Genetic fingerprinting

Question 1

What are variable number tandem repeats (VNTRs)?

Answer 1

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

Question 2

Why are VNTRs useful in genetic fingerprinting?

Answer 2

● 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 3

Explain how genetic fingerprinting can be used to analyse DNA fragments

Answer 3

1. Extract DNA from sample (eg. blood cells) and amplify by PCR
2. Cut DNA at specific base sequences / recognition sites (either side of VNTRs) 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 / bind 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 4

Compare and contrast genetic fingerprinting with genetic screening

Answer 4

● 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

Question 5

Explain how genetic fingerprinting can be used to determine genetic
relationships

Answer 5

● More closely related organisms have more similar VNTRs, so more similarities in genetic fingerprints
● Paternity testing - father should share around 50% of VNTRs / bands with child (due to inheritance)

Question 6

Explain how genetic fingerprinting can be used to determine genetic
variability within a population

Answer 6

Differences in VNTRs arise from mutations, so more differences show greater diversity within a population

Question 7

Explain the use of genetic fingerprinting in the fields of forensic science

Answer 7

● Compare genetic fingerprint of suspects to genetic fingerprint of DNA at crime scene
● If many bands match, the suspect was likely present at the crime scene

Question 8

Explain the use of genetic fingerprinting in the fields of medical diagnosis

Answer 8

● Some VNTR patterns are associated with an increased risk of certain genetic
disorders eg. Huntington’s

Question 9

Explain the use of genetic fingerprinting in the fields of animal and plant breeding

Answer 9

● Shows how closely related 2 individuals are, so that inbreeding can be avoided
● Breed pairs with dissimilar genetic fingerprints