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Study Guide Chapter 13: Genetic Engineering
13-1 Selective Breeding
Selective breeding has been used by humans for thousands of years
to increase the incidence of desirable traits from a variable population
and produce domestic animals and crop plants. Dog breed
characteristics are maintained by inbreeding between dogs of the
same characters. Excessive inbreeding also increases the incidence of
double-recessive genetic defects in a breed.
Breeders increase genetic variation in bacteria by radiation, or by
using drugs in plants to increase polyploidy (chromosome sets) during
meiosis. Polyploidy in plants increases productivity (but it kills
animals). Bananas are an example of a polyploid crop.
13-2 Manipulating DNA
Scientists use restriction enzymes such as EcoRI (also called “DNA
scissors”) to cut DNA into smaller pieces that usually have “sticky ends” at
specific base sequences. The sticky ends are ready to hydrogen-bond with a
complementary set of bases at the end of another single chain.
Gel electrophoresis uses electricity to separate DNA segments by length
(and charge). Restriction enzymes are used to cut the DNA pieces before gel
electrophoresis. Gel electrophoresis produces a DNA fingerprint of bands by
base size. Bases are ATCG (Understand this in detail).
DNA fingerprinting uses gel electrophoresis to identify DNA samples. The
samples are cut with restriction enzymes, a gel is run, and the bands of the
gel are compared with known DNA. Different DNA strands produce A unique
pattern of bands.
DNA sequencing is a procedure where the order of bases on a specific DNA
strand can be identified. This takes lots of computers and robots. (More
details are not required).
PCR is polymerase chain reaction. This is a process whereby a minute
amount of DNA from a small tissue sample can be multiplied into a large
enough quantity that can be used for analysis. PCR uses DNA polymerase
from a bacteria scooped up in a Yellowstone National Park hotspring.(More
details are not required).
13-3 Cell Transformation
Cell transformation occurs when a cell’s DNA is changed by inserting a gene
from another species using genetic engineering. Cell transformation only
works in a small % of cells. Genes may be inserted in the wrong place,
producing unexpected proteins (possible allergens), and weird offspring.
To transform a bacterium:
Step 1 A restriction enzyme is used to cut a gene such as human
insulin out of a DNA strand. The gene has sticky ends.
Step 2 A bacterial plasmid is taken out of its cell and the circle is cut
open using a restriction enzyme. The cut plasmid has sticky ends.
Step 3 The gene and a genetic marker gene are inserted into the
plasmid, sticking to the ends where the bases pair up exactly. DNA
from two completely different organisms is called recombinant DNA.
Step 4 The plasmid is put back into the bacterium. In one sample, a
small percentage of bacteria are transformed. The rest do not change.
Therefore the genetic marker gene is used to identify the transformed
bacteria.
Step 5 The transformed bacterium can then be “farmed” to produce
very large quantities of the protein, such as human insulin, coded for
by the gene.
Three ways to transform a plant:
Step 1 Replace the cancer gene of a cancer-causing bacterium
(Agrobacterium tumefaciens: no need to learn name) with the gene
and marker you want to insert.
Step 2 Infect the plant cell with the bacterium.
Step 3 Some plant cells will take up the recombinant plasmid and
express the gene.
Step 4 Grow the plants as clones from the tissue.
OR
Step 1 Remove plant cell walls.
Step 2 Put gene and marker into the tissue culture.
Step 3 Some plant cells will take up the gene.
Step 4 Grow the plants as clones from the tissue.
OR
Step 1 Use a gene gun to fire genes wrapped in special pellets at
plant tissues.
Step 2 Some plant cells will take up the gene.
Step 3 Grow the plants as clones from the tissue.
Ways to transform an animal, as detailed above:
Infect the animal cell with a transformed bacterium or retrovirus. The
DNA becomes part of the animal nucleus. This can be used for gene
therapy of tissues. But not all cells are transformed and the whole
animal is not cured. Need to clone to get offspring.
OR
Inject the nucleus of a large egg cell with a recombinant DNA gene
and a marker, and hope that this gets “mended” into the DNA. Since
this is an egg cell, the animal will grow when fertilized or cloned. Not
all the offspring will be transformed.
13-4 Applications of Genetic Engineering: Biotechnology
An organism that grows from recombinant DNA taken from different
species is called a transgenic organism.
Transgenic animals include “knockout” organisms (p329). A knockout mouse
has genes for a specific trait turned off (knocked out) so we can study how
that particular gene works. Transgenic animals can help solve human genetic
problems.
Transgenic plants are also called GM crops (GM for genetically modified).
25% US corn is GM corn. Inserted genes may include a gene for resistance to
weedkiller, or a gene that produces insecticide. The goal is usually to
increase the food supply. Golden rice has a gene to produce vitamin A to
reduce vitamin deficiency and childhood blindness in poor countries.
A clone is a member of a population of genetically identical cells and comes
from a single body cell. Clones of multicellular organisms include sheep
(Dolly was the first mammal clone). Dolly developed from a single body cell.
The donor nucleus of this cell was put into an egg cell without a nucleus, and
grew.