genetic fingerprinting probes

Question 1

dna probe

Answer 1

Short, single stranded pieces of DNA
With a base sequence complementary to bases on part of a target allele / region
Usually labelled with a fluorescent or radioactive tag for identification

Question 2

dna hybridisation

Answer 2

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

Question 3

genetic screening to locate specific allele

Answer 3

1. Extract DNA and amplify by PCR
2. Cut DNA at specific base sequences using restriction enzymes
3. Separate DNA fragments / alleles (according to length) using gel electrophoresis
4. Transfer to a nylon membrane and treat to form single strands with exposed bases
5. Add labelled DNA probes which hybridise / bind with target alleles (& wash to remove unbound probe)
6. To show bound probe, expose membrane to UV light if a fluorescently labelled probe was used
   OR use autoradiography (expose to X-ray film) if a radioactive probe was used

Question 4

gel electrophoresis

Answer 4

● A method used to separate nucleic acid (DNA / RNA) fragments OR proteins
● According to length / mass AND charge

Question 5

how does gel electrophoresis separate dna fragments

Answer 5

DNA samples loaded into wells in a porous gel and
covered in buffer solution (which conducts electricity)
Electrical current passed through → DNA is negatively
charged so moves towards positive electrode
3. Shorter DNA fragments travel faster so travel further

Question 6

How can data showing results of gel electrophoresis be interpreted?

Answer 6

Run a standard with DNA fragments / proteins of known lengths under the same conditions
Compare to position of unknown DNA fragments / proteins to estimate their size
Shorter DNA fragments/ proteins travel further / faster

Question 7

Describe examples of the use of labelled DNA probes

Answer 7

● Screening patients for heritable conditions
● Screening patients for drug responses
● Screening patients for health risks

Question 8

Describe the role of a genetic counsellor

Answer 8

1. Explain results of genetic screening, including consequences of a disease
2. Discuss treatments available for genetic condition
3. Discuss lifestyle choices
4. Explain probability of condition / alleles being passed onto offspring →
   enable patients to make informed decisions about having children

Question 9

What is personalised medicine?

Answer 9

● Medicine tailored to an individual’s
genotype / DNA
● Increasing effectiveness of treatment

Answer 10

✓ Can enable people to make lifestyle choices to reduce chances of diseases developing
✓ Allows people to make informed decisions about having their own biological children
✓ Allows use of personalised medicines, increasing effectiveness of treatment
X Screening for incurable diseases or diseases that develop later in life may lead to depression
X Could lead to discrimination by insurance companies / employers
X May cause undue stress if patient does not develop the disease

Question 11

what’s VNTRS

Answer 11

● Repeating sequences of nucleotides / bases
● Found within non-coding sections of DNA at many sites throughout an organism’s genome

Question 12

Why are VNTRs useful in genetic fingerprinting?

Answer 12

● Probability of two individuals having the same VNTRs is very low
● As an organism’s genome contains many VNTRs and lengths at each loci differ between individuals

Question 13

Explain how genetic fingerprinting can be used to analyse DNA fragments

Answer 13

1. Extract DNA from sample and amplify by PCR
2. Cut DNA at specific base sequences using restriction enzymes
3. Separate VNTR fragments according to length using gel electrophoresis (shorter ones travel further)
4. Transfer to a nylon membrane and treat to form single strands with exposed bases
5. Add labelled DNA probes which hybridise with complementary VNTRs (& wash to remove
   unbound probe)
6. To show bound probe, expose membrane to UV light if a fluorescently labelled probe was used
   OR use autoradiography (expose to X-ray film) if a radioactive probe was used

Question 14

Compare and contrast genetic fingerprinting with genetic screening

Answer 14

● Both use PCR to amplify DNA sample
● Both use electrophoresis to separate DNA fragments
● Both use labelled DNA probes to visualise specific DNA fragments
● Genetic fingerprinting analyses VNTRs whereas genetic screening analyses specific alleles of a gene