|
Every gene contains a unique
sequence of the four bases
adenine (A), cytosine (C),
guanine (G) and thymine (T).
We can test to see if a
specific gene is present in
a person’s genetic make-up
by searching for its unique
base sequence.
The search uses a
single-stranded piece of DNA
called a gene probe. The
design of a probe uses the
fact that when DNA strands
pair up, A only pairs with T
and C only pairs with G. The
base sequence of the probe
matches the unique sequence
in the gene that the probe
is designed for.
To test a DNA sample
using a gene probe, the DNA
is first treated so that
each of the double-stranded
DNA molecules unzips into
single strands. The probe is
then added to the solution.
Because of the way the bases
pair up, the probe will
attach itself only to the
section of DNA that contains
a base sequence that matches
the probe’s sequence.
Here, cells are
stained with a fluorescent
dye which attaches to
chromosome 18. These cells
all contain an extra copy of
chromosome 18 which is known
as Edward syndrome. This is
called FISH - fluorescent in
situ hybridisation.
|
