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6/15/2016
Lecture 7
Microevolution
Microevolution
1.
2.
3.
4.
5.
What causes evolution?
Allele frequencies: A critical measure
Gene flow
Non-random mating
Genetic drift
What is an allele frequency?
Population = a group of individuals from a single species
Genes are all the same, but alleles probably differ
Mutations
1.
2.
3.
4.
5.
How do codons get read?
Incorrect readings: a variety of point mutations
Chromosome level mutations
Aneuploidy and polyploidy
Causes and effects of mutations
Microevolution
What is an allele frequency?
Allele frequency is simply the number of times an
allele occurs in the population.
Frequencies are represented as a proportion of the
whole (typically in decimal form).
Tongue rolling:
Ability to roll = RR or Rr
Inability to roll = rr
Microevolution
How do allele frequencies change?
1.
2.
3.
4.
5.
Gene flow
Non-random mating
Genetic drift
Mutation
Selection
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Microevolution
Microevolution
Gene flow
Gene flow
Microevolution
Microevolution
Non random mating
Non random mating
Assortative mating:
Organisms of similar phenotype
mate more often than expected
by random chance
Tends to increase the frequency
of homozygotes in the
population
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Microevolution
Non random mating
Microevolution
Genetic Drift
Microevolution
Genetic Drift
Microevolution
Genetic Drift
Drift is all about sample size!
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Microevolution
Mutations
Mutation
RNA codes for particular amino acids
Mutation is the ultimate
source of all genetic
variability
Mutations
Mutations
The codes for amino acids are degenerate
Francis Crick and Sydney Brenner
determine how codons are read
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Mutations
Deletion only disturbs one word
Mutations
Single or double deletions
Mutations
Deletion skews all “downstream” words
Mutations
Triple deletions
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Mutations
C
AUGUAUGCUCCGAAU
Mutations
* Codons are read in threes
* Codons are not spaced
* Reading frame is critical
AUGAUGCUCCGAAU__
AUGCUAUGCUCCGAAU
Francis Crick and Sydney Brenner
Frameshift mutation via addition
Mutations
Orig seq = TACACCGAGGGCCTAATT
Mutations
Orig seq = TACACCGAGGGCCTAATT
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Mutations
Orig seq = TACACCGAGGGCCTAATT
Mutations
Frameshifts
Silent muations
Point mutations
Missense
Nonsense
Mutations
Mutations
Also see Life 10e Fig 15.4
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Mutations
Mutations
Also see Life 10e Fig 15.4
Mutations
Also see Life 10e Fig 15.4
Mutations
Meiosis 1 (the first division)
Nondisjunction:
occurs when
chromosomes fail to
separate during
Metaphase 1
Normal meiosis: Chromosomes
have regular disjunction and
separate into daughter cells
Aneuploids:
have gained or lost
a chromosome
Also see Life 10e Fig 15.4
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Mutations
Mutations
22
22
23
23
Monozomy
Monozomy
Mutations
Mutations
Chromosomes 13, 15, 18, 21, 22 can be doubled
and lead to individuals that survive for a time
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Trizomy
Normal karyotype
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Mutations
Trisomy 21 karyotype
Mutations
Aneuploidy is very common
in sex chromosomes
Mutations
Mutations
Ploidy = number of copies of chromosomes
Aneuploidy is thought to be very common
More than two copies = polyploid (xN)
Banana plants come in
many ploidy levels:
2N= 22
4N = 44
5N = 55
7N = 77
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Mutations
Mutations
Four causes:
* Ionizing radiation
* Chemical mutagens
* Exposure to some viruses
* Spontaneous mutation during
replication
Mutations
Three outcomes:
* Beneficial
* Harmful
* Neutral
* Beneficial
Mutations
Lethal
* Harmful
* Neutral
Three outcomes:
Three outcomes:
* Harmful
Minor to major effects
* Neutral
Silent
Non-coding
* Beneficial No fitness loss
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Mutations
Three outcomes:
* Harmful
* Neutral
* Beneficial
Natural selection
Lecture 8
Natural Selection
1.
2.
3.
4.
5.
6.
The only adaptive evolutionary force
Stabilizing selection
Directional selection
Disruptive selection
Balancing selection
Determining fitness
Sexual selection
1.
2.
3.
4.
5.
Males and females have different reproductive strategies
Females choose…
…most of the time (when the exception proves the rule)
Males compete
Females gain by their choosiness
a. Co-parents
b. Territory
c. When males don’t stick around – theories!
Natural selection
Grant and Grant
Can you think of an example of a
bottleneck event that we’ve already
discussed in class?
Did the finches go through a bottleneck?
Did genetic drift change their beak size?
from P. T. Boag and P. R. Grant in Science 214:82, 1981
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Natural selection
Natural selection
What force changed the finch’s beaks?
Factors required for natural selection to
operate:
1. There must be variation in the
population
2. Variation must lead to
differences among individuals
in lifetime reproductive success
3. Variation must be transmitted to
the next generation
Natural selection
Natural selection
Factors required for natural selection to
operate:
1. There must be variation in the
population
2. Variation must lead to
differences among individuals
in lifetime reproductive success
Generation 1
3. Variation must be transmitted to
the next generation
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Natural selection
Selection is the only adaptive evolutionary force
Natural selection
Common selective forces:
1.
2.
3.
4.
5.
6.
But what can adapt?
Natural selection
Predation is a strong selective force
Predation
Climatic factors
Parasitism
Mate attraction
Resource acquisition
More!
Natural selection
Predation is a strong selective force
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Natural selection
Natural selection
Absolute fitness
Relative fitness
Relative
fitness =
3/3 or 1
Fitness = 3
Generation 1
Generation 1
Relative
fitness =
1/3 or .33
Fitness = 1
Natural selection
Stabilizing selection
Natural selection
Directional selection
Bella coola
Directional selection by fishing on pink
salmon Onchorhynchus gorbuscha
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Natural selection
Natural selection
There’s one other type of selection:
Balancing selection
Disruptive selection
Agrostis tenuis
Mine
Index of tolerance
Nonmine soil
1. Heterozygote advantage
2. Negative frequency dependent selection
0
50
100
150
Distance in meters
Natural selection
Natural selection
Balancing selection
Heterozygote advantage
Balancing selection
Negative frequency dependent selection
Relative fitness
AA - .75
Aa – 1
aa - .25
A sickled blood cell
Relative fitness
Common
.65
Rare
1
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Natural selection
Balancing selection question:
Sexual selection
Sexual selection
Evolution is all about mating
Sexual selection
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Sexual selection
Reproductive Strategy
Mate choice
Mating frequency
Mate guarding
Long-term mating behavior (monogamy vs. polygyny)
Parental care
Offspring spacing
Sexual selection
Females are choosy!
Sexual selection
Darwin notes:
Females often do
not mate with the
first male they see.
They evaluate.
Sexual selection
Energy
Human eggs are 195,000X
larger than sperm and
contain far more nutrients.
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Sexual selection
Sexual selection
Time
Purely mathematical
Females cannot have as many offspring as males
Gestation limits new
mating opportunities
Maternal care takes time
Sexual selection
Sexual selection
Take home message:
For males, sex is cheap.
For females, the after effects can be
VERY costly.
Take home message:
For males, sex is cheap.
For females, the after effects can be
VERY costly.
Sexes differ in parental investment
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Sexual selection
Sexual selection
Some males stick around!
So if females choose, what
do males do?
Sexual selection
Male riflebird
Female riflebird
http://news.nationalgeographic.com/news/2007/02/070221-riflebird-video.html
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Sexual selection
Sexual selection
Sexual dimorphism
What are the females getting by being choosy?
Good dads
Sexual selection
Sexual selection
What are the females getting by being choosy?
What about absent fathers?
Resource protection
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Sexual selection
Sexual selection
1. Oldest
2. Largest
3. Healthiest
GOOD GENES
Handicap principle
Sexual selection
Sexual selection
Runaway selection
Runaway selection
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Sexual selection
Natural selection will slow runaway sexual selection
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