Vince
Zi
Shan
Zach
Verdi
Fixler
Most of the organisms
that are used in
agriculture
(crops,
livestock) have been
produced by human
beings by selective
breeding, which is
sometimes called
artificial
selection.
Humans have been
doing this for
thousands of years!
For example, the
wild
banana
looks
very different from
the yellow
Chiquita
you might purchase
in the store.
These fruit are
not
sweet
and are filled
with unpleasant
seeds
.
The good
-
tasting
varieties
most of us
take for granted were
produced long ago by
Africans
who crossed
different
varieties
, and
selected the offspring
that were more
pleasant to taste in
every generation.
The results of
these crosses,
called
hybrids,
became the basis
of the modern
fruit.
In the same way,
Native
Americans
selected varieties of a
naturally
-
occurring
plant called
teosinte
that were a little bit
taller and had
more
seeds
.
Over time, this plant,
known as
maize
or
corn, became very tall
and produced a
gigantic cob with many
kernels
.
The same thing is true for most
varieties of livestock and
pets
:
their
populations
look different
from those in nature.
Why?
Because, over time,
humans
have
selected for the
trait
that they
find most useful or attractive. To
do this, they cross individuals with
similar characteristics, a process
known as
inbreeding
.
Woof!
What about
animals?
The same thing is true for most
varieties of livestock and
pets
:
their
populations
look different
from those in nature.
WHY ?
Because, over time,
humans
have
selected for the
trait
that they
find most useful or attractive. To
do this, they cross individuals with
similar characteristics, a process
known as
inbreeding
.
This is not
necessarily in
the animal’s
best interest,
because it can
increase the
chances of
offspring having
genetic
disorders.
For example,
Dalmation
females often
have pups born
deaf
in one ear,
or with
liver
disease.
Genetic
engineering is
really no different! It’s
just another form of
selective breeding, only
in this case humans are
selecting the
genes
directly, instead of the
traits
based on the
genes
.
Grafting
•
Go to computers and see two ways to
clone… Should take no more than 10
minutes!
•
You will be quizzed on what you learn in
the next 10 minutes!
Once scientists learned
that DNA was the
genetic
material, they
developed techniques to
harvest
it from living
cells.
Restriction Enzymes
(R.E.)
•
*used to cut virus DNA, into fragments to
kill the virus(defense mechanism).
•
R.E. are found in bacteria
•
*large variety of restriction enzymes
exist:
http://www.youtube.com/watch?v=8rXizmLjegI
•
Bam HI G/GATCC
•
Hind III A/AGCTT
•
EcoRI
G/AATTC
Scientists do more than
just collect DNA,
however. They
concentrate and
purify
it, then cut the long
strands of DNA into
smaller fragments with
restriction
enzymes
made by bacteria.
There are hundreds of
different
restriction
enzymes known, and
each one cuts the DNA
at a specific
nucleotide
sequence .
.
Restriction enzyme
EcoRI cuts the DNA into
fragments.
DNA sequence
recognition sequence
“sticky end”
For example, the enzyme
EcoRI
cuts the sequence
‘G/AATTC’ between the ‘G’ and the first ‘A’.
This leads to many DNA fragments of different
sizes
.
.
.
•
uses a
power
source,
a tray filled with
buffer
solution and an
agarose
gel
•
involves ‘loading’ a
mixture of DNA fragments
into little cavities in the
gel, called
wells
.
.
•
applies an electric field
to the
negatively
-
charged
DNA fragments, which
move to
positive pole.
•
separates the fragments
over time, since the
smaller
fragments move
faster and
farther
.
.
•
produces a pattern of
lines that can be read
like a
bar
code at the
supermarket:
Click me to see
a Flash animation!
.
.
.
.
DNA plus
restriction
enzyme
mixture
of DNA
fragments
agarose
gel
power
source
longer
fragments
shorter
fragments
Heating destroys
most enzymes,
including the enzyme
that helps DNA
copy itself, DNA
polymerase
.
But in 1969, a
microbiologist named
Thomas Brock discovered
a species of bacteria
living in the hot springs
of Yellowstone National
Park . . .
This bacteria, which
Brock named
Thermus
aquaticus
, thrives at
just below the
boiling
point of water. . .
Researchers use
this enzyme to
make many copies
of the DNA with a
technique called
polymerase chain
reaction
, or PCR.
PCR takes advantage
of the fact that the
double
-
stranded DNA
fragments will
separate
into two
single
-
stranded
fragments when heated.
In PCR, researchers will
heat the DNA along with
the
Taq
enzyme, along
with a vast surplus of all
the different
nucleotides
:
G’s, C’s, A’s and T’s.
The strands
will separate!
(completely)
The mixture is then
allowed to cool, and
as it does the enzyme
will attach the free
nucleotides
to the
exposed strands . .
. . leading to
two
copies
of double
-
stranded DNA!
This process of
heating and cooling
can be repeated
several times, each
time doubling the
number of copies: in
less than 12 hours,
researchers can
manufacture
millions
of copies of a single
strand.
DNA fragment
to be copied
DNA heated to
separate strands
DNA polymerase adds
complentary strands
DNA fragment
to be copied
DNA heated to
separate strands
DNA polymerase adds
complentary strands
PCR
cycle: ____ _____ _____ _____ _____
DNA
copies: ____ _____ _____ _____ _____
1
2
2
4
3
8
4
16
5
32
laser
Once strands are copied,
researchers will label
the DNA by attaching
different
-
colored chemical
dyes to the different
nucleotides
.
O
nce
s
tr
and
s
a
re
cop
i
e
d,
re
sea
r
ch
ers
wi
ll
la
be
l
th
e
D
NA
by
att
ach
in
g
di
ffe
r
ent
-
col
or
ed
ch
e
m
ic
a
l
dy
es
t
o
th
e
d
if
fer
en
t
nu
cle
o
tid
es
.
Si
nce
e
ac
h ba
se
i
s
labe
l
e
d
Wi
th
a
d
iffe
r
ent
co
lo
r,
th
e
o
rder
of
the
G’s
, T’
s
an
d C’
s
ca
n be
r
ead
b
y
a
laser
and
r
ec
ord
ed
b
y
a
co
mpu
ter
.
laser
The success of the Human
Genome
Project is based
on the fact that the entire process is
automated
Gel
electrophoresis
and
DNA
sequencing
can be
used to identify individuals
(
DNA fingerprinting
) or to
develop genetic profiles of
entire
populations
.
A famous photograph from the O.J. Simpson trial: the blood allegedly
found on the famous athlete’s sock was not his!
Gel
electrophoresis
and
DNA
sequencing
can be
used to identify individuals
(
DNA fingerprinting
) or to
develop genetic profiles of
entire
populations
.
Click on the map!
This information can
be used to determine
paternity
, to link
suspects in a
criminal
investigation to a
crime
scene or to
probe an individual’s
medical
history or
ancestry.
In many cases, it is not necessary to have a copy
of all of an individual’s DNA, only a specific
sequence
which is already well
-
described.
In many cases, it is not necessary to have a copy
of all of an individual’s DNA, only a specific
sequence
which is already well
-
described.
Not all parts of the DNA
are
expressed (exons),
and
many parts that are
not
expressed (so
-
called
‘junk’
DNA
, or
introns
) have
sequences that are repeated
over and over.
These regions of DNA accumulate many harmless
mutations
which are different for every individual.
So, when these regions are cut by
restriction
enzymes, they create unique patterns that can be
used to identify an individual.
This technique,
often used in law
enforcement,
is called
RFLP
:
R
estriction
F
ragment
L
ength
P
olymorphism
(pronounced ‘rif
-
lip’)
This technique,
often used in law
enforcement,
is called
RFLP
:
R
estriction
F
ragment
L
ength
P
olymorphism
(pronounced ‘rif
-
lip’)
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