Book Reference (Chapter 13 Genetic Engineering)

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Unit 10 Biotechnology NOTES

Book Reference (Chapter 13 Genetic Engineering)


Changing the Living World

Selective Breeding

What is the Purpose of 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.



Humans use selective breeding to pass desired traits on to the next
generation o
f organisms.

Hybridization
-

is 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.


Inbreeding

is 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.



Increasing Variation

Why might breeders try to in
duce mutations?

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
desira
ble characteristics

that are
not found in the original population.


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.


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.






Quiz yourself
-

1.


The usual function of selective breeding is to produce organisms that

a.


are better suited to their natural environment.

b.



have characteristics useful to humans.


c.


can compete with othe
r members of the species that are not selected.


d.



are genetically identical.


2.


Crossing a plant that has good disease
-
resistance with a plant that has a
good food
-
producing capacity is an example of

a.


inbreeding.


b.

hybridization.


c.

polyploidy.


d.

crossing

over.


3.

New species of plants that are larger and stronger are a result of

a.

monoploidy.


b.

diploidy.


c.

polyploidy.


d.

triploidy.



4.

The function of inbreeding is to produce organisms that


a.


are more genetically diverse.


b.

are much healthier.


c.

are

genetically similar.


d.

will not have mutations


5.


Increasing variation by inducing mutations is particularly useful with

a.


animals.


b.

bacteria.


c.

plants.


d.

fungi.

Manipulating DNA

The Tools of Molecular Biology

How do scientists make changes to DNA?

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

In
genetic engineering
, biologists make changes in the DNA code of a living
organism.


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.


Cutting DNA


Most DNA molecules are too large to be analyzed, so biologists cut them into
smaller frag
ments using
restriction enzymes
.


Which type of molecule is an enzyme?

Proteins




Each
restriction enzyme

cuts DNA

at a specific sequence of nucleotides.





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.


Recognition Sequence

Gel Electrophoresis

1

2

3

Steps for Gel Electrophoresis
-

1
-

First,
restriction enzymes cut DNA

into fragments.

The DNA fragments are poured
into wells on a gel.

2
-

An electric voltage is applied to the gel.

The smaller the DNA fragment, the
faster and farther

it will move across
the gel.

3
-

DNA molecules are
negatively charged
. An electric voltage is applied to

the

gel. The smaller the fragment, the further it moves.

Making Copies


Polymerase chain reaction
(PCR)

is a technique that allows biologists to
make
copies of genes.


Small amounts of DNA can be multiplied making it easier to analyze.




Quiz yourself
-

1.


Restriction enzymes are used to


a.

extract DNA.


b.

cut DNA.


c.

separate DNA.


d.

replicate DNA.



2.

During gel electrophoresis, the smaller the DNA fragment is, the

a.
more slowly it moves.


b.
heavier it is.


c
. more quickly it moves.


d.
darker it stains.


3.

A particular restriction enzyme is used to



a.
cut up DNA in random locations.



b. cut DNA at a specific nucleotide sequence.



c.
extract DNA from cells.



d.
separate negatively charged DNA molecules.



4.
During gel
electrophoresis, DNA fragments become separated because


a.
multiple copies of DNA are made.


b.
recombinant DNA is formed.


c.
DNA molecules are negatively charged.


d
. smaller DNA molecules move faster than larger fragments.



Cell Transformation

Tra
nsforming Bacteria

What happens during cell transformation?

During transformation, a cell takes in DNA from outside the cell. The
external DNA becomes a component of the cell's DNA.


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.


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


During
transformation
, a cell incorporates DNA from outside the cell into its
own DNA. One way to use bacteria to produce human growth hormone is to
insert a human gene into bacterial DNA. The new combination of genes is
then return
ed to a bacterial cell. The bacterial cell containing the gene
replicates over and over.

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
.

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.


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.

Transforming Plant Cells


If the transformation is successful, the DNA will be integrated into one of
the cell’s chromosomes
.

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.

DNA molecules can be constructed with two ends that will sometimes
recombine
with sp
ecific sequences in the host chromosome.

The
host gene

normally found between those two sequences may be
lost or
replaced with a new gene.

Transforming Animal Cells


Recombinant DNA can replace a gene in an animal’s genome. The ends of the
recombinant DNA

recombine with sequences in the host cell DNA. When the
recombinant DNA is inserted into the target location, the host cell’s original
gene is lost or knocked out of its place.





Quiz Yourself

1.


Plasmids can be used to transform


a.


bacteria only.


b.

plant

cells only.


c.

plant, animal, and bacterial cells.


d.

animal cells only.


2.

An unknowing pioneer in the concept of cell transformation was


a.

Luther Burbank.


b.

Frederick Griffith.


c.

Oswald Avery.


d.

James Watson.

3.


One reason plasmids are useful in cell transformation

is that they

a.


are found in all types of cells.


b.

prevent gene replication.


c.

counteract the presence of foreign DNA.


d.

have genetic markers indicating their presence.

4.

A common method of determining whether bacteria have taken in a
recombinant plasmid is to

a.

introduce them into plant cells.


b.

introduce them into animal cells.


c.

treat them with an antibiotic.


d.

mix them with other bacteria that do not have the plasmid.


5.

Successful transformation of an animal or a plant cell involves


a.
the integration of r
ecombinant DNA into the cell’s chromosome.


b.
changing the cell’s chromosomes into plasmids.


c.
treating the cell with antibiotics.


d.
destroying the cell wall in advance.


Transgenic

Organisms

An organism described as transgenic, contains genes from
other species.

How are transgenic organisms useful to human beings?

Genetic engineering has spurred the growth of biotechnology.

Transgenic Microorganisms

Transgenic
bacteria

produce important substances useful for health and industry.
Transgenic bacteria have been used to produce:



insulin



growth hormone



clotting factor


Transgenic Animals

Transgenic animals have been used to
study genes and to improve the food supply.


Mice h
ave 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.

Researchers are trying to produce transgenic chickens that will be resis
tant to
the bacterial infections that can cause food poisoning.


Transgenic
Plants


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.



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.


Researchers hope cloning will enable them to make copies of
transgenic

animals
and help save
endangered species
.

Studies suggest that
cloned animals

may suffer from a number of
genetic defects
and health problems.





Quiz Yourself

1.

Insulin
-
dependent diabetes can now be treated with insulin produced
through the use of


a.

trans
genic plants.


b.

transgenic animals.


c.

transgenic microorganisms.


d.

transgenic fungi.


2.

Transgenic tobacco plants that glow in the dark were produced by
transferring the gene for luciferase from a


a.

clone.


b.

bacterium.


c.

firefly.


d.

jellyfish.

3.

The first mammal to b
e cloned was a


a.

sheep.


b.

horse.


c.

dog.


d.

cat.

4.


In producing a cloned animal, an egg cell is taken from a female and its
nucleus is removed. A body cell is taken from a male. The clone from this
experiment will


a.

look just like the female.


b.

be

genetically identical to the male.


c.

have a mixture of characteristics from both animals.


d.

resemble neither the male nor the female

5.

Animals produced by cloning have been shown to

a.

all be perfectly healthy.


b.

suffer from a number of health problems.


c.

live

longer than uncloned animals.


d.

be less intelligent than uncloned animals.