8.4.3 genetic finger printing

• what are variable number tandem repeats (VNTRs)

  repeating sequences of nucleotides / bases (eg GATA)

  found within non-coding sections of DNA at many sites throughout an organism’s genome
• why are VNTRs useful in genetic fingerprinting

  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
• explain how genetic fingerprinting can be used to analyse DNA fragments

  extract DNA from sample and amplify by PCR

  cut DNA at specific base sequences (either side of VNTRs) using restriction enzymes

  separate VNTR fragments according to length using gel electrophoresis (shorter travel further)

  transfer to a nylon membrane and treat to form single strands with exposed bases

  add labelled DNA probes which bind with complementary VNTRs

  to show bound probe expose membrane to UV light if a fluorescently labelled probe was used or use autoradiography if a radioactive probe was used
• compare and contrast genetic fingerprinting with 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

  genetic fingerprinting analyses VNTRs whereas genetic screening analyses specific alleles of a gene
• how genetic fingerprinting can 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 genetic fingerprinting can be used to determine genetic variability within a population

  differences in VNTRs arise from mutations, so more differences show greater diversity within a population
• use of genetic fingerprinting in the field of forensic science

  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
• use of genetic fingerprinting in the field of medical diagnosis

  some VNTR patterns are associated with an increased risk of certain genetic disorders eg huntington’s
• use of genetic fingerprinting in the field of animal and plant breeding

  shows how closely related 2 individuals are

  so that inbreeding can be avoided

  breed pairs with dissimilar genetic fingerprints