AP Biology 2004-2005 Chapter 23. Evolution of Populations.
-
Upload
amie-webster -
Category
Documents
-
view
228 -
download
6
Transcript of AP Biology 2004-2005 Chapter 23. Evolution of Populations.
2004-2005 AP Biology
Chapter 23.
Evolution of Populations
2004-2005AP Biology
Populations evolve Natural selection acts on individuals
differential survival “survival of the fittest”
differential reproductive success who bears more offspring
Populations evolve genetic makeup of
population changes over time
favorable traits (greater fitness) become more common Bent Grass on
toxic mine site
2004-2005 AP Biology
Individuals DON’T evolve!!!
2004-2005AP Biology
Mutation & Variation Mutation creates variation
new mutations are constantly appearing
Mutation changes DNA sequence changes amino acid sequence? changes protein?
change structure? change function?
changes in protein may change phenotype & therefore change fitness
2004-2005AP Biology
Sex & Variation Sex spreads variation
one ancestor can have many descendants
sex causes recombination offspring have new combinations
of traits = new phenotypes
Sexual reproduction recombines alleles into new arrangements in every offspring
2004-2005AP Biology
Variation impacts natural selection Natural selection requires a source of
variation within the population there have to be differences some individuals must be more fit than
others
2004-2005AP Biology
Changes in populations Evolution of populations is really
measuring changes in allele frequency all the genes & alleles in a population =
gene pool Factors that alter allele frequencies
in a population natural selection genetic drift
founder effect bottleneck effect
gene flow
2004-2005AP Biology
Natural selection Natural selection adapts a population to
its environment a changing environment
climate change food source availability new predators or diseases
combinations of alleles that provide “fitness” increase in the population
2004-2005AP Biology
Genetic drift Effect of chance events
founder effect small group splinters off & starts a new colony
bottleneck some factor (disaster) reduces population to
small number & then population recovers & expands again
2004-2005AP Biology
Founder effect When a new population is started by
only a few individuals some rare alleles may be at high
frequency; others may be missing skew the gene pool of
new population human populations that
started from small group of colonists
example: white people colonizing New World
2004-2005AP Biology
Distribution of blood types Distribution of the O type blood allele in native
populations of the world reflects original settlement
2004-2005AP Biology
Distribution of blood types Distribution of the B type blood allele in native
populations of the world reflects original migration
2004-2005AP Biology
Out of AfricaLikely migration paths of humans out of AfricaLikely migration paths of humans out of Africa
Many patterns of human traits reflect this migrationMany patterns of human traits reflect this migration
2004-2005AP Biology
Bottleneck effect When large population is drastically
reduced by a disaster famine, natural disaster, loss of habitat… loss of variation by chance
alleles lost from gene pool narrows the gene pool
2004-2005AP Biology
Cheetahs All cheetahs share a small number of
alleles less than 1% diversity as if all cheetahs are
identical twins
2 bottlenecks 10,000 years ago
Ice Age last 100 years
poaching & loss of habitat
2004-2005AP Biology
Conservation issues Bottlenecking is an
important concept in conservation biology of endangered species loss of alleles from gene
pool reduces variation reduces ability to
adapt at risk populations
2004-2005AP Biology
Gene flow Population spread over large area
migrations = individuals move from one area to another
sub-populations may have different allele frequencies
Migrations cause genetic mixing across regions = gene flow new alleles are moving
into gene pool reduce differences
between populations
2004-2005AP Biology
Human evolution today Gene flow in human
populations is increasing today transferring alleles
between populations
Are we moving towards a blended world?Are we moving towards a blended world?
2005-2006 AP Biology
Any Questions??
2004-2005 AP Biology
Chapter 23.
MeasuringEvolution of Populations
2004-2005AP Biology
Populations & gene pools Concepts
a population is a localized group of interbreeding individuals
gene pool is collection of alleles in the population remember difference between alleles & genes!
allele frequency is how common is that allele in the population how many A vs. a in whole population
2004-2005AP Biology
Evolution of populations Evolution = change in allele frequencies
in a population hypothetical: what would it be like if
allele frequencies didn’t change? non-evolving population
1. very large population size (no genetic drift)
2. no migration (movement in or out)
3. no mutation (no genetic change)
4. random mating (no sexual selection)
5. no natural selection (no selection)
2004-2005AP Biology
Hardy-Weinberg equilibrium Hypothetical, non-evolving population
preserves allele frequencies
Serves as a model natural populations rarely in H-W equilibrium useful model to measure if forces are acting on
a population measuring evolutionary change
W. Weinbergphysician
G.H. Hardymathematician
2004-2005AP Biology
Hardy-Weinberg theorem Alleles
assume 2 alleles = B, b frequency of dominant allele (B) = p frequency of recessive allele (b) = q
frequencies must add to 100%, so:
p + q = 1
bbBbBB
2004-2005AP Biology
Hardy-Weinberg theorem Individuals
frequency of homozygous dominant: p x p = p2 frequency of homozygous recessive: q x q = q2 frequency of heterozygotes: (p x q) + (q x p) = 2pq
frequencies of all individuals must add to 100%, so:
p2 + 2pq + q2 = 1
bbBbBB
2004-2005AP Biology
Using Hardy-Weinberg equation
q2 (bb): 16/100 = .16
q (b): √.16 = 0.40.4
p (B): 1 - 0.4 = 0.60.6
q2 (bb): 16/100 = .16
q (b): √.16 = 0.40.4
p (B): 1 - 0.4 = 0.60.6
population: 100 cats84 black, 16 whiteHow many of each genotype?
population: 100 cats84 black, 16 whiteHow many of each genotype?
bbBbBB
p2=.36p2=.36 2pq=.482pq=.48 q2=.16q2=.16
Must assume population is in H-W equilibrium!Must assume population is in H-W equilibrium!
2004-2005AP Biology
Using Hardy-Weinberg equation
bbBbBB
p2=.36p2=.36 2pq=.482pq=.48 q2=.16q2=.16
Assuming H-W equilibriumAssuming H-W equilibrium
Sampled data Sampled data bbBbBB
p2=.74p2=.74 2pq=.102pq=.10 q2=.16q2=.16
How do you explain the data? How do you explain the data?
p2=.20p2=.20 2pq=.642pq=.64 q2=.16q2=.16
How do you explain the data? How do you explain the data?
Null hypothesis Null hypothesis
2004-2005AP Biology
How do allele frequencies change?
Think of all the factors that would keep a population out of H-W equilibrium!
Think of all the factors that would keep a population out of H-W equilibrium!
2004-2005AP Biology
Real world application of H-W Frequency of allele in human population
Example: What % of human population carries allele for
PKU (phenylketonuria) Should you screen prospective parents?
~ 1 in 10,000 babies born in the US is born with PKU results in mental retardation, if untreated
disease is caused by a recessive allele
PKU = homozygous recessive (aa)
2004-2005AP Biology
H-W & PKU disease frequency of homozygous recessive individuals
q2 (aa) = 1 in 10,000 = 0.0001 frequency of recessive allele (q):
q = √0.0001 = 0.010.01 frequency of dominant allele (p):
p (A) = 1 – 0.01 = 0.99 frequency of carriers, heterozygotes:
2pq = 2 x (0.99 x 0.01) = 0.0198 = ~2% ~2% of the US population carries the PKU allele
300,000,000 x .02 = 6,000,000 people
2005-2006 AP Biology
Any Questions??