genetic engineering biology ch.15. selective breeding selective breeding allows only those organisms...
TRANSCRIPT
Genetic Engineering
Biology
Ch.15
Selective Breeding
• Selective breeding allows only those organisms with desired characteristics to produce the next generation.
• Nearly all domestic animals and most crop plants have been produced by selective breeding.
Copyright Pearson Prentice Hall
Selective Breeding
• Humans use selective breeding to pass desired traits on to the next generation of organisms.
Copyright Pearson Prentice Hall
htt
p://
ww
w.w
isd
om
pa
ne
lpro
.com
/vie
w/b
in/im
age
s/d
og_
his
tory
_tr
ee.
jpg
Selective Breeding
• Hybridization – the crossing of dissimilar individuals to bring
together the best of both organisms. – Hybrids, the individuals produced by such
crosses, are often hardier than either of the parents.
Copyright Pearson Prentice Hall
Selective Breeding
• Inbreeding – the continued breeding
of individuals with similar characteristics.
– Inbreeding helps to ensure that the characteristics that make each breed unique will be preserved.
– Serious genetic problems can result from excessive inbreeding.
Copyright Pearson Prentice Hall
http://www.geneticstimes.com/Images/German_shepherd.JPG
Increasing Variation
• Breeders increase the genetic variation in a population by inducing mutations.
• Mutations occur spontaneously, but breeders can increase the mutation rate by using radiation and chemicals.
• Breeders can often produce a few mutants with desirable characteristics that are not found in the original population.
Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall
Increasing Variation
• Producing New Kinds of Bacteria– Introducing mutations has allowed scientists
to develop hundreds of useful bacterial strains, including bacteria that can clean up oil spills.
Copyright Pearson Prentice Hall
Increasing Variation
• Producing New Kinds of Plants– Mutations in some plant cells produce cells
that have double or triple the normal number of chromosomes.
– This condition, known as polyploidy, produces new species of plants that are often larger and stronger than their diploid relatives.
– Polyploidy in animals is usually fatal.
The Tools of Molecular Biology
• Scientists use their knowledge of the structure of DNA and its chemical properties to study and change DNA molecules.
Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall
The Tools of Molecular Biology
• Scientists use different techniques to:– extract DNA from cells– cut DNA into smaller pieces– identify the sequence of bases in a DNA
molecule– make unlimited copies of DNA
Copyright Pearson Prentice Hall
The Tools of Molecular Biology
• In genetic engineering, biologists make changes in the DNA code of a living organism.
Copyright Pearson Prentice Hall
The Tools of Molecular Biology
• DNA Extraction– DNA can be extracted from most cells by a
simple chemical procedure.– The cells are opened and the DNA is
separated from the other cell parts.
Copyright Pearson Prentice Hall
The Tools of Molecular Biology
• Cutting DNA – Most DNA molecules are too large to be
analyzed, so biologists cut them into smaller fragments using restriction enzymes.
• Enzymes found in bacteria used to destroy phage DNA
The Tools of Molecular Biology
• Each restriction enzyme cuts DNA at a specific sequence of nucleotides.
The Tools of Molecular Biology• Separating DNA
– In gel electrophoresis, DNA fragments are placed at one end of a porous gel, and an electric voltage is applied to the gel.
– When the power is turned on, the negatively-charged DNA molecules move toward the positive end of the gel.
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.
The Tools of Molecular Biology
• DNA Fingerprinting– A method of
developing a person’s DNA “profile,” similar to a fingerprint.
– Pioneered in England in 1984 by Dr. Alec Jeffreys
Dr. Alec Jeffreys
How does it work?
• 99.9% of your DNA is the same as everyone else’s.
• The 0.1% that differs are a combination of:– Gene differences (Differences in the genes
themselves)– Differences in “polymorphic regions” between
the genes on the DNA.
How does it work?
• Certain points between the genes on the DNA have repeating base sequences.– For example:
ATTACGCGCGCGCGCGCGCTAGC– These are called variable number tandem
repeats (VNTRs for short)
How does it work?
• Everyone has VNTRs at the same place in their DNA, but they are different lengths for different people.– For example:
Person 1: ATTACGCGCGCGCGCGCGTAGC(7 repeats)
Person 2: ATTACGCGCGCGCGTAGC(5 repeats)
Using the DNA Sequence
• These enzymes also make it possible to take a gene from one organism and attach it to the DNA of another organism.
• Such DNA molecules are sometimes called recombinant DNA.
Copyright Pearson Prentice Hall
BIO
LO
GY
: CO
NC
EP
TS
AN
D C
ON
NE
CT
ION
S 4
th
Edi
tion
, b
y C
am
pb
ell,
Re
ece
, M
itch
ell,
an
d T
aylo
r,
©2
003
.
Copyright Pearson Prentice Hall
Using the DNA Sequence
• Making Copies – Polymerase chain reaction (PCR) is a
technique that allows biologists to make copies of genes.
– A biologist adds short pieces of DNA that are complementary to portions of the sequence.
Using the DNA Sequence
• DNA is heated to separate its two strands, then cooled to allow the primers to bind to single-stranded DNA.
• DNA polymerase starts making copies of the region between the primers.
Copyright Pearson Prentice Hall
Genomic DNA
Targetsequence
5
3
3
5
5
3
3
5
Primers
Denaturation:Heat brieflyto separate DNAstrands
Annealing:Cool to allowprimers to formhydrogen bondswith ends oftarget sequence
Extension:DNA polymeraseadds nucleotides tothe 3 end of eachprimer
Cycle 1yields
2molecules
Newnucleo-
tides
Cycle 2yields
4molecules
Cycle 3yields 8
molecules;2 molecules
(in white boxes)match target
sequence
Genomic DNA
Targetsequence
5
3
3
5
5
3
3
5
Primers
Denaturation:Heat brieflyto separate DNAstrands
Annealing:Cool to allowprimers to formhydrogen bondswith ends oftarget sequence
Extension:DNA polymeraseadds nucleotides tothe 3 end of eachprimer
Cycle 1yields
2molecules
Newnucleo-
tides
Cycle 2yields
4molecules
Cycle 3yields 8
molecules;2 molecules
(in white boxes)match target
sequence
Transforming Bacteria
• During transformation, a cell takes in DNA from outside the cell. The external DNA becomes a component of the cell's DNA.
Copyright Pearson Prentice Hall htt
p://
bio
log
y20
0.g
su.e
du/h
oug
hto
n/4
56
4%
20
%27
04
/fig
ure
s/le
ctu
re%
20
3/
tra
nsfo
rma
tion.
jpg
Transforming Bacteria
• Foreign DNA is first joined to a small, circular DNA molecule known as a plasmid.
• Plasmids are found naturally in some bacteria and have been very useful for DNA transfer.
Copyright Pearson Prentice Hall
Plasmids
• Short, circular DNA molecules outside the chromosome
• Carry genes that are beneficial but not essential
• Replicate independently of chromosome
en.wikipedia.org/?title=Plasmid
Copyright Pearson Prentice Hall
Transforming Bacteria
• The plasmid has a genetic marker—a gene that makes it possible to distinguish bacteria that carry the plasmid (and the foreign DNA) from those that don't.
Transforming Bacteria
How do you know which cells have been transformed?
Copyright Pearson Prentice Hall
Transforming Plant Cells
• How can you tell if a transformation experiment has been successful?
• If transformation is successful, the recombinant DNA is integrated into one of the chromosomes of the cell.
Transforming Plant Cells
• In nature, a bacterium exists that produces tumors in plant cells.
• Researchers can inactivate the tumor-producing gene found in this bacterium and insert a piece of foreign DNA into the plasmid.
• The recombinant plasmid can then be used to infect plant cells.
Copyright Pearson Prentice Hall
Transforming Plant Cells
• When their cell walls are removed, plant cells in culture will sometimes take up DNA on their own.
• DNA can also be injected directly into some cells.
• Cells transformed by either procedure can be cultured to produce adult plants.
Copyright Pearson Prentice Hall
Transforming Animal Cells
• Many egg cells are large enough that DNA can be directly injected into the nucleus.
• Enzymes may help to insert the foreign DNA into the chromosomes of the injected cell.
• DNA molecules used for transformation of animal and plant cells contain marker genes.
http://www.rikenresearch.riken.jp/images/figures/hi_3609.jpg
Transforming Animal Cells• Gene Therapy
– DNA molecules can be constructed with two ends that will sometimes recombine with specific sequences in the host chromosome.
– The host gene normally found between those two sequences may be lost or replaced with a new gene.
Copyright Pearson Prentice Hall
http://library.thinkquest.org/28000/media/genetherapy/l_gene.therapy-ms.gif
Applications of Genetic Engineering
Transgenic Organisms
• An organism described as transgenic, contains genes from other species.
Copyright Pearson Prentice Hall
htt
p://
h
ttp:
//w
ww
.bio
.mia
mi.e
du/~
cma
llery
/150
/ha
ndo
uts
/c17
x5tr
an
sgen
ic-t
oba
cco
.jpg
http://www.bio.miami.edu/~cmallery/150/handouts/D.zebra.htm
Transgenic Organisms
• Genetic engineering has spurred the growth of biotechnology.– Transgenic animals and plants– The Human Genome Project– The production of vaccines, cancer drugs, and
pesticides– Engineered bacteria that can clean up toxic wastes– Cloning
• Organ replacement
Copyright Pearson Prentice Hall
Transgenic Organisms
• Transgenic bacteria produce important substances useful for health and industry. Transgenic bacteria have been used to produce:– insulin– growth hormone– clotting factor
Copyright Pearson Prentice Hall
BIO
LO
GY
: CO
NC
EP
TS
AN
D C
ON
NE
CT
ION
S 4
th E
diti
on,
by
Ca
mp
be
ll, R
ee
ce,
Mitc
he
ll, a
nd
Tay
lor,
©2
00
3.
Transgenic Organisms
• Transgenic animals have been used to study genes and to improve the food supply.
• Mice have been produced with human genes that make their immune systems act similarly to those of humans. This allows scientists to study the effects of diseases on the human immune system.
Copyright Pearson Prentice Hall
htt
p://
ww
w.n
cbi.n
lm.n
ih.g
ov/b
oo
ksh
elf/
br.f
cgi?
bo
ok=
cme
d&
part
=A
953
8
Transgenic Animals
• Nils Lonberg, director at Medarex, bred two genetically modified mice, creating a mouse with a humanized immune system.
• In response to disease-causing agents, these mice make human antibodies in their cells, some of which might be developed into drugs.
http://images.businessweek.com/ss/06/01/critters/source/4.htm
Transgenic Organisms
• Researchers are trying to produce transgenic chickens that will be resistant to the bacterial infections that can cause food poisoning.
Copyright Pearson Prentice Hall http://www.cals.ncsu.edu/agcomm/magazine/spring03/images/transgenic1.jpg
Copyright Pearson Prentice Hall
Transgenic Organisms
• Transgenic plants are now an important part of our food supply.
• Many of these plants contain a gene that produces a natural insecticide, so plants don’t have to be sprayed with pesticides.
Transgenic Plants
• Bt Corn– Engineering resistant
corn. Following the insertion of a gene from the bacteria Bacillus thuringiensis, corn becomes resistant to corn borer infection. This allows farmers to use fewer insecticides
http://www.scq.ubc.ca/bt-corn-is-it-worth-the-risk/
htt
p://
ww
w.b
io.d
avi
dso
n.e
du/p
eo
ple
/ka
ber
nd
/se
min
ar/
20
04
/GM
eve
nts
/LH
/cor
ne
ar.
jpg
• “Golden rice” has been genetically modified to contain beta-carotene
– This rice could help prevent vitamin A deficiency
Figure 12.18B
Cloning
• A clone is a member of a population of genetically identical cells produced from a single cell.
• In 1997, Ian Wilmut cloned a sheep called Dolly.
Copyright Pearson Prentice Hall
Dolly and Bonnie
Cloning
Cloning
• Researchers hope cloning will enable them to make copies of transgenic animals and help save endangered species.
Copyright Pearson Prentice Hall
htt
p://
reso
urc
es.
ed
b.g
ov.h
k/b
iolo
gy/
eng
lish
/ima
ges
/ge
net
ics/
pan
da
.gif
Copyright Pearson Prentice Hall
Cloning
• Studies suggest that cloned animals may suffer from a number of genetic defects and health problems.– Abnormal gene expression– “old” DNA
• Our new genetic knowledge will affect our lives in many ways
• The deciphering of the human genome, in particular, raises profound ethical issues– Many scientists have
counseled that we must use the information wisely
DNA technology raises important ethical questions
Figure 12.21A-C
• Genetic engineering involves some risks– Possible ecological damage
from pollen transfer between GM and wild crops
– Pollen from a transgenic variety of corn that contains a pesticide may stunt or kill monarch caterpillars
Could transgenics harm human health or the environment?
Figure 12.20A, B