Evolution and Speciation

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Evolution and Speciation
Darwin's Principles of Natural Selection 1)
Variations exist in every group of animals
and plants. 2) More offspring are
produced than survive. Some always die.
3) Individuals that survive pass on their
genes to their offspring. survival of
the fittest
populations tend to get rid of deleterious
mutations genes that provide an advantage become
more common in a group
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Evolution and Speciation
evolution change in genotype frequency over
time speciation development of separate
populations over time 2 types of
speciation anagenesis change of a population
in a single location over time such that the
current and past species are
distinct cladogenesis change of a portion
of a population into a new form while the
original population continues to co-exist
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Evolution and Speciation
biological speciation developed by Darwin,
animals that cannot produce fertile offspring
(ie. horses and donkeys-- mules are
sterile) morphological speciation working
definition where animals that cannot be
tested for interbreeding based on similar
features and structures
biological speciation
morphological speciation
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Mechanisms of Speciation (Cladogenesis)
for 2 species to become separate, they must
become unable to interbreed ie. they must
exist in reproductive isolation 4 separate
mechanisms 1) environmental ie geographic,
temperature, habitat, rivers, etc 2)
behavioral ie mating display, timing of
reproduction, etc 3) mechanical (you'll just
have to imagine this one...) 4) physiological
ie. translocations, sperm receptors, etc
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Mechanisms of Speciation (Cladogenesis)
allopatric speciation speciation caused by
physical factors hybrid zone location where
two populations can interbreed but result in
less competitive offspring than when mating
within their own group parapatric speciation
speciation caused by movement into a new
habitat sympatric speciation when a
polymorphism develops that leads to
speciation ie. a polymorphism opens up a new
habitat to live in
sympatric
parapatric
allopatric
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Mechanisms of Speciation (Cladogenesis)
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Darwin's finches adapted to their new environment
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Modes of Speciation (Cladogenesis)
phyletic gradualism slow change of species over
time Darwin's expectation- organisms adapt to
better fit their environment punctuated
equilibrium short bursts of change followed by
long periods of equilibrium punctuated
equilibrium is the more recent theory requires
rapid change (ie. new environment) rare
alleles become more common so that a new
equilibrium is reached Hardy-Weinberg models
suggest populations should reach an
equilibrium eventually
punctuated equilibrium
phyletic gradualism
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Evolution and Speciation
polymorphism difference in DNAs that occur in
more than 5 of the individuals in a
population- 5 is used to separate new
mutations originally thought that polymorphisms
were uncommon and rare first identified by
SDS-PAGE 39 of 18 proteins examined were
polymorphic, and each individual averaged
being heterozygous at 12 of loci expanding
those numbers out to 25,000genes 10,000
genes in humans are polymorphic EACH person is
heterozygous for 3000 (!!!) genes
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Heterozygous Advantage
heterozygote advantage where both homozygotes
are less fit than the heterozygote-- classic
example is sickle cell anemia sickle cell
hemoglobin heterozygotes are resistant to
malaria if selection conditions are changed, the
advantage can go away Africans have a high
level of malaria and frequent heterozygotes
African-Americans have little malaria and a
reduced allele frequency loss of selective
advantage allows elimination of the disease
allele genetic load loss of individuals in a
population to keep heterozygosity
The newt Triturus cristatus is one example
of heterozygous advantage where
heterozygotes mate and all the homozygotes die
off, leaving only the heterozygotes
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Frequency Dependent Selection
in most conditions we've studied, selection
coefficients are constant not always the
case frequency dependent selection where
selection depends upon the frequency of the
phenotype in a given population if the
environment changes or is variable (including
population density) different combinations of
alleles may have a selective advantage soft
selection where frequency and/or population
density matters example ability to feed on
seeds or fruits if everyone feeds on fruit, the
selection is more intense, but if few feed on
fruits, it is easier for those individuals to
find food
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Molecular Evolution
If DNA changes over time, we should see those
differences by sequencing various
organisms evolutionary clock accumulation of
mutations at a constant rate NOT necessarily
protein changes silent mutations can add
up organisms separated most recently in the
past should have the most similar DNA
sequences the more distantly they are related,
the less closely their sequences phylogenetic
tree diagram showing the relatedness of various
species
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Molecular Evolution
the phylogenetic tree made using molecular
similarity can be tested functional amino acids
in proteins should be completely conserved
these should not change over time as the protein
would fail to work other regions of the DNA
(regulatory DNA, inactive transposons,
introns,wobble base of codons, etc) may allow
more variation non-coding region of DNA make
better clocks different strains of flu
(influenza) are related
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Mitochondrial Genetics
so far, we've almost exclusively considered
nuclear genes mitochondria have DNA as well-- it
is replicated, inherited, etc as well maternal
inheritance mitochondrial DNA is essentially
only from the egg-- female line only
different from sex linked genes in the
nucleus like other DNA, mitochondria
accumulate mutations over time more related
individuals will have more similar mitochondria
eve theoretical original human mother that
contributed the first mitochondrial DNA
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Mitochondrial Genetics
most recent common ancestor what is the earliest
ancestor in the phylogenetic tree which is
where the 'divergence' occurred mitochondrial
DNA in african populations is much more diverse
than anywhere else in the world (ie. rare
mutations have been kept) 3 of 4 major
mitochondrial DNA lineages are found only in
Africa the most recent common ancestor of
africans/non-africans was 50,000 years ago
(/- 25,000 years) note the relatively poor
estimation of time archeology dates the 'Great
African migration' to 100,000 years
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Mitochondrial Genetics
note the earliest migrations visible were in
africa all the rest occurred later from one or
more pathways at different times later
migrations gave mitochondrial DNA similar to the
other location
mitochondrial DNA can show the path of early
human migrations