Download Biology 3201 - novacentral.ca

Biology 3201
Ch. 18 – Genetics Ahead
18.1 – Diagnosis and Treatment of Genetic Disorders
genetic counseling – a process where detailed information is gathered about a
family’s history through interviews, blood tests, and discussions with geneticists in order
to determine the risk of contracting certain genetic disorders.
Detecting genetic disorders:
1) amniocentesis – medical procedure in which a sample of cells from the
amniotic fluid is tested for abnormalities
2) chorionic villi sampling (CVS) – sampling of cells from the chorion to test for
genetic conditions in a fetus
3) fetoscopy – medical procedure that involves direct observation of the fetus with
an endoscope (long tube with a camera at one end)
4) genetic marker – any characteristic that provides information about an
organism’s genome
Treating genetic disorders:
1) screening and prevention – if a disorder is detected early enough, treatment and
lifestyle modifications can be made
2) surgery
→ cleft plates – physical development that results in a groove in the upper
lip and roof of the mouth
3) environmental control – lifestyle modifications
4) gene therapy – the process of changing genes to treat genetic disorders. Can
involve splicing out defective portions of a gene and replacing them with functional ones.
18.2 – The Sequence of Life
genetic engineering – the process of changing the existing DNA of an organism
Techniques used in genetic engineering:
1. Restriction Enzymes
→ restriction endonucleases – family of enzymes made by prokaryotic
organisms; these enzymes recognize a short sequence of nucleotides on a strand of DNA
and cut the strand at a particular point within a sequence
→ restriction site – specific location on a strand of DNA where a
restriction endonuclease will cut a strand of DNA
2. Recombinant DNA
→ recombinant DNA – segments of DNA from two different species that
are joined in the laboratory to form a single molecule of DNA
3. DNA Amplification
→ DNA amplification – the process of generating a large sample of a
target DNA sequence from a single gene or DNA sample
→ can be done 3 ways:
1) using a bacterial vector: use restriction endonucleases to insert a
gene in bacterial DNA. As the bacterial cells multiply, it copies its DNA and the inserted
gene.
2) using a viral vector: same as bacterial, except viruses are used
3) Polymerase Chain Reaction (PCR): almost entirely automated
method of replicating DNA that allows researchers to target and amplify a very specific
sequence within a DNA sample (see fig 18.10, p. 615)
4. Gel Electrophoresis (see fig 18.11, p. 617)
→ gel electrophoresis: method in which molecules travel through a gel
subjected to an electric current. It is used to replicate molecules according to mass and
charge, and enable fragments of DNA to be separated for analysis
→ DNA fingerprint: pattern of bands formed by using gel electrophoresis
on DNA fragments
→ DNA has a negative charge (due to phosphate groups), so the
fragments move away from the negative terminal and towards the positive terminal.
Smaller fragments move further.
5. DNA sequencing
→ chain termination sequencing: process used to sequence DNA. The
process is a modified form of PCR
→ first, the replicated segment of DNA is synthesized into a series of
small fragments, and the nucleotides at the end of each fragment is tagged with a
radioactive marker. When these fragments are run on a gel, they show a pattern of bands,
indicating the position of the tagged nucleotides (see fig. 18.12, p. 618)
The Human Genome Project
Human Genome Project (HGP) – joint effort of thousands of researchers from
laboratories worldwide that determined the sequence of the three billion base pairs that
make up the human genome
Important findings
→ 99.9% of all human DNA is identical. In other words, the differences
among individuals in the world are from differences in 1 out of 1000 nucleotides.
→ human genome has 35, 000 genes but we have 100, 000 different
proteins. Shows that DNA sequence alone is not only factor which controls
development.
18.3 – The Chimera: From Legend to Lab
Genetically modified organisms (GMOs) – an organism that has its genome
altered or changed in some way.
Genetically modified food (GMFs) - food sources that have its genome altered in
some way.
Examples of GMOs and GMFs:
1) corn
→ over ½ of the corn produced today contains recombinant DNA
→ for example, herbicide-resistant corn can be sprayed with
herbicide and not be harmed.
2) insulin-producing bacteria
→ in the past, insulin was only available from animal sources.
Now, it can be produced by bacteria
→ the gene for producing insulin is inserted into a bacterial vector,
copied, and used to produce a lot of insulin
3) rice
→ a new strain of genetically modified rice called golden rice
contains more beta carotene and iron than in regular rice
4) bacteria and pollution
→ some strains of bacteria can be modified to consume PCB
(polychlorinated biphenyls). These compounds are highly toxic and can build up in the
food chain
→ other special strains of bacteria can consume oil; can be used to
clean up oil spills
Risks associated with GMOs and GMFs
1) Environmental threats
→ some studies suggest that if herbicide-resistant plants are used, farmers
will used more herbicide. The extra herbicide can leech out into water supplies
→ risk of herbicide-resistant plants could cross-breed with weeds,
producing “superweeds”
2) Health effects
→ people concerned about long term health effects because no long term
studies done
3) Social and economic issues
→ people fear that since GMFs come from private companies, they would
start to have control over the world food supply
artificial selection – human selection of particular traits (ex. Faster horses, diseaseresistant plants, breeding of dogs, etc.)
Cloning
Clones – identical copy of an organism or a part of an organism
(see fig 18.22, p. 629)
→ in order to produce a clone from an adult animal, you must find a way to
reverse the process of cellular differentiation. In the case of Dolly, researchers stopped
the cell cycle in the udder cells before inserting their nuclei into the egg cells. This
procedure allowed the DNA in the differentiated udder nuclei to regain their potential to
generate other types of cells
Benefits of cloning:
1. speed of reproduction – occurs quickly
2. elimination of disease
Risks:
1.
2.
3.
4.
manipulation of treats
reducing genetic variability
embryo use and destruction
loss of individuality