Chapter 13 – Genetic
Engineering
L2 Biology
Has Bonnie been bred by selective breeding?
Selective Breeding
• Choose organisms with the desired traits
and breed them, so the next generation also
has those traits
• Nearly all domesticated animals and crops
• Luther Burbank (1849-1926) developed
>800 diff varieties of plants in his lifetime
Hybridization
• Breed two dissimilar organisms
• In plants – often results in better lines – hybrids are larger, stronger,
etc
• In animals – hybrids produced may be weaker and sterile
– Ex – wolf x dog ---- weak wolf-dog
– Ex – horse x donkey ---- mule (sterile)
Lion x Tiger = Liger
Horse x Donkey = Mule
Inbreeding
• Breeding two organisms that are
very similar to produce offspring
with the desired traits.
– Ex – dog breeds
•Risks – might bring together two
individuals that carry bad recessive genes –
many purebred dogs have genetic disorders
that mutts don’t get.
Increasing Variation
• Induce mutations – the ultimate source of
genetic variations among a group of
organisms
– Mutagens used – radiation and chemicals
– Some organisms are formed that have more
desirable variations.
Producing new kinds of bacteria
• Can expose millions of bacteria at one time
to radiation – increases chances of
producing a successful mutant.
– Ex – bacteria that can digest oil have been
produced this way
Producing new kinds of plants:
• Drugs that prevent chromosomal separation
in meiosis have been used to create plants
that have more than two sets of
chromosomes (2n). These are called
polyploid plants.
– Ex – bananas, citrus fruit, strawberries, many
ornamental flowers
Diploid corn
Tetraploid corn
Manipulating DNA – tools of the
molecular biologist
• DNA extraction – open the cells and
separate DNA from all the other cell parts.
– Remember the kiwi lab?
• Cutting DNA
• Use restriction enzymes
– each one cuts DNA at a
specific sequence of nucleotides.
• This will make different
lengths of DNA
• Separating DNA – Gel Electrophoresis
– Place fragments at one end of a porous gel – we
use agarose gel
– Apply an electric current – The DNA is
negatively charged and will travel toward the
positive end of the gel.
– The larger pieces of DNA move slower, the
smaller ones faster.
– Used to compare genomes of different
organisms or different individuals.
– Also used to locate and identify one particular
gene out of an individual’s genome.
Click here for animation about
gel electrophoresis
Using the DNA Sequence
• Sequence can be read, studied, and changed.
• Techniques used to study DNA sequences:
– Use DNA polymerase and the 4 DNA bases to
produce a new DNA strand complementary to
unknown strand – some of the bases are dyed.
• Dye-labeled strands are then separated using gel
electrophoresis and the order of the bands tells the
DNA sequence of the unknown strand.
• Cutting and Pasting – make recombinant DNA (DNA from
two different organisms).
– Cut out the gene to be inserted, use same restriction
enzyme to cut the receiving DNA strand, attach the two
DNA strands
Making Copies
• Polymerase Chain Reaction (PCR) is used
to make many copies of the same piece of
DNA like a photocopy machine makes
copies of papers.
• This is useful if there is only a very small
sample of DNA available (as that found in a
small blood drop at a crime scene)
Cell Transformation
• A cell takes in DNA from outside the cell
and that DNA then becomes part of the
cell’s DNA.
• Bacteria – place DNA in the solution that
bacteria live in, and some of that DNA will
be taken in by the bacteria cells.
Bacteria Transformation using
Recombinant DNA
• Cut a gene with a restriction enzyme out of a
human cell (ex – gene for insulin or growth
hormone work well)
• Cut a bacterial plasmid using the same restriction
enzyme (DNA ends will be complementary)
• Insert Human gene into bacterial plasmid
• Insert plasmid back into bacterial cell
• Bacteria will multiply, and all offspring will have
that gene – these bacteria will then follow the
directions of the human gene and make the protein
coded for (insulin or human growth hormone)
Transforming Plant Cells
• Use bacterial plasmid to insert desired gene
into DNA of a plant
Transforming Animal Cells
– Directly inject DNA into the nucleus of an egg
– it will become part of the chromosomes.
• Has been used to replace specific genes.
Glowing mouse cells in
embryos that were made
from sperm given the gene
for bioluminescence from
jellyfish – now all the cells
glow!
Applications of Genetic
Engineering
• Gene for luciferase was isolated from
fireflies and inserted into tobacco plants –
they glowed!
• Transgenic organisms – contain genes from
other species
A transgenic mouse,
which carries
a jellyfish gene,
glows green under
fluorescent light.
Transgenic Organisms
• Bacteria - Make human proteins like insulin
• Plants – 52% of soybeans, 25% of corn in
US in year 2000. Some produce natural
insecticide, some resist weed-killers, may
soon be used to produce human antibodies;
rice with vitamin A.
•Animals – mice
with immune
systems like
humans; farm
animals that grow
faster and larger
with extra copies of
growth hormone
genes; animals with
leaner meat;
chickens resistant to
bacterial infections.
Cloning
• Clone – member of a population
of genetically identical cells
produced from a single cell.
• 1996 – Dolly cloned –
1st mammal (sheep) cloned.
• She got arthritis several years
earlier than most sheep
• Died in 2003