Document Sample
genetic-fingerprinting Powered By Docstoc

Biology A-level: Applications of Genetic
Genetic Fingerprinting
Devised by Alex Jeffreys at Leicester University and now widely used in
forensic science and other uses of identification.

Different bands, resembling a supermarket bar code, are produced, which are
unique to any one individual, except identical twins.

DNA is obtained from the white blood cells, mixed with restriction
endonuclease, which 'cuts' the DNA into millions of fragments, but not the
repeated regions, which retain their original length.

The DNA fragments are then loaded into a slot at the end of an agarose gel.

An electric current is passed across the gel, with the positive electrode at the
furthest end from the fragments.

Since DNA molecules have a negative charge, they will migrate through the gel
towards the positive electrode. Larger fragments move more slowly than the
smaller ones. The result is a series of bands down the gel, but these are
invisible at this stage.

Since the gel is difficult to keep, the DNA bands are then transferred to a nylon
membrane, which is incubated overnight with radioactive probes.

The radioactive probes bind with the DNA that has repeating regions.

A sheet of X-Ray photographic film is laid over the membrane in total darkness.
The radiation will affect the film, which is later developed, as a photograph.

The developed film reveals the series of DNA bands, which are unique to an individual.

Genetic counselling
Many illnesses are now being traced back to particular defective genes. Some,
like Huntington's disease, only appear later in life - between 30 and 50 years
of age.

While pinpointing the genes responsible for these terrible diseases is a
breakthrough, it also poses a dilemma...

In the past, children who have a 50:50 chance of inheriting the disease faced a
long wait to find out if they have been affected. Now they can choose to be
tested, and then cope with the devastating news.

Screening tests can reveal whether an unborn child has Down's syndrome or
cystic fibrosis for example.

Termination of pregnancy may be a decision that parents have to face, and this
is where counselling is required, for such a difficult decision.

With high-risk parents, embryos may be produced outside the body (so called
''test-tube babies'') and after screening for defective genes, only normal
embryos are implanted.

Transplant surgery
Transplanting foreign tissue carried great risk of rejection by the body's
immune system. The patient faces the rest of their life with a cocktail of anti-
suppressant drugs.

There is a great shortage in organs suitable for transplantation, resulting in
may patients suffering or even dying before they get a chance to have the
transplant operation.


Organs from other animals can be used in human transplantation, but they
pose a potentially greater risk of rejection.

One way to avoid this is to change the chemical signature of the surface of the
organ. This is achieved by adding the human gene that produces the correct
chemical signals onto the surface of the organ so that the recipient's antibodies
recognise it as 'self'.