Download AP Biology – Ch. 23 – The Evolution of Populations

AP Biology – Ch. 23 – The Evolution of
Populations
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The smallest unit of evolution?
Microevolution
3 main mechanisms responsible for change in
allele frequency
Which one of these consistently improves the
match between organisms and their environment?
Microevolution
Microevolution
Microevolution
Microevolution
Five Fingers of Evolution
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https://www.youtube.com/watch?fe
ature=player_embedded&v=5NdMnl
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23.1
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How do the variations that are the
raw material for evolutionary
change arise?
Mutation and sexual reproduction
Genetic Variation
A) Variation Within a Population
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Discrete or quantitative
Either-or-basis vs on a continuum
Single gene vs two or more genes
Measuring Genetic Variation
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Gene variability vs nucleotide
variability
Average heterozygosity – gel
electrophoresis, restriction fragment
analysis
Nucleotide variability – compare
DNA sequences
Why is this information important?
Variation between populations
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Geographic variation-differences in
the genetic composition of separate
populations
Ex) mice populations separated by a
mountain range, mummichog fish
and a cold-adaptive allele(cline)
Mutation
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The ultimate source of new alleles
Change in the nucleotide sequence
of an organism’s DNA
Point mutation
Alter gene number or sequence
Mutation rates – low in plants and
animals
- even lower in prokaryotes and
viruses(but shorter generation time)
- RNA viruses – mutations accumulate
faster – how does this impact treatment?
Sexual Reproduction
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variation results from the unique
combination of alleles that each
individual receives due to:
- crossing over
- independent assortment
- fertilization
23.2 – Hardy-Weinberg
-population
-gene pool/fixed allele
-conditions for HW equilibrium?
1. no mutations
2. random mating
3. no natural selection
4. extremely large population
5. no gene flow
23.3
Natural selection, genetic drift, and gene flow – alter
allele frequencies directly
1. natural selection – favoring some alleles over
others can result in adaptive evolution
2. genetic drift – chance events causing allele
frequencies to fluctuate
a. founder effect – Ex) Tristan da Cunha
b. bottleneck effect – a severe drop in
population size due to a change in the
environment
- case study – prairie chickens
Genetic drift: A Summary
1.
2.
3.
4.
significant in small populations
can cause allele frequencies to
change at random
can lead to loss of genetic
variation within populations
can cause harmful alleles to
become fixed
Gene Flow
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the transfer of alleles into or out of
a population due to movement of
fertile individuals or gametes
serves to reduce genetic differences
between populations
Fig. 23.12 – Agrotis tenuis – What
if?
Modes of selection
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http://wps.pearsoncustom.com/wps
/media/objects/3014/3087289/Web
_Tutorials/17_A02.swf
Sexual Selection
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A form of natural selection in which
individuals with certain inherited
characteristics are more likely than
other individuals to obtain mates
http://evolution.berkeley.edu/evosit
e/evo101/IIIE3Sexualselection.shtm
l
http://www.pbs.org/wgbh/evolution
/library/01/6/l_016_09.html
The Preservation of Genetic
Variation
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1. Diploidy
2. Balancing Selection
a. Heterozygote Advantage
b. Frequency-dependent
selection
3. Neutral Variation
Frequency-Dependent Selection
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Situation 1 – Butterfly mimics poisonous butterfly
Situation 2 - Poisonous butterfly has several
morphs
Situation 1 – The fitness of the mimics is
positively/negatively frequency-dependent – The
fitness of a genotype increases as it becomes
more/less frequent.
Situation 2 – The fitness of each morph is
positively/negatively frequency-dependent – Each
morph gets fitter as it becomes more/less common.
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