E. coli


14 Δεκ 2012 (πριν από 5 χρόνια και 7 μήνες)

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Chapter 13

Genetic Technology

Selective Breeding

For a long time, humans have selected the
best plants and animals to



Milk Cows


produced 4,997 lbs... of milk/year


produced 16,915 lbs.... of milk/year

Increasing the frequency of desired alleles
in a population is the essence of genetic


Mating between closely
related individuals


Done to make sure that
breeds consistently exhibit a
trait and to eliminate
undesired trait

Creates purebred lines

Can be bad also

Can bring out harmful,
recessive alleles in a “family”


It can be beneficial to
create hybrids

For example, disease
resistant plants crossed
with plants that produce
bigger fruit

Offspring get both qualities

Hybrids produced by
crossing two purebred
plants are often larger and
stronger than their parents

Test Crosses

A test cross is a cross of an
individual of unknown
genotype with an
individual of known
genotype (usually
homozygous recessive)

How will this work?

Results when heterozygous
x homozygous?

Results when homozygous
x homozygous?

When is this practical?

Section 1 Review

A test cross made with a cat that may be heterozygous for
a recessive trait produces ten kittens, none of which has the
trait. What is the presumed genotype of the cat? Explain.

Suppose you want to produce a plant that has red flowers
and speckled leaves. You have two offspring, each having
one of the desired traits. How would you proceed?

Why is inbreeding rarely a problem among animals in the

Hybrid corn is produced that is resistant to bacterial
infection and is highly productive. What might have been
the phenotypes of its two parents?

How is selective breeding done?

What effect might selective breeding of plants and animals
have on the size of Earth’s human population? Why?

Genetic Engineering

Selective breeding may take a while to
produce a purebred “line”

Genetic engineering is a faster and more
reliable method for increasing the
frequency of an allele in a population

This involves cutting

or cleaving

DNA from one organism into small
fragments and inserting the fragments
into a host organism of the same or a
different species

Also called recombinant DNA

Connecting, or recombining,
fragment of DNA from different

Transgenic Organisms

Plants and animals that contain functional recombinant DNA from
an organism of a different genus

Ex: they grow a tobacco plant that glows from a gene in a firefly

3 steps:

Isolate the foreign DNA fragment to be inserted

Attach the DNA fragment to the carrier

Transfer the DNA into the host organism

Restriction Enzymes

Bacterial proteins that have the ability to cut
both strands of the DNA molecule at a
specific nucleotide sequence

Some enzymes cut straight across

Called blunt ends

Restriction Enzymes

Many enzyme cut in palindromes

Ex: a protein only cuts at AATT, it will cut the two
fragments at different points

not across from each
other (called sticky ends)

Called sticky ends because they want to bond with things
due to their “open” end

These sticky ends are
beneficial, because if the
same enzyme is used in
both organisms, they will
have identical ends and
will bond with each other


DNA fragments don’t just attach themselves to another
fragment, they need a carrier

A vector is the means by which DNA from another
species can be carried into the host cell

Vectors may be biological or mechanical

Biological vectors include viruses and plasmids

A plasmid is a small ring of DNA found in a bacterial

Mechanical vectors include micropipettes
and a little metal bullet coated with DNA
shot with a gene gun into a cell

Insertion Into a

If the plasmid and the
DNA fragment were
both cleaved with the
same enzyme, they
will stick together
because they have
“sticky ends”

A second enzyme
helps this process

Gene Cloning

Once the fragment is in the
plasmid, the bacterial
makes many copies of the

Up to 500 copies per

Clones are genetically
identical copies

Each copied recombinant
DNA molecule is a clone

If the plasmid is placed
into a plant or animal cell,
the cell reproduces that
DNA also and makes those
proteins coded for

Cloning Animals

Dolly was the first animal cloned in 1997

Since then, goats, mice, cattle, pigs, etc.
have been cloned

Take DNA out of embryonic stem cells or
zygote and insert new DNA

Recombinant DNA in Industry

E. coli

has been modified to produce an
indigo dye to color blue jeans

Recombinant DNA has been used to help
production of cheese, laundry detergent,
paper production, sewage treatment

Increase enzyme activity, stability and

Recombinant DNA in Medicine

Production of Human
Growth Hormone to treat
pituitary dwarfism

Insulin Production by
bacterial plasmids

Antibodies, hormones,
vaccines, enzymes, and
hopefully more in the

Transgenic Animals

Mice reproduce quickly and have
chromosomes that are similar to humans’

The genome is known better

The roundworm
Caenorhabditis elegans

and the fruit fly,
Drosophila melanogaster

are also well understood

Used in transgenic studies

Transgenic Animals

A transgenic sheep was produced that
contained the corrected human gene for

This human gene inserted into the sheep
produces the clotting protein in the sheep’s

This protein can then be given to hemophilia

Recombinant DNA in

Crops that stay fresh longer and are more
resistant to disease

Plants resistant to herbicide so weeds can be
killed easier

Higher product yields or higher in vitamins

Peanuts and soybeans that don’t cause
allergic reactions

Section 2 Review

How are transgenic organisms different from
natural organisms of the same species?

How are sticky ends important in making
recombinant DNA?

How does gel electrophoresis separate fragments
of DNA?

What is a restriction enzyme?

What is PCR?

Explain two ways in which recombinant bacteria
are used for human applications.

Many scientists consider engineering to be simply
an efficient method of selective breeding. Explain.