E. coli

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14 Δεκ 2012 (πριν από 4 χρόνια και 9 μήνες)

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Chapter 13

Genetic Technology

Selective Breeding


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


Why?


Examples?


Milk Cows


1947
-

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


1997
-

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


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

Inbreeding


Mating between closely
related individuals


Why?


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”

Hybrids


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
wild?


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
technology.


Connecting, or recombining,
fragment of DNA from different
sources

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

Vectors


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
cell


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

Insertion Into a
Vector


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
DNA


Up to 500 copies per
cell


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
specificity

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
future

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
hemophilia


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


This protein can then be given to hemophilia
patients

Recombinant DNA in
Agriculture


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.