Transcript CHAPTER 13 GENETIC ENGINEERING

13-1 Changing the Living World
A. Selective Breeding
- allowing only animals with the desired
characteristics to produce the next generation
- used to pass desired traits onto the next generation
- horses, farm animals, cats, dogs and most crop
plants have been produced this way
Examples:
1. hybridization
- crossing unlike individuals to bring together the best
of both organisms
- produces hybrids which are hardier than either of the
parents
- used first by Luther Burbank who produced new lines
of plants in order to increase food production
2. inbreeding
- the continued breeding of individuals with similar
characteristics in order to maintain the desired
characteristics of a line of organisms
- seen in many dog breeds; ensures that the
characteristic that make each breed unique will be
preserved
- risky because inbreeding of genetically similar
animals can lead to genetic defects including blindness and
joint deformities
Inbred Cat species
B. Increasing Variation
- breeders can increase genetic variation in a
population by bringing about mutations, which are the
source of genetic variability
- mutations are inheritable changes in DNA that occur
spontaneously
- breeders increase mutations by using radiation and
chemicals
Examples:
1. Producing new kinds of bacteria
- bacterial size enables large numbers of organisms to
be treated with radiation or chemicals at the same time thus
increasing the chance of producing a successful mutant
- this technique has produced useful bacterial strains
such as bacteria that digest oil, and are used in the cleanup
of oil spills
2. Producing new kinds of plants
- drugs have been used to prevent chromosomal
separation during meiosis resulting in polyploidy (double or
triple to the number of chromosomes)
- polyploidy is fatal in animals but in plants producers
new species that are large and stronger than normal
Ex. bananas and citrus fruits
13-2 Manipulating DNA
- scientists can use their knowledge of DNA structure
and its chemical properties to study and change DNA
molecules
- different techniques are used to remove DNA from
cells, cut it into small pieces, identify the sequence of bases
in the DNA piece, and make unlimited copies
A. The tools of Molecular Biology
In genetic engineering, changes are made in the DNA code
1. DNA extraction
- the cells are opened chemically and the DNA is
separated from other parts of the cell
DNA Extraction
2. Cutting DNA
- restriction enzymes are used to cut the large strands
of DNA into smaller fragments
3. Separating DNA
- DNA fragments are separated using gel
electrophoresis
- Identifies genomes of different organisms
- Can locate one gene from millions of others
Gel electrophoresis
B. Using the DNA Sequence
1. Reading the sequence
- an automated process (See Fig 13-7)
- allows researchers to study specific genes
2. Cutting and Pasting
- method used to change DNA sequences
- synthetic sequences made from a DNA synthesizer
can be added to natural ones or a gene from one organism
can be attached to the DNA of another organism
- these DNA molecules are called “recombinant DNA”
because they are formed by combining DNA from different
sources
3. Making copies
- the technique called a polymerase chain reaction
(PCR) is used to make multiple copies of a particular gene
(See Fig 13-8)
13-3 Cell Transformation
During transformation, a cell takes in DNA from outside the cell
and this outside DNA becomes a part of the cell’s DNA
A. Transforming bacteria (See Fig 13-9)
- foreign DNA is joined to a small, circular DNA molecule
called a plasmid found in many bacteria
- plasmids are useful for DNA transfer
- plasmids containing foreign DNA that find their way into
bacterial cells are guaranteed to be replicated
- also, plasmids contain a genetic marker so it is easy to
identify bacteria that carry the plasmid with the foreign bacteria
from those that don’t
B. Transforming plant cells (Fig 13-10)
- in nature, a bacterium inserts a small DNA plasmid
that produces tumors into a plant’s cells
- researchers can inactivate the tumor-producing gene
and insert foreign DNA into the plasmid
- the recombinant plasmid can be used to infect plant
cells
C. Transforming animal cells (See Fig 13-11)
- animal cells are transformed in some of the same
ways as plant cells
- the recombinant DNA can be used to replace a gene
in an animal’s genome
- a mutated gene that causes a disorder can be replaced
by a normal gene
13-4
Applications of Genetic
Engineering
- this technology makes it possible to transfer DNA
sequences, including whole genes, from on organism to
another
A. Transgenic organisms
- organisms that contain genes from other organisms
- these transformed cells can be used to grow new
organisms
1. transgenic microorganisms
- produce important substances useful for health and
industry
- transformed bacteria now produce proteins such as
insulin, growth hormone, and clotting factor cheaply and in
large quantities
- in the future, anticancer substances could be
produced as well as the raw materials for plastics and
synthetic fibers
2. transgenic animals
- used to study genes and improve the food supply
- mice are used to study the effects of disease on the
human immune system
- transgenic livestock have extra copies of genes that
produce human growth hormone and they grow faster and
produce meat with less fat
- transgenic chickens are being studied that will be
resistant to bacterial infections that cause food poisoning
- in the future, animals may provide us with large
amounts of our own proteins
Transgenic livestock (cow)
Transgenic chicken
3. transgenic plants
- an important part of our food supply
- most of soybean and corn grown in the US is transgenic
or genetically modified
- many plants contain genes that produce a natural
insecticide
- other plants have genes that resist weed-killing chemicals,
so farmers can control weeds while not harming the crop
- they may soon produce antibodies that can be used to
fight disease, plastics, and foods resistant to rot and spoilage
- an important new development is a rice plant that adds
Vitamin A to the rice
Transgenic corn
B. Cloning
Clone
- a member of a population of genetically identical cells
produced from a single cell
- bacterial cells are easy to grow but this is not true of
multicellular organisms like animals
- See Fig 13-15; Steps in cloning the first mammal by Ian
Wilmut (1997)
- Cloned cows, pigs, mice, and other mammals have been
produced
- Cloning may be important for use in medical and scientific
research and in helping to save endangered species
- Serious ethical issues are raised particularly involving possible
cloning of a human