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Biology 3201 Genetics

Unit #8Diagnosis and Treatment of Genetic Disorders

Genetic Engineering

The Human Genome Project

GMOs and GMFs

Cloning

Diagnosis of Genetic Disorders

• Detection of genetics disorders- Methods:

• 1. amniocentesis – fluid from amniotic sac is removed with a needle. Karyotype is

prepared along with other genetic tests to determine disorders.

• 2. CVS (chorionic villi sampling) – cells are removed from the chorion or placenta and

examined for genetic disorders

• 3. fetoscopy – camera is used to view the fetus to look for physical abnormalities that

may suggest genetic disorders

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Diagnosis of Genetic Disorders

• 4. genetic markers – these are indicators found in the DNA that indicate the

inheritance of a defective gene or a gene causing a disorder. There are two types of

markers:

• - linked markers: a known sequence of nucleotides located close to a gene that causes a

disorder

• Gene specific marker: a sequence of DNA that is part of the gene itself

Genetic markers are found using radioactive or fluorescent tags on complimentary DNA

nucleotide sequences of the suspected marker

Treatment of Genetic Disorders

• Methods:

• 1. genetic screening and prevention

• Blood and other biochemical tests are often done either at birth or prior to birth to determine genetic disorders

• Parents are often advised of options such as special diets, etc. they can place their children on.

• 2. surgery

• Surgery can repair some physical abnormalities caused by genetic conditions such cleft palate.

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Treatment of Genetic Disorders

• 3. environmental control

• This is the controlling of the environment in which an individual with a disorder lives.

• Ex. People with Albinism (lack of melanin – skin pigment) must avoid sunlight. These people usually are fully clothed all the night and go out at night, etc.

• 4. gene therapy

• A procedure in which normal or modified genes are transferred into defective cells of an individual.

• The new genes should cause the cells to work normally and “fix” the genetic disorder.

Ethical questions arising from the use of gene

therapy

• Are we playing God?

• Who gets the modified genes and who does not?

• For what conditions are the genes produced/used?

• What cost and who pays for the procedure?

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Genetic Engineering – Restriction Enzymes

• Genetic engineering: the manipulation of an organism’s genetic material to

modify the proteins it produces.

• Techniques involved:

• 1. restriction enzymes: these enzymes such as restriction endonucleases are used to

“cut” DNA into shorter pieces. Each fragment has “sticky ends” (short segments of

unpaired DNA bases) at each end of the fragment.

Restriction Enzymes

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Genetic Engineering – Recombinant DNA

• 2. recombinant DNA: a new segment of DNA made by combining or

joining DNA from two different sources.

• DNA which you want to insert into a new genome is cut using restriction enzymes,

along with the original DNA

• The sticky ends of the inserted gene pair with sticky ends of original DNA

Recombinant DNA

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Genetic Engineering – DNA Amplification

(cloning vectors)

• 3. DNA Amplification

• The process of generating a large sample of DNA from a single gene or DNA

fragment

• Two methods used in this process

• (1) cloning vectors: use of a bacteria or virus to produce many copies of a foreign

DNA sequence. Foreign DNA is spliced into the DNA of either a virus or bacteria

and they are allowed to reproduce. The DNA is then harvested from the bacteria or

virus at a later time.

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Genetic Engineering – DNA amplification

(PCR)

• (2) Polymerase Chain Reaction (PCR): an automated method of reproducing DNA by using enzymes such as DNA polymerase and primers

• Steps:

• DNA section is placed in a solution of free nucleotides (the free nucleotides are used to make copies of the DNA section)

• Heated to open the double helix

• DNA polymerase is added and DNA replication occurs

• Cycle is repeated several times

• End result is lots of DNA sequence that is wanted

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Genetic Engineering – Gel Electrophoresis and

DNA Sequencing

• Fragments of DNA are separated according to their mass and electrical charge

• On one end of a gel plate a sample of DNA fragments is placed. The gel is given an electric current causing it to become polarized on the other end. The fragments are negatively charged and they are attracted to the other end of the gel. The fragments move according to their mass. The smaller fragments move more quickly toward the opposite end of the gel.

• After a while a characteristic pattern of bands emerges. This is known as the DNA FINGERPRINT of a person

• DNA sequencing: the process of reading DNA fragments so as to determine the exact sequence of base pairs in a sample of DNA

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The Human Genome Project

• A 13 year project aimed at sequencing the entire human genome.

• Several scientists from around the world worked on the project

• Completed in 2003

• 3 billion base pairs were sequenced

• Why was it done?

• Scientists thought that id we could know the entire sequence of the human genome we could determine and cure disorders that affect the human population

• Our DNA could be compared to other organisms

Major Findings of the Human Genome Project

• (1) 99.9 % of all human DNA is identical

• (2) there are approximately 35000 genes in the human population. Much less

than the expected 100, 000.

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Risks and Benefits of the Human Genome

Project

• Risks

• Privacy – all of genome is known, so your DNA is not so “unique” anymore

• Financial – if genetic disorders can be determined to exist in population, can insurance be cancelled, denied, etc. Employment, ???

• Ethical – should we be playing God?

• Benefits

• Knowledge of predisposition to disease – we know about the predisposition to disease so treatments and/or preventions can be implemented

• Analysis of diseases – diseases that are known can be analysed and preventions/cures created

Genetically Modified Foods and Organisms

• GMO = genetically modified organisms

• GMF = genetically modified foods

• Most GMFs and GMOs are transgenic (genes are moved/altered)

• Examples

• Herbicide resistant corn

• Cows with high milk production

• Golden rice (high amounts of vitamin A and iron)

• Transgenic salmon

• Insulin producing bacteria

• PCB eating bacteria

• Oil eating bacteria

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Risks/Benefits of GMOs and GMFs

• Risks

• More herbicides used

• If genes spread to wild organisms could affect biodiversity

• Could create superbugs (immune to pesticides)

• Benefits

• Alleviate world hunger

• Employment for more farmers, etc.

Cloning

• Cloning: the production of an organism that is genetically identical to another.

• Ex. Dolly the sheep

• Benefits and Risks

• Elimination of disease

• Speed of production

• Manipulation of traits

• Reducing genetic variety (all are alike)

• Embryo destruction and use – ethics???

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Therapeutic vs. Reproductive Cloning

• Therapeutic cloning: the culturing of human cells for use in treating medical

disorders

• Ex. Using cloned pancreatic cells to cure diseased cells of the pancreas

• Reproductive cloning: the development of a cloned embryo for the purpose

of creating an entire organism

• Ex. Dolly the sheep