8.4.3 genetic fingerprinting

What are variable number tandem repeats (VNTRs)

• repeating sequences of nucleotides/ bases

• Found within non-coding sections of DNA at many sites throughout an organisms genome

Why are VNTRs useful in genetic fingerprinting

• probability of two individuals having the same VNTRs in very low

• As an organisms genome contains many VNTRs and lengths at each loci differ between individuals

How can genetic fingerprinting be used to analyse DNA fragments

1. Extract DNA from sample 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 (X ray) if a radioactive probe was used

Similarities between genetic fingerprinting and genetic screening

• both use PCR to amplify DNA sample

• Both use electrophoresis to separate DNA fragments

• Both use labelled DNA probes to visualise specific DNA fragments

Differences between genetic fingerprinting and genetic screening

genetic fingerprinting analysed VNTRs whereas genetic screening analyses specific alleles of a gene

How can genetic fingerprinting be used to determine genetic relationships

• 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

How can genetic fingerprinting be used to determine genetic variability within a population

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

How is genetic fingerprinting used in forensic science

• compare genetic fingerprint of suspects to the genetic fingerprint at the crime scene

• If many bonds match, the suspect was likely present at the crime scene

How is genetic fingerprinting used in Medical diagnosis

• some VNTR patterns are associated with an increased risk of certain genetic disorders

How is genetic fingerprinting used in Animal and plant breeding

• shows how closely related 2 individuals are, so that interbreeding can be avoided

• So they breed pairs with dissimilar genetic fingerprints