woodpeckers pecking holes in trees to
feed on the insects living under the bark. Suppose that a species of
insect that lives deep in tree tissues invades the trees in a
woodpecker population’s territory. Only woodpeckers with long
beaks could feed on that insect. Therefore, the long-beaked
woodpeckers in the population would have a selective advantage
over woodpeckers with very short or average-sized beaks. This
type of natural selection is known as:
33% 33% 33%
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Stabilizing Selection
Directional Selection
Disruptive Selection
St
ab
1.
The smallest unit that can evolve is:
25% 25% 25% 25%
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A genome
An individual
A community
A population
A
1.
To predict evolutionary activity, we look at
the population’s Gene Pool

Gene pool - all the genes of every
reproductive member of a population.
Genetic Equilibrium


Not all populations are in an active state
of “natural selection”
GENETIC EQUILIBRIUM

This means that there is no change in the gene
pool = no evolution
Genetic Equilibrium


1.) Population size is large
2.) No gene flow in the population



3.) No mutations
4.) No environmental factors causing
natural selection


No new organisms introducing more alleles
No trait is favorable over another
5.) Random mating must occur
So what factors exist to make a
population evolve?


It must NOT be in GENETIC
EQUILIBRIUM
Something that knocks the population
out of genetic equilibrium is called a
MECHANISM OF EVOLUTION
Mechanisms of
Evolution
Sources of Genetic Variation

What do you think are some sources of
genetic variation?
Mechanisms of Evolution





1.
2.
3.
4.
5.


Natural Selection
Sexual Selection / Non-random mating
Mutation
Gene Flow (Migration)
Genetic Drift- reduces population size
Bottleneck effect
Founder effect
Genetic Drift
Genetic Drift occurs when the
frequency of alleles change
due to
RANDOM PROCESSES!
(NOT natural selection)
Genetic Drift
Natural Selection vs. Genetic Drift
Genetic Drift

http://www.biology.arizona.edu/evolution/ac
t/drift/frame.html
Kinds of Genetic Drift…
Bottleneck Effect
Bottleneck Effect
Bottleneck Effect
Another kind of Genetic
Drift…Founder Effect
What term(s) would best describe the
picture below.
24%
1.
76%
2.
0%
3.
0%
4.
Founder Effect
Bottleneck Effect
Ross Effect
Mutation
Original Population
Newly Established Population
What term(s) would best describe the
picture below.
25%
1.
25%
2.
25%
3.
25%
4.
Pizza effect
Bottleneck effect
Founder effect
Woods effect
Evolution Rewind

If a large population of the same species of
squirrels were fed nuts that come from
plant containing a toxin that is poisonous to
the squirrel, the researcher concludes that
these squirrels die and cannot survive on
these nuts alone. Then the researcher
introduces the poisonous nuts to a smaller
isolated population of the same species of
bird and finds that these birds are able to
eat the nuts. How can this be explained?

Recently West Nile Virus has become a
major problem in our area. Cities have
begun spraying pesticides in the
summertime to try and kill off a large
amount of mosquitoes. How come every
few years the cities should change their
pesticide mix?
Population
Genetics
Relative Frequency of an Allele



The number of times an
allele occurs in the gene
pool, given as a percentage
Relative frequency has
nothing to do with dominant
or recessive
The recessive allele can
occur more frequently
How does reproduction affect
natural selection

Discuss with your partner:

How would a population that
reproduces asexually “evolve”
differently than one that
reproduces sexually? WHY?
A note on sexual reproduction…



Sexual reproduction can produce many
different phenotypes
Sexual reproduction does NOT change
relative frequency of alleles in a population
Think about shuffling a deck of cards


Shuffling cards gives you different hands
It won’t change the number of kings in a deck
Population Genetics

In the early 1900s these two men
discovered how the frequency of a trait’s
alleles in a population could be described
mathematically.
G H Hardy – British Mathematician
Wilhelm Weinberg – German Doctor
Population Genetics

For every phenotype how many alleles do
you have???

2


1 from Mom and 1 from Dad
These scientists figured out an equation
that can be used to figure out the
percentages of alleles and genotypes that
are in a population.
Genetic Equilibrium:
Hardy-Weinberg Principle


Allele frequency in a population
will remain constant unless an
outside factor causes those
frequencies to change
When allele frequencies remain
constant, we call this genetic
equilibrium
Population Genetics Background

Given a population of 300 plants…


How many total height genes are there?
Given that 100 plants are short (recessive trait),
200 are tall, and 50 are homozygous tall, how
many are there of each genotype?




How many T alleles are there in the gene pool?


Homozygous recessive
Homozygous dominant
Heterozygous
What is this alleles’ frequency in the population?
How many t alleles are there in the gene pool?

What is this alleles’ frequency in the population?
Genetic Equilibrium Review

In order for their equation to work the
population has to be in GENETIC
EQUILIBRIUM

This means that there is no change in the gene
pool = no evolution
Genetic Equilibrium (Review)


1.) Population size is large
2.) No gene flow in the population



3.) No mutations
4.) No environmental factors causing
natural selection


No new organisms introducing more alleles
No trait is favorable over another
5.) Random mating must occur
The Hardy-Weinberg Equation




p2 + 2pq + q2 = 1
p2 = frequency of the homozygous
dominant genotype
2pq = frequency of the heterozygous
genotype
q2 = frequency of the homozygous
recessive genotype
Hardy-Weinberg




p – frequency of the dominant allele
q – frequency of the recessive allele
Because there are only 2 alleles, the
frequency of the dominant allele (p) and the
frequency of the recessive allele (q) will
add up to 1 or 100%
p+q=1
Hardy-Weinberg


In reality, no population satisfies the HardyWeinberg equilibrium completely
However, in large populations with little
migration and little natural selection, it can
approximate gene frequencies
Hardy-Weinberg Example

In a population of 100 people 28 of them were
found to have freckles and 72 were not. We learned
in class during our genetics unit that having freckles
is a recessive trait and not having them is because
of a dominant trait. If this population is in genetic
equilibrium then solve for the allelic frequencies and
the variables in the hardy-weinberg equation:
How does reproduction affect
natural selection

Discuss with your partner:
How would a population that reproduces
asexually “evolve” differently than one that
reproduces sexually? WHY?

A note on sexual
reproduction…



Sexual reproduction can produce many
different phenotypes
Sexual reproduction does NOT change
relative frequency of alleles in a
population
Think about shuffling a deck of cards


Shuffling cards gives you different hands
It won’t change the number of kings in a deck
Queens full of Jacks!



Let’s Mate!
red card=dominant allele=R
black card=recessive allele=r
P2 + 2pq + q2
Prediction
1st gen.
2nd gen
3rd gen
RR
Rr
rr
36%
48%
16%
Predicted vs Actual

If this population is in equilibrium, we
should have the predicted % for our
genotypes…

We have…20 rr envelopes and 30RR
envelopes
Are we in equilibrium?

What should happen?
If we are evolving…
If we are not…
If a population is in genetic equilibrium and 30% of the
individuals are homozygous recessive for the trait of
color, what is the percentage of homozygous dominant
individuals?
.30
.55
.45
.20
.50
4.
5.
.3
1
2
3
4
5
6
7
8
21
22
23
24
25
26
27
28
9
10
11
12
13
0%
.5
5
0%
14
15
0%
16
0%
0%
17
18
.5
3.
.2
2.
.4
5
1.
19
20
If a population is in genetic equilibrium and 41% of the
individuals are homozygous recessive for the trait of
color, what is the percentage of homozygous dominant
individuals?
.13
.36
.45
.64
.50
4.
5.
1
2
3
4
5
6
7
8
21
22
23
24
25
26
27
28
9
10
11
12
13
0%
.3
6
.1
3
0%
14
15
0%
16
0%
0%
17
18
.5
3.
.6
4
2.
.4
5
1.
19
20
Using the example of the west nile mosquitoes that are sprayed
with a pesticide, suppose one mosquito has a genetic mutation
that allows the mosquito to survive. Which graph best represents
the frequency of this gene over time?
2
3
4
5
6
7
8
21
22
23
24
25
26
27
28
9
10
11
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13
14
ct
u
16
C
re
re
C
ho
i
ce
4
0%
ho
i
ce
15
Pi
Pi
ct
u
re
C
ho
i
ce
ho
i
C
re
ct
u
Pi
1
0%
2
0%
1
0%
3
4.
ct
u
3.
ce
2.
Pi
1.
17
18
19
20
You have determined the frequency of the dominant
allele in a population. Over the next two generations,
the frequency of this allele does not change. Which
factors below must be true in order to maintain this
equilibrium:
20%
1.
20%
2.
20%
3.
20%
4.
20%
5.
Random mating
Large population size
No natural selection
No gene flow
No mutations
The frequency of a particular recessive allele in a
population of chipmunks is .3
The frequency of the dominant allele in this same
population is:
25%
1.
25%
2.
25%
3.
25%
4.
.3
.6
.7
1
1
2
3
4
5
6
7
8
21
22
23
24
25
26
27
28
9
10
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13
14
15
16
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18
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