UNIT 2:  MOLECULAR GENETICS

 

E.  Medical Applications

 

·         most of today’s medical practices don’t only deal with treatment of diseases, but also prevention

·         the earlier a disease is detected, the faster an aggressive treatment may curb its effects

·         for example, traditional testing for HIV exposure has been to detect antibodies that the immune system has produced in response to virus exposure

·         although very effective in detecting whether or not the individual has been exposed to HIV, this procedure requires that a certain amount of time transpires so the immune system can accumulate enough antibodies to show up on the test

·         recently, the use of PCR has proven to detect the virus that causes AIDS – this technique tests for the presence of the virus itself, rather than the antibodies made to fight it, which means that a person does not need to wait a few months until the antibodies are detectable in the blood

·         genetic screening is the detection of mutations known to be associated with genetic disorders before they manifest themselves in an individual

·         such diseases as Huntington’s chorea can be detected before symptoms of the disease surface

·         other kinds of genetic disorders that can be detected are those in the human fetus

·         embryonic cells from the amniotic fluid can be tested during gestation for genetic disorders such as hemophilia, phenylketonuria, cystic fibrosis, and Duchenne’s muscular dystrophy

·         genetic screening technology and accuracy has improved since the completion of the Human Genome Project – with increased knowledge of the location of specific genes, genetic screening will become more and more useful in detecting disorders before they occur

·         gene therapy – the alteration of a genetic sequence in an organism to prevent or treat a genetic disorder, is in its early stages and has had a limited success in the treatment of a few diseases

·         this kind of therapy is being developed as a technique to cure chronic pain

·         the body deals with pain on one of two ways, both of which involve neurotransmitters – specialized molecules that target receptor sites on the ends of nerve cells

·         pronociceptive transmitters induce pain, whereas antinociceptive transmitters inhibit the sensation of pain

·         the effects of these neurotransmitters eventually relay a message to the brain via chemical messengers that either heighten or dampen the feeling of pain

·         if a gene is inserted into a cell that expresses antinociceptive transmitters, more of these molecules will be made, resulting in the minimization of pain

·         another strategy that modifies gene expression via gene therapy, thereby controlling pain is called antisense synthetic oligonucleotide therapy – antisense synthetic oligonucleotides are short stretches of DNA or RNA that recognize and deactivate complementary mRNA molecules by hybridizing with them

·         antisense RNA that is complimentary to the pronociceptive transmitter mRNA will hybridize with it, preventing ribosomes from translating it into protein – basically, the expression of the pronociceptive gene is blocked

 

 

F.  Agricultural Applications

 

·         by 1981, transgenic plants were made – foreign genes were introduced to plant cells using a Ti plasmid (tumor-inducing plasmid) vector found in the soil bacteria Agrobacterium tumefaciens

·         the bacteria enter the plant tissue via a plant wound, and transformation is natural

·         the result is a bulbous growth called a crown gall (see Figure 2, p. 306)

·         the relationship is true commensalisms – the bacteria gets food and nutrients from the plant and the plant neither benefits nor suffers harm

·         since this discovery, many different kinds of transformations have been successfully performed

·         plants have been genetically modified to produce greater yields, to make hardier plants, to produce uniformity in plant characteristics, to make insect and virus resistant strains, and to make herbicide tolerant species

·         one very famous successful transformation, was the insertion of the gene that prevented the expression of polygalacturonase – the enzyme that is responsible for ripening fruit was limited to only 1% expression

·         an American company has found a way to insert a gene into a cotton plant that results in the production of a polyester polymer inside cotton fibre – the result is a plant that produces a cotton-polyester blend – a natural, environmentally-friendly system for synthesizing a polymer

·         although these transgenic crops have improve the quality of our lives in certain areas, the damage that they can potentially cause to the environment may far outweigh their benefits

·         the concern is there since the repercussions of such biological tampering may take decades to surface

·         the ecological ramifications may be substantial enough to seriously reconsider this technology

·         genetic engineering technology can also affect the economy as well – for example, a hormone called bovine somatotropin, which boosts milk production in cows by 10%, may in fact help drop the price of milk, which in turn, affects diary farmer profits throughout the entire Country

·         since 1994, 40 genetically modified foods have been approved in Canada

·         approximately 60% of all foods found in groceries today contain food that has been genetically modified

 

G.  Forensics

 

·         the first court case that involved the use of FRLP took place in 1987, in England

·         a man was convicted when the DNA of semen collected at a rape scene was compared to his DNA

·         the only fact that can be determined by DNA fingerprinting is that the sample containing the DNA tested came from a particular suspect in question – whether or not the person committed the crime must be supported by further collaborating evidence

·         both PCR and RFLP are used in criminal investigations, depending on the state of the DNA sample

·         RFLP requires large samples that are undegraded, whereas PCR can be performed with minute quantities that are degraded

·         both techniques produce the distinct and unique pattern of bands, called DNA “fingerprints”, and both techniques take advantage of the noncoding regions of the DNA

·         noncoding regions of one individual will posses specific variable number tandem repeats, different from any other individual, and can therefore be used as a basis for discriminating between individuals

·         the probability of matching six to seven areas of noncoding regions with another person could be as low as one in a billion

 

Homework:       1-3, p. 309