Natural
Selection
The
Components
of
Natural
Selection
●
Three
conditions
must
be
met
for
natural
selection
to
happen:
○
Variation:
individuals
must
differ
from
one
another
○
Inheritance:
differences
are
inherited
by
offspring
in
the
population
○
Differential
reproductive
success:
individuals
with
certain
traits
are
more
successful
at
surviving
and
reproducing
than
others
●
Mutation
is
one
of
the
major
sources
of
variation
○
Occur
at
random,
independently
of
whether
or
not
they
would
be
favored
●
When
biologists
study
nat
selection,
they
focus
on
how
a
specific
trait
of
interest
changes/remains
constant
over
time
●
Nat
selection
sorts
on
phenotypic
differences,
not
genotypes
○
Need
to
understand
how
genotype
and
environment
interplay
to
influence
phenotype
○
**
genes
code
for
traits
in
the
context
of
a
particular
set
of
environmental
conditions
**
■
Genes
themselves
do
not
code
for
traits
■
This
phenomenon
is
called
norm
of
reaction
■
Ex:
In
4
kinds
of
yarrow
plant,
genotype
1
grows
tallest
at
low
elevation,
but
genotype
4
grows
tallest
at
medium
elevation
EVEN
THO
THEIR
GENES
DON’T
CHANGE
Natural
Selection
and
Coat
Color
in
the
Oldfield
Mouse
(Example)
●
Studies
by
Hopi
Hoekstra
and
colleagues,
coat
color
in
the
oldfield
mouse
●
Hunted
by
visual
predators
such
as
owls
●
Usually
dark
in
coloration,
but
on
Santa
Rosa
Island
off
of
Florida,
they
are
much
lighter
●
Found
that
the
genotypes
of
the
two
mice
differently
expressed
two
genes
that
influence
fur
color
Phylogeny
●
Phylogeny:
shows
which
animals
are
closely
related
●
Parts
of
a
phylogenetic
tree:
○
Nodes:
hypothetical
ancestor
■
Denotes
speciation/seperation
event
○
Branch:
represents
evolution
of
a
lineage
○
Tip:
species,
individual,
other
entity
we
are
studying
■
Aka
Operational
Taxonomic
Unit
(OTU)
●
For
relatedness:
go
by
SHARED
HISTORY ○
More
shared
history
→
more
closely
related
(regardless
of
how
far
away
2
branches
are!)
●
Ancestral
Trait:
trait
in
ancestral
population/species
that
unless
lost
will
be
inherited
●
Derived
Trait:
trait
that
has
changed
state
from
the
ancestral
form
●
Homologous
Trait:
traits
found
in
a
set
of
species
bc
they
are
inherited
●
Analogous
Traits:
traits
found
in
a
set
of
species
but
not
because
of
shared
ancestry
(convergence)
○
Ex:
venomous
fish
have
evolved
at
least
3
times,
but
independently
of
each
other
●
Fun
vocab!
○
Synapomorphy:
shared
derived
trait
○
Homoplasy:
trait
shared
because
of
convergence
■
Ex:
flight
shared
w
birds
and
bees,
but
evolved
independently
○
Plesiomorphy:
ancestral
trait
○
Symplesiomorphy:
shared
ancestral
trait
●
Polytomy:
node
in
the
phylogeny
that
has
more
than
2
descendant
branches
○
Soft
polytomy:
caused
by
uncertainty
○
Hard
polytomy:
very
rapid
speciation
■
Simultaneous
speciation
●
Hybridization
can
complicate
phylogenies
but
don’t
worry
ab
it
:)
Rooting
●
Sometimes
display
trees
w
no
root
●
Showing
relationships
depends
where
root
is!
●
Ingroup:
subgroup
of
interest
in
a
study
●
Outgroup:
one
or
more
species
include
to
provide
direction
in
phylogenetic
study
●
Clade:
branch
of
a
tree
w
one
ancestor
and
ALL
its
descendants
●
When
looking
at
group
of
species,
look
at
most
recent
common
ancestor
(MRCA)
●
Monophyletic:
taxonomic
group
consisting
of
all
descendants
of
the
group’s
MRCA
(and
nothing
else) ●
●
Polyphyletic:
disjointed
group
of
descendants
(BAD)
○
Ex:
taxons
4,
5,
9,
and
10
●
Paraphyletic:
group
that
does
not
contain
all
the
descendants
of
the
group’s
most
common
ancestor
(BAD)
○
Ex:
taxons
6,
7,
1,
and
2
●
Sauropsida:
monophyletic
group
that
includes
all
birds
and
reptiles
(including
dinosaurs)
○
●
Vertebrates:
monophyletic
group
that
includes
fishes,
birds,
mammals,
etc
○
Fishes:
paraphyletic
group
that
doesn’t
include
tetrapods ●
Cladograms:
tree
with
no
info
in
branch
lengths
●
Phylogram:
tree
w
evolutionary
change
represented
as
branch
lengths
●
Chronogram:
tree
w
time
represented
as
branch
lengths
Genetic
Variation
Mendelian
Genetics
●
Law
of
segregation:
every
individual
has
2
gene
copies
at
a
locus,
these
copies
segregate
during
gamete
production
so
only
one
goes
into
a
gamete
○
Only
in
diploids
●
Locus:
physical
location
of
gene
on
chromosome
●
Gamete:
sex
cells
of
organism
●
Allele:
gene
variant
(R
and
r)
●
Law
of
independent
assortment:
allele
passed
for
one
trait
is
independent
of
allele
fro
another
trait
at
another
locus
for
a
gamete
○
Traits
are
randomly
passed
to
offspring
independently
○
Assumes
that
genes
are
unlinked
Genetics
Review!
●
Linkage
disequilibrium:
presence
of
statistical
association
between
allele
at
different
loci
○
Genes
on
same
chromosome
→
potential
that
they
tend
to
be
linked
●
Chromosomal
crossover
and
segregation
produces
gametes
help
produce
novel
allele
combos
in
offspring
○
Begins
link
b/n
geno
and
phenotype
○
Diff
traits
help
in
diff
environments
●
Transcription:
RNA
polymerase
reads
coding
sequence
of
DNA
→
produces
complementary
RNA
and
messenger
mRNA
●
Translation:
mRNA
decoded
by
ribosome
→
amino
acids
→
proteins
●
Codon:
three
nucleotides
(usually
→
amino
acid)
○
Stop
codons
end
translation,
start
codons
start
them
(AUG)
●
Redundancy
in
translation
–
diff
codons
make
same
amino
acid
○
Ex:
CUU,
CUC,
CUA,
and
CUG
all
code
for
Leucine
●
RNA
polymerase
binds
to
promoter
region,
signals
where
to
begin
transcription
●
Introns
not
encoded
into
proteins
but
can
serve
important
regulatory
functions
or
provide
spacing/secondary
structure
●
Exons
encoded
into
proteins
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller gloriakawai. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $15.49. You're not tied to anything after your purchase.
