Lecture
1:
The
Genetic
Approach
to
Biology
Pre-Lecture
Notes
Detective
Work:
Figuring
Out
What
Genes
Do
●
Genes
carry
essential
genetic
information
○
Geneticists
try
to
figure
out
what
particular
genes
do
and
how
they
affect
the
organism
as
a
whole
●
Human
genome:
~20,000
protein-coding
genes,
~63,000
total
genes
●
Gene
discovery:
search
for
genes
w/
specific
functions
●
Method
(called
forward
genetics
):
choose
a
phenotype/character/trait
of
interest,
search
for
genes
that
affect
that
trait
○
Usually
start
by
comparing
wild-type
individual
to
variant
using
genetic
crosses
●
Modern
tech
+
long
history
of
research
→
complete
genome
sequences
available
for
humans
and
other
species
→
another
method
is
to
choose
an
unknown
piece
of
DNA
and
work
backwards
to
see
how
it
affects
an
organism
(
reverse
genetics
)
●
Mutations
appear
spontaneously
in
the
wild
○
If
variant
individual
is
rare,
called
mutant
or
mutation
○
Mutants
can
also
be
created
in
lab
using
mutagenesis
,
where
organism
is
exposed
to
environment
that
will
speed
up
rate
of
DNA
mutation
●
Mutants
studied
in
order
to
determine
consequences
of
altering
a
gene,
to
follow
gene
inheritance
b/n
generations
○
When
disrupted
gene
in
a
mutant
is
identified,
usually
named
for
the
mutant
phenotype
■
Ex:
gene
disrupted
in
flies
that
lack
wings
is
called
wingless
●
Genetic
dissection:
gene
discovery
using
collections
of
mutants
that
affect
trait
of
interest
Tools
for
Genetic
Analysis
●
Gel
electrophoresis:
uses
electric
field
to
separate
DNA,
RNA,
or
protein
pieces
by
size,
shape,
charge
●
Band:
molecules
of
same
size
appear
as
a
band
in
the
gel
○
Assumes
that
there
are
many
copies
of
the
molecule
○
Single
molecule
can’t
be
depicted
in
the
gel
●
Ladder:
reference
sample
for
which
the
sizes
of
the
molecules
are
known
●
Polymerase
Chain
Reaction
(PCR):
method
that
allows
for
copying/amplifying
specific
DNA
sequences Chapter
1:
The
Molecular
Basis
of
Heredity,
Variation,
and
Evolution
1.1
Modern
Genetics
Is
in
Its
Second
Century
●
Germ
Plasm
Theory:
reproductive
organs
carry
full
sets
of
genetic
info
w/in
the
sperm/egg
cells,
which
are
brought
together
in
fertilization
●
Four
phases
of
modern
genetics:
○
Identification
of
cell/chromosome
basis
of
heredity
○
Identification
of
DNA
as
hereditary
material
○
Description
of
informational/regulatory
processes
of
heredity
■
Encoding
info
in
genes
■
Transcription/translation
○
Genomic
era
■
Current
■
Began
in
80s
w
completing
first
genome
sequences,
continues
to
now
●
Genes:
physical
units
of
heredity
○
Made
up
of
DNA
sequences
that
contain
info
to
produce
RNA
molecules
●
Chromosomes:
long,
single
molecules
of
double-stranded
DNA
bound
by
many
kinds
of
proteins
○
Chromosomes
in
sexually
producing
organisms
usually
are
in
homologous
pairs
(homologs)
○
Carries
many
genes
●
Bacteria
and
archaea
have
one
circular
chromosome
→
only
one
copy
of
each
gene
in
in
the
genome
(condition
called
haploid
)
○
Bound
by
small
amount
of
protein
●
Eukaryotes
have
a
true
nucleus
w
multiple
sets
of
chromosomes
○
Have
haploid
and
diploid
stages
in
life
cycle
■
Sperm
and
eggs
are
haploid,
combined
they
are
diploid
■
In
diploid
stage,
genome
has
2
copies
(a
homologous
pair)
of
each
gene
○
Some
genomes
(particularly
plants)
have
more
than
2
copies
of
each
chromosome
–
called
polyploidy
●
Plants
and
animals
also
have
genetic
material
in
their
mitochondria
,
specialized
organelles
○
Plants
also
have
genes
in
their
chloroplasts
○
Organelle
genes
produce
proteins
that
perform
important
tasks
●
Cytoplasmic
Inheritance:
refers
to
random
distribution
of
mitochondria/chloroplasts
among
daughter
cells
○
Organelles
are
transmitted
in
cytoplasm
during
cell
division
●
Mitosis:
complete
set
of
chromosomes
transmitted
○
Produces
genetically
identical
daughter
cells
●
Meiosis:
process
in
sexual
reproduction,
produces
sex
cells
(
gametes
)
●
Alleles:
alternative
forms
of
a
gene
that
alter
the
phenotype
●
Genome:
complete
set
of
DNA
sequences ○
Genes,
regions
controlling
those
genes
●
LUCA:
last
universal
common
ancestor
○
All
three
domains
(
eukarya,
bacteria,
archaea
)
evolved
from
LUCA
●
Foundations
of
modern
bio:
○
All
life
on
earth
shares
common
ancestor
(LUCA)
○
DNA
is
hereditary
material
in
all
organisms
●
All
3
domains
share
general
mechanism
of
DNA
replication
and
gene
expression
○
All
organisms
use
transcription
and
translation
■
Transcription:
one
strand
of
DNA
synthesizes
one
strand
of
RNA
■
Translation
:
RNA
codes
for
protein
production
at
the
ribosomes
●
3
branches
of
modern
genetics:
○
Transmission
(Mendelian)
:
transmission
of
traits
in
successive
generations
○
Evolutionary
:
origins
of
and
genetic
relationships
b/n
organisms;
evolution
of
genes/genomes
○
Molecular
:
inheritance
and
variation
in
DNA,
RNA,
proteins,
and
genomes
1.2
Structure
of
DNA
Suggests
a
Mechanism
for
Replication
●
Chargaff’s
Rule:
percent
of
adenine
and
thymine
are
approx.
equal,
and
percent
of
cytosine
and
guanine
are
approx.
equal
○
Helped
form
hypothesis
that
DNA
nucleotides
are
arranged
in
complementary
base
pairs
●
Each
strand
in
the
helix
is
made
of
DNA
nucleotides
w/
3
principle
pieces:
5-carbon
deoxyribose
sugar,
a
phosphate,
and
one
of
4
nitrogen-containing
nucleotide
bases
(A,
C,
T,
or
G)
○
Nucleotides
are
linked
by
a
covalent
phosphodiester
bond
b/n
the
5’
phosphate
group
of
one
nucleotide
and
the
3’
hydroxyl
group
of
the
adjacent
nucleotide
■
This
bond
→
alternating
deoxyribose
sugars/phosphate
groups
on
the
strand
→
sugar-phosphate
backbone
●
Nucleotide
bases
are
hydrophobic
●
Hydrogen
bonds
form
between
the
base
pairs
to
join
two
DNA
strands
into
a
double
helix
○
Two
hydrogen
bonds
for
A–T,
three
for
C–G
●
Each
DNA
strand
has
a
5’
and
a
3’
end
to
establish
strand
polarity
○
Complementary
strands
of
DNA
are
antiparallel
,
so
the
3’
end
of
one
strand
is
matched
with
the
5’
end
of
the
other
●
Semiconservative
Replication:
usual
DNA
replication
mechanism,
the
two
complimentary
helix
strands
separate
and
each
strand
acts
as
a
template
for
a
new
complimentary
strand
○
Each
new
helix
has
a
parental
strand
and
a
new
daughter
strand
●
DNA
only
replicates
in
the
5’-to-
3’
direction 1.3
DNA
Transcription
and
Messenger
RNA
Translation
Express
Genes
●
Central
Dogma
of
Biology:
statement
describing
flow
of
hereditary
info
and
other
central
aspects
of
DNA
and
inheritance
○
Modern
bio
has
clear
understanding
of
the
central
dogma
○
●
Multiple
types
of
RNA
○
Ribosomal
RNA
(rRNA)
:
NOT
translated,
forms
part
of
the
ribosomes
○
Transfer
RNA
(tRNA)
:
NOT
translated,
carries
amino
acids
(building
blocks
of
proteins)
to
the
ribosomes
○
Messenger
RNA
(mRNA)
:
translated
to
make
proteins
●
Reverse
Transcription:
form
of
information
flow
where
an
enzyme
synthesizes
DNA
from
an
RNA
template
that
comes
from
RNA-containing
viruses
Transcription
●
Transcription
:
process
by
which
DNA
info
is
converted
into
an
RNA
sequence
●
Template
Strand:
strand
of
DNA
that
synthesizes
the
transcript
○
RNA
polymerase
pairs
template-strand
nucleotides
w/
their
pair
RNA
nucleotides
●
RNA
uses
uracil
(U)
instead
of
thymine,
which
still
pairs
with
adenine
●
To
begin
transcription,
RNA
polymerase
and
other
necessary
proteins
locate
a
gene,
access
template
strand
by
interacting
with
DNA
sequences
that
initiate
transcription
○
RNA
polymerase
also
ends
transcription
and
releases
transcript
at
the
end
●
Promoters:
most
common
DNA
sequence
controlling
transcription
○
Recognised
by
RNA
polymerase
which
directs
them
to
nearby
gene
○
Not
transcribed
by
RNA
polymerase
●
Eukaryotic
genes
divided
into
exons
which
have
all
the
coding
information
for
translation,
and
introns
which
intervene
between
exons
and
are
removed
before
translation
Translation
●
Translation
:
conversion
of
genetic
info
in
mRNA
into
amino
acid
sequences
●
Amino
acids
joined
together
by
covalent
peptide
bond
,
and
they
string
together
to
form
polypeptides
○
Folded
up
polypeptides
→
proteins
(one
or
more
polypeptides
combined)
●
Translation
occurs
in
the
ribosomes
●
Codon:
set
of
3
consecutive
nucleotides
in
mRNA
which
specify
the
amino
acid
at
each
position
in
the
polypeptide
●
To
begin,
mRNA
attaches
to
ribosome
in
a
way
that
puts
the
start
codon
in
the
right
location
