3.8.4.2. Differences in DNA between individuals of the same species can be exploited for identification and diagnosis of heritable conditions

Question 1

What are DNA probes?

Answer 1

Short single strands of DNA. Have specific base sequence that’s complementary to the base sequence of part of a target gene.

Question 2

What is a target gene?

Answer 2

The allele you’re looking for e.g. the allele that causes a genetic disorder.

Question 3

What are DNA probes used for?

Answer 3

To locate specific alleles of genes (e.g. on chromosomes) or to see if a person’s DNA contains a mutated allele that causes a genetic disorder.

Question 4

What will a DNA probe do to the target allele?

Answer 4

If the target allele is present in the sample of DNA, the DNA probe will bind (hybridise) to it.

Question 5

Why do DNA probes have labels attached?

Answer 5

So that it can be detected. There are 2 common types of label:

• radioactive
• fluorescent

Question 6

Radioactive labels

Answer 6

Detected using X-ray film

Question 7

Fluorescent lables

Answer 7

Detected using UV light

Question 8

How do DNA probes work?

Answer 8

• Sample of DNA digested into fragments using REE
• Separated using electrophoresis
• Separated DNA fragments transferred to nylon membrane and incubated with the fluorescently labelled DNA probe

Question 9

What happens if the allele is present?

Answer 9

The DNA probe will hybridise (bind) to it.

Question 10

Why is the membrane exposed to UV light?

Answer 10

To detect the fluorescent label, which will be present if the gene is present.