Forensic Investigative Genetic Genealogy

Question 1

during the Pitchfork case, Jeffreys used a type of repeating (DNA) sequences, 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?

Answer 1

minisatellites

Question 2

What are minisatellites

Answer 2

• highly variable sequences (STRs)
• non-coding
• repeated within gene
• sometimes called variable number tandem repeats (VNTRs)
• range between 9 and 80 base pairs
• approximately 60 % of non-coding DNA consists of short sequences repeated over and over

Question 3

What is familial searchiing?

Answer 3

• 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

Question 4

What might cause no matches on database?

Answer 4

• person moved abroad
• Interpol searches
• person may be in prison/hospital (prisoner swabbing programme 2003)
• mental health act
• person may not have re-offended
• person re-offending in a category of crime not routinely sampled by a force (however unlikely given approach of most forces since 2006)
• crime may not have been reported
• person may have died
• person may have never been caught

Question 5

What other tools may be used if there is no match on the database?

Answer 5

• familial searches
• Y STR
• rare allele mapping
• intelligence led screens
• FIGG (forensic investigative genetic genealogy

Question 6

What have studies shown family dispersion is correlated with?

Answer 6

• higher income
• higher education
• criminality runs in families
• offenders operate close to where they live or in an area with which they are familiar

(location of relative may lead to suspect)

Question 7

What case showcased familial searching?

Answer 7

• murders of three teenage girls in 1973 in South Wales
• in 2000, NDNAD searched for profiles of possible relatives to murderer
• gave < 100 names after filtered for South Wales
• DNA samples volunteered from relatives
• in 2000 - called operation magnum
• Joseph Kappen exhumed in 2002
• tooth and femur sampled and DNA match obtained

Question 8

Richard third DNA tests

Answer 8

• latest genetic tests have uncovered evidence of another royal sex scandal. - the indiscretion could potentially undermine the legitimacy of the entire House of Plantagenet.
• skeleton of Richard III, the last Plantagenet King, was discovered under a car park in Leicester in 2012
• his identity was confirmed through his mitochondrial DNA, passed down through the maternal line from his sister to two relatives alive today

Question 9

How is familial searching done?

Answer 9

• look for 2 types of relative using 2 different computer programmes
• parents of children of offender
• siblings of the offender

Question 10

How are siblings used for familial searching?

Answer 10

• siblings have same parents
• they inherit 50 % of their DNA from each parent
• siblings are likely to share more DNA with each other than with unrelated individuals who have inherited their DNA from a different set of parents

Question 11

What two things are used in familial searching?

Answer 11

• Y-STRs for males
• mitochondrial DNA for females

Question 12

How are Y-STR’s used in familial searching and screening?

Answer 12

• if a male appears on the familial lists as a possible parent, child or sibling of the offender, in order for that to be true, his Y-STR must match that of the crime scene stain
• if it does not, all his male siblings, together with his biological father and all his sons are eliminated as possible offenders

Question 13

How is mitochondrial DNA used in familial searching?

Answer 13

• If a female appears on the familial search results lists as a possible parent or sibling of the offender, in order for that to be true, her Mitochondrial DNA profile must match that of the crime scene stain.
• if it is does not match, all her siblings and her children are eliminated as possible offenders but her father is NOT eliminated in this situation

Question 14

What are the results from familial searching?

Answer 14

• two different computer programmes search entire NDNAD
• each will product a list of candidate profiles:
• parent/child list (profiles have at least one matching DNA band at each of the 17 loci
• sibling list (a list with number of matching DNA bands)
• lists may contain 1000s of individuals so need to be prioritised (discuss with police)

Question 15

How are likelihood ratios used in familial searching?

Answer 15

• it is a number that represents how likely an individual is to be related to offender
• calculated based on which alleles (as well as how many) the individual shares with the offender and how rare these are in the general population
• higher number = more likely the person is to be related
• a likelihood ratio allows ranking of both parent child and sibling results

Question 16

What are 5 case-specific parameters for the prioritisation of results list?

What can this info be used to do?

Answer 16

1 - ethnic appearance (witness statements, ethnic inference results)
2 - age (parameters around offender’s age)
3 - parent/child (must be at least 15 years older/younger)
4 - siblings (no more than 20 years older/younger)
5 - geography (‘relevant areas’ specific to case e.g. local, accents, exclusion of areas, major roads)

• re-prioritise as new information becomes available

Question 17

What is the latest on forensic investigative genetic genealogy in UK?

Answer 17

• recently genetics and genealogy have been combined to identify and prosecute high profile, serial rapists and murderers.
• the use of GEDMatch’s public database raise ethical concerns
  Nevertheless, some spectacular successes in the USA (link here)
  But how are these techniques applied?

Question 18

How do crime scene investigators collect samples from perpetrator?

Answer 18

• collect biological materials (blood, semen, hair or other cellular material)

Question 19

How will DNA degrade over time?

Answer 19

• under ideal conditions (-5 C) has 521 year half life
• will degrade quicker when exposed to heat, light, water and air

Question 20

How do users collect DNA samples using at home testing kit?

Answer 20

• e.g. 23 and Me, ancestry, my heritage
• spit into collection tube or swab cheek cells
• post to company
• 4 to 8 weeks get report generated online

Question 21

How is DNA tested in genotyping?

Answer 21

• DNA molecules are cut into fragments and added to genotyping chip
• the chips are covered in an array of 700k microscopic wells, each containing a probe that will match genetic variant which may or may not be present in DNA sample
• if the fragment matches, it can be labelled with one of the several fluorescent dyes that enables computer to read each associated DNA laser

Question 22

How is DNA testing done in genomics companies?

Answer 22

• genomic companies use different genotyping chips depending on what that company believes are the most informative genetic variants
• most companies allow users to download text file showing their genetic variants (genotypes)
• this is also loaded to GEDMatch, a searchable genealogy website

Question 23

What happens in searching database step?

Answer 23

• the DNA profile of genotypes for one person is compared against the profiles from the other GEDMatch’s public database

Question 24

What is each genotype?

Answer 24

• each genotype is a SNP (single nucleotide polymorphism - a single DNA letter) at one of the 700k positions that vary in human population
• the pattern and number of SNPs shared by any two people is used to calculate their genetic similarity

Question 25

What type of matches are often not returned on databases?

Answer 25

• not often high similarity matches
• only 50 % similar to parents
• 25 % similar to grandparents
• similarity decreases quickly
• for each generation (since cousins last shared a common ancestor) similarity is reduced by a quarter

Question 26

Why will you probably find tens or hundreds of third and fourth cousins?

Answer 26

• because there are enough profiles and their DNA is still similar enough to be identified by genetic similarity.

Question 27

How do genetic genealogists build a family tree?

Answer 27

• by applying traditional techniques to database info such as:
• names of two people
• DNA similarity
• census data
• newspaper obituaries
• birth and marriage certificates
• interviewing living relatives
• nowadays, research relationships via social media

Question 28

What happens once links between cousins are confirmed?

Answer 28

• genealogist will work backwards to find where the separate branches of a tree are connected at their (long dead) ancestors
• recent branches of the family tree (living relatives) are then added by building frameworks

Question 29

How are suspects found?

Give an example

Answer 29

• police agencies use conventional investigative methods before arresting a suspect.
• e.g. the Golden State killer, the investigators only had a list of third cousins (sharing great-great grandparents and under 1% genetic similarity) so, they had to use an extensive process of elimination
• in this case the offender was around 5’9” tall and around 75 kg for example to narrow down the list of suspects