Forensic Geneaology Flashcards
During the Pitchfork case, Jeffreys uses a type of repeating DNA sequence, different to the ones used today. The repeated segments in this case dozens or even 100 bases long can be observed. These are referred to as?
Minisatellites
What are minisatellites?
- highly variable sequences (STRs)
- non-coding
- repeated within the gene
- sometimes called variable number tandem repeats (VNTR)
- between 9-80 base pairs
What us familial searching?
- uses the NDNAD to identify individuals who have genetic potential to be related to the individual who left the crime scene profile
- can be used to identify potential suspects who are not in the database
Why might there be no match on the NDNAD?
- person may have moved abroad
- interpol searches
- person may be in prison/hospital institution
- mental health act
- person mat not have re-offended
- person re-offending in a category of crime not routinely sampled by a force
- crime may not have been reported
- person has died
- person was never caught
What other tools may be used if there is no match on the database?
- familial searches
- Y STR
- rare allele mapping
- intelligence led screens
What case showed how familial searching works?
Joseph Kappen
* NDNAD searched for profiles of possible relatives
What is family dispersion correlated with?
- higher income
- higher educatio
- criminality runs in families
- offenders operate close to where they live or in an area they are familiar with
How is familial searching done?
look for 2 types of relatives using two different computer programmes
* parents or children of offender
* siblings of offender
How are siblings used for familial searching?
- siblings have the same parents
- get 50% of our DNA from each parents
- likely to share more DNA with each other than with unreleated individuals
How are Y-STR’s used in familial searching and screening?
- if a male appears on the familial lists as a possible parent, child or sibling of the offender, in order for this to be true, his Y-STR must match that of the crime scene stain
- if it doesnt, all his male siblings , father and sons are eliminated as possible offenders
How is mitochondrial DNA used in familial searching?
- if a female appears as a possible parent or sibling of the offender, for that to be true, her mitochondrial DNA profile must match that of the crime scene stain
- if it doesnt match all her siblings and children are eliminated as possible offenders but her father is not eliminated
What are the results from familial searching?
each computer program will produce a list of profiles:
* parent/child list - profiles have at least one matching DNA band at each of the 17 loci
* sibling list: a list with the number of matching bands
How are likelihood ratios used in familial searching?
- represents how likely an individual is to be related to the offender
- calculated based on which alleles the individual shares with the offender and how rare these are in the general population
- higher the number, the more likely that person is related
What are some case specific parameters for prioritisation of the results list?
- ethnic appearance - witness statements & ethnic inference results
- age
- parent/child - must be at least 15 years older/younger
- siblings - no more than 20 years older/younger
- geography - need to be relevant areas
How do crime scene investigators collect samples from the perpetrator?
- blood, semen, hair and other cellular material
