A question from Lorry Gregory: AP Biology homework help about Cystic Fibrosis?
Cystic fibrosis can be caused by any one of several mutant alleles of the cystic fibrosis gene. The most common of these mutants alleles accounts for about 70% of cases of cystic fibrosis. The use of gene probes can identify individuals carrying this allele. Gene probes are single strands of DNA which are radioactively labelled. They have a base sequence that is complementary to a mutant allele. The main stages in using a gene probe are shown in the diagram.
Sample of DNA extracted from a person’s tissue and heated to separate the strands.
Radioactive gene probe is added to the DNA.
Excess probe is washed away.
Sample is tested for radioactivity.
Using the information given, explain how the use of a gene probe could enable the presence of a mutant allele of the cystic fibrosis to be detected.

Chosen answer:

Answer by Horst S
With your approach, you can only identify those mutations that you actually test for.
You take a sample of your extracted DNA and separate it into various aliquots. Each aliquot is individually hybridized with a probe specific for each mutation. This can be done by Southern Hybridization. You will get a signal when your sequence binds (hybridizes) with the probe. No signal means that mutation is absent – the probe could not bind.

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