LR and parentage testing

• define LR

  Weighing of the assessment of 2 mutually exculsive propsostions

  1. inclusionary: Hp: DNA orginates from POI
  2. exulsionary: Hd: DNA does not originate from POI
• why is LR Important

  due to there being no situation which probability does not have an assumption
• list the relevant case information for propositions

  1. alleged activities
  2. location of scene
  3. consenual partners
• what is irrevelant info

  1. prior convictions
  2. motive
  3. other forensic evidence
  4. responsibilies of the judge and jury
• bayes theorm

  • evidence interpretation
  • 100 billion times more likely
  • demostrates distinction between judge, jury and scientist is
• LR =1


  posterior evidence has no change

  • evidence is neutral and inconclusive
  • occurs in partial profiles
• LR >1


  supports Hp
• LR <1 


  Supports Hd
• equation for LR


  1/hd
• establishing major and minor peaks

  • calaculte peak height ratio
  • peaks should be 60+ for a major
• guidance for setting propositions

  1. mutually exculsive - both cannot occur at same time
  2. help address the issue
  3. state number of contributors and realtionship
  4. close exhasutive: unrelated indivi
• conditioning profiles 


  DNA profile of indiv assumed to be contributor of DNA obatined by evidenatry item in both prop
• assumed contributor 


  DNA on an item is expected
• how to determine of conditioning is required

  sample collected from exclusive
• steps for conditioning

  1. state information and assumptions
  2. state propositions
  3. state LR
  4. be prepared to change it
• 2 types of paternity testing

  1. parentage testing
  2. reverse paternity testing
• parentage testing

  alleles from mother and child to find alleged father
• reverse paternity testing

  alleles from mother and father to find child
• 3 possibilities for interpreting results

  1. exclusion: DNA is not originated
  2. inconclsuive: DNA is unable to be determined
  3. failure to exclude: DNA could originate
• PI


  paternity index, LR for maternity testing
• when do we further analysis the results

  when alleged father is not excluded
• name for alleged farther

  putative father
• what do we look at if relative is invloved

  theta as it helps with interbreeding and closely tight populations
• steps to determine PI

  1. find obligate alleles: alleles inherited from father
  2. equation
• theta


  co-ancestory: measures probability that 2 alleles on indiv has at a particular locus are IBD
• IBD


  indentifical by descent, which means they are related.

  • 2 people have common ancestor
• identical by state 


  alleles are the same due to mutation/chance
• theta values

  • full sibs: 0.5
  • 2nd cousins: 1/16
  • sub-pop: 0.03-0.01
  • aboriginal pop: 0.05
• when do we use theta

  1. small towm
  2. small pop
  3. religious group
  4. indigenous group
  5. inbreeding
• AI

  avunclar index, when alleged farther is a relative
• locus with the highest mutation

  • VWA
  • FGA
  • D18
• Locus with the lowest mutation

  • TH01
  • TPOX
  • D16