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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, diseaseresistant 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
Labs
• Mini-Lab 13.1
– Page 343
• Modeling Recombinant DNA
– Page 354
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
Polymerase Chain Reaction
• A way to artificially replicate DNA
• DNA is heated and the strands separate
• An enzyme isolated from a heat-loving
bacterium is used to replicate the DNA
when nucleotides are added (in a
thermocycler)
– Makes millions of copies in less than a day
• Why could this be helpful?
Sequencing DNA
• First, PCR is done to make millions of copies
• Separate the strands of DNA
• Place in four different tubes with four different restriction
enzymes that cut at one of the four bases (A,T,C,G)
– A fluorescent tag is also placed at each cut
• The fragments are separated according to size by a process
called gel electrophoresis
– Produces a pattern of
fluorescent bands in
the gel
• Shows the sequence of
DNA
Gel Electrophoresis
• The gel is like firm gelatin
– Molded with small wells at one end
– Has small holes in the gel (not visible)
• DNA has a slight negative charge
• A current is run through the gel and an
added buffer fluid
– DNA will move towards the positive end
• Smaller fragments fit through the holes in
the gel better and move farther
Gel Electrophoresis
gslc
Gel Electrophoresis Lab
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.
The Human Genome
• In 1990, scientists in the U.S.
organized the Human Genome Project
(PGP)
– An international effort to
completely map and sequence the
human genome
• Approximately 20,000 - 25,000 genes
on 46 chromosomes
• In February, 2001, the PGP published
its working draft of the 3 billion base
pairs in most human cells
• Mini-lab, page 350 (as a class)
Linkage Maps
• Crossing over occurs
• Geneticists use the
frequency of
crossing over to map
the relative position
of genes on a
chromosome
– Genes that are further
apart are more likely
to have crossing over
occur
Linkage Mapping
• Suppose there are 4 genes on a chromosome – A, B,
C, D
• Frequencies of recombination as follows:
–
–
–
–
Between A & B: 50% (50 map units)
Between A & D: 10% (10 map units)
Between B & C: 5% (5 map units)
Between C & D: 35% (35 map units)
• These give a relative distance between genes
• A -10 units- D -35units- C -5 units- B (whole thing
is 50 units)
Linkage Mapping
• The problem with this in humans, is that we
have relatively few offspring
• Geneticists mark genes that have specific
sequences
• They can follow these through inheritance
and hopefully see what it does
– If a gene is marked, not passed on and that trait
doesn’t show up, it may help identify the gene
Sequencing the
Human Genome
• Genome is cloned,
cut into segments,
and then run through
gel electrophoresis
• Arrange the
fragments and get a
sequence
• Machines can do
this much faster
Applications of HGP
• Probably the biggest application so far has
been the identification of genetic disorders
• Often done prenatal
– Take cells from
amniotic fluid and
look for deviations
Gene Therapy
• The insertion of normal genes into human
cells to correct genetic disorders
• Have been used for SCID (severe combined
immunodeficiency syndrome), cystic
fibrosis, sickle-cell anemia, hemophilia and
others.
• Scientists are hopeful his will help treat
cancer, heart disease, AIDS and many other
things.
DNA Fingerprinting
• Genes are separated by segments of
noncoding DNA (“junk DNA”)
– These segments produce distinct combinations
of patterns unique to each individual
• What are the uses?
DNA Fingerprinting
• Small DNA sample
obtained
• Clone samples with PCR
• Cut into fragments
• Separated by gel
electrophoresis
• Chances of two identical
matches are infinitesimally
small
Stem Cells
• An undifferentiated cell
– Doesn’t have a specific function yet
• Will eventually become differentiated
– It will get a specific function and then can only
do certain thins
• GSLC site
Other Uses of DNA Technology
•
•
•
•
•
Look at mummies to understand them
Looked at Abraham Lincoln’s hair
Look at fossils and compare extinct species
They now seem unlimited.
Is that a good thing?
Section 3 Review
• What is the Human Genome Project?
• Compare a linkage map and a sequencing
map.
• What is the goal of gene therapy?
• Explain why DNA fingerprinting can be
used as evidence in law enforcement.
• Describe some possible benefits of the
Human Genome Project