3.8.4.2 Differences in DNA between individuals of the same species can be exploited for
identification and diagnosis of heritable conditions – AQA A Level Biology Summary Notes
Use of labelled DNA probes and DNA hybridisation to locate specific alleles of genes
DNA probe
- Piece of single stranded DNA with base sequence that is complementary to a specific allele
you wish to identify
- Probe is labelled with radioactive or fluorescent tag
To use DNA probe, DNA sample is heated or placed in alkali
Causes DNA sample to become single stranded
DNA probe is added to main DNA sample
If DNA sample is complementary to DNA sample (ie DNA sample contains allele of interest) then the
probe will complementary base pair and bind to sample – this is DNA hybridisation
Sample then washed to remove unbound probe
DNA is colourless so to determine whether or not the probe has bound to DNA sample, the results
are visualised using laser (fluorescent tag on probe) or autoradiogram (radioactive tag on probe)
Application about DNA probs and DNA hybridisation
Application 1 – Soutern Blot
- DNA/RNA fragments seperated by size via gel electrophoresis
- Then identify if DNA fragments contain given allele
- Cannot directly add DNA probe to gel
- So DNA from gel is imprinted and transferred onto solid support (nitrocellulose or nylon
paper)
- This paper is then unproved
identification and diagnosis of heritable conditions – AQA A Level Biology Summary Notes
Use of labelled DNA probes and DNA hybridisation to locate specific alleles of genes
DNA probe
- Piece of single stranded DNA with base sequence that is complementary to a specific allele
you wish to identify
- Probe is labelled with radioactive or fluorescent tag
To use DNA probe, DNA sample is heated or placed in alkali
Causes DNA sample to become single stranded
DNA probe is added to main DNA sample
If DNA sample is complementary to DNA sample (ie DNA sample contains allele of interest) then the
probe will complementary base pair and bind to sample – this is DNA hybridisation
Sample then washed to remove unbound probe
DNA is colourless so to determine whether or not the probe has bound to DNA sample, the results
are visualised using laser (fluorescent tag on probe) or autoradiogram (radioactive tag on probe)
Application about DNA probs and DNA hybridisation
Application 1 – Soutern Blot
- DNA/RNA fragments seperated by size via gel electrophoresis
- Then identify if DNA fragments contain given allele
- Cannot directly add DNA probe to gel
- So DNA from gel is imprinted and transferred onto solid support (nitrocellulose or nylon
paper)
- This paper is then unproved
