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GENETIC ENGINEERING: CHAPTER 9
CHANGING THE WORLD

Selective Breeding
o Allows only those organisms with desired characteristics to produce the next generation.
o Nearly all domestic animals and most crop plants have been produced by selective breeding.

Hybridization
o Crossing of dissimilar individuals to bring together the best of both organisms.
o Hybrids, the individuals produced by such crosses, are often hardier than either of the parents.

Inbreeding
o Continued breeding of individuals with similar characteristics.
o Helps to ensure that characteristics that make each breed unique will be preserved.
o Serious genetic problems can result from excessive inbreeding.

Increasing Variation
o Accomplished by inducing mutations into a population
o Mutations occur spontaneously, but breeders can increase the mutation rate by using radiation
and chemicals.
o Breeders can often produce a few mutants with desirable characteristics that are not found in
the original population.
o Beneficial?

Introducing mutations has allowed scientists to develop hundreds of useful bacterial
strains, including bacteria that can clean up oil spills.

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.
MANIPULATING DNA

Scientists use different kinds of techniques to:
o extract DNA from cells
o cut DNA into smaller pieces
o identify the sequence of bases in a DNA molecule
o make unlimited copies of DNA

Genetic Engineering:
o biologists make changes in the DNA code of a living organism

DNA Extraction
o The cells are opened and the DNA is separated from the other cell parts
through a simple chemical procedure

Cutting DNA
o Most DNA molecules are too large to be analyzed, so
biologists cut them into smaller fragments using
restriction enzymes
o Each restriction enzyme cuts DNA at a specific sequence
of nucleotides.

Separating DNA
o In gel electrophoresis, DNA fragments are placed at one end of a porous gel, and an electric
voltage is applied to the gel

First, restriction enzymes cut DNA into fragments.

The DNA fragments are poured into wells on a gel.

An electric voltage is applied to the gel.

The smaller the DNA fragment, the faster and farther it will move across the gel.
o “Reading” DNA: Southern Blotting

In genetically modified organisms, Southern blots are used to make certain that the
necessary section of DNA has been inserted into the genome of the organism being
modified

Steps:

DNA is separated from its source and cut with a restriction enzyme

The fragments are put into a gel and sorted by electrophoresis in order of length, the
shortest at the top and the longest at the bottom

A chemical is used to make the fragments visible, and the DNA is moved from the gel on
to a nylon membrane

A radioactive probe is added, which attaches to complementary DNA fragments

The nylon membrane is then covered with an X-ray film which, once developed, reveals
the position of the probe

Making Copies of DNA
o Polymerase chain reaction (PCR) is a technique that allows biologists to make copies of genes.
o Small amounts of DNA can be multiplied making it easier to analyze.
o Made possible by an enzyme found in a bacterium living in hot springs in Yellow Stone
National Park.
CELL TRANSFORMATION

Transforming Bacteria
o During transformation, a cell takes in DNA from outside the cell. The external DNA becomes a
part of the cell's DNA
o Steps:

Foreign DNA is first joined to a small, circular DNA molecule known as a plasmid.

Found naturally in some bacteria

Very useful for DNA transfer.

Contains a genetic marker

Gene that makes it possible to distinguish bacteria that carry the plasmid (and the
foreign DNA) from those that don't.

How can you tell if a transformation has been successful?
o The recombinant DNA is integrated into one of the chromosomes of the cell.

Bacteria:
o A certain bacterium exists that produces tumors in plant cells.
o Researchers inactivate the tumor-producing gene found in this bacterium and insert a piece of
foreign DNA into the plasmid.
o The recombinant plasmid can then be used to infect plant cells.

Plants:
o When their cell walls are removed, plant cells in culture will sometimes take up DNA on their
own.
o DNA can also be injected directly into some cells.
o Cells transformed by either procedure can be cultured to produce adult plants.

Animals:
o Many egg cells are large enough that DNA can be directly injected into the nucleus.
o Enzymes may help to insert the foreign DNA into the chromosomes of the injected cell.
o DNA molecules used for transformation of animal and plant cells contain marker genes.
o DNA molecules can be constructed with two ends that will sometimes recombine with specific
sequences in the host chromosome.
o The host gene normally found between those two sequences may be lost or replaced with a
new gene.
APPLICATIONS OF GENETIC ENGINEERING

Transgenic Organisms
o An organism described as transgenic, contains genes from other species.
o Uses

Microorganisms

Transgenic bacteria produce important substances useful for health and industry.

Inexpensive

Easy to manufacture

Have been used to produce:
o insulin
o growth hormone
o clotting factor

Animals

Have been used to study genes and improve the food supply.

Mice have been produced with human genes that make their immune systems act like
those of humans.

Allows scientists to study the effects of diseases on the human immune system without
having to study them ON humans.

Researchers are trying to produce transgenic chickens that to be resistant to bacterial
infections that cause food poisoning.

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
o A clone is a member of a population of genetically identical cells produced from a single cell.
o In 1997, Ian Wilmut cloned a sheep called Dolly