Genetic screening

Question 1

What are DNA probes

Answer 1

● Short, single stranded pieces DNA
● Base sequence complementary to bases on part of a target allele
● Usually labelled with a fluorescent or radioactive tag so can be identified

Question 2

Why are probes just longer then a few bases

Answer 2

Longer sequences only likely to occur in target allele

Question 3

DNA hybridisation

Answer 3

Binding of single stranded DNA probe to complementary single strand of DNA
● Forming hydrogen bonds / base pairs

Question 4

How do you carry out genetic screening

Answer 4

1. Extract DNA and amplify by PCR
2. Restriction enzymes cut DNA at specific base sequences (either side of target gene)
3. Separate fragments by gel electrophoresis according to length
4. Transfer to a nylon membrane and treat to form single strands with exposed bases
5. Labelled DNA probe will hybridise with its target allele (then wash to remove unbound probe)
6. To show bound probe either:
   ● Expose membrane to UV light if fluorescently labelled probe used
   ● Use autoradiography (expose to X ray film) if radioactive probe used