Familial DNA

When a human is conceived, they inherit half of their genetic material from their mother and half from their father. It is for this reason that most children resemble their parents in some feature and family traits are passed through the generations.

This means that children will always carry a 50% match to the DNA of each of their parents and, in the same way, the parents will be a 50% match for each of their children. This fact is used to resolve paternity disputes or identify bodies for which no DNA profile is available.

Every living cell in our body holds 46 chromosomes in 23 pairs. When we conceive a child we contribute a full chromosome from each pair and our partner does the same. This combination gives the child its full complement of 46 chromosomes. In identical twins, the resultant fertilised egg divides into two independent eggs, each carrying exactly the same genetic information.

The number of potential combinations for the offspring of two humans is 8,388,608.

Two children from the same parents may therefore possess none of the same chromosomes as a sibling. However in reality they usually share a significant amount and, in general, siblings from the same parents will be statistically more alike than the general poulation. This link may be enough, in serious cases, to give the police a valuable new line of enquiry by using a familial DNA search.

A Familial DNA search is a term used to describe a search of a crime scene stain on the national DNA database (NDNAD), not for the offender directly, but for the DNA profiles of people who may be their mother, father, a child or a sibling. These searches are restricted to the most serious offences, not only by virtue of cost, but also because of ethical implications.

Familial searching is compliant with the uses of the NDNAD specified by The Police and Criminal Evidence Act (PACE) or the Police Powers and Procedures Act (PPP) on the Isle of Man. It is strictly regulated by the Association of Chief Police Officers (ACPO) and only performed after rigorous consultation. A familial search would never be performed until the crime scene DNA had been speculatively searched on the DNA database, and no match made.

The Data Protection Act says that it would only be proportionate if restricted to the most serious of cases. It recommends that all reasonable steps should be taken to minimise intrusion into the private lives of individuals. The reason underlying this is that you are searching for individuals who have not, themselves, committed the crime and therefore the intrusion into their privacy should be proportionate to the offence being investigated.

The National DNA Database (NDNAD) now holds nearly three million DNA profiles from individuals who have been cautioned, charged or convicted of a criminal offence. The database also holds the profiles of DNA which has been recovered from crime scenes.

Familial searches examine the entire NDNAD, but are initially restricted to Second Generation Mulitiplex (plus) SGM+ profiles. DNA profiles contain information about a number of regions of DNA that are variable in humans and differ between individuals. These regions are called loci. Each locus is characterised by two peaks or bands, which are known as alleles. SGM+ profiles contain information about ten variable regions (loci) of DNA and have a sex marker.

The initial searches produce two lists of potential profiles. One list contains the names and demographics of potential children and parents of the offender and the other list contains the same information about potential siblings. As the initial searches have only considered genetic information about the individuals held on the NDNAD, the result lists could potentially contain a substantial number of profiles, dependent on the frequency with which the bands occur in the general population. In order to further prioritise these lists, criteria such as ethnicity, age and geographic location are applied to the results thereby reducing the lists considerably.

Ethnicity - Information may be obtained from witnesses or from ethnic inference testing.

Age - Information on the offender’s age can be used to exclude individuals on the lists. For example, individuals born less than 15 years before the offender are unlikely to be their parents, and likewise individuals born less then 15 years after the offender are unlikely to be their children. Siblings of the offender are unlikely to have been born more than 20 years before or after the offender.

Geography - Geographic information can be utilised in a number of ways to prioritise the information on the results lists. The following generally accepted broad assumptions are made:

• Families at the lower end of the socio-economic scale are less likely to disperse than those at the higher end.
• Criminality runs in families.
• Criminals tend to offend in areas with which they are familiar.

Using these assumptions the postulation is that the offender will often have committed a crime in their local area or that the area immediately surrounding the crime scene is of considerable relevance.

These assumptions indicate that it is also likely that the offender’s family members live in the area and may have committed crime there themselves resulting in their DNA profiles being loaded onto the NDNAD. If a familial match is made near to the crime scene it is therefore likely that the offender is also still resident in the area.

Relevant geographical areas may also be identified by considering the accent of the offender or other circumstances relating to the crime. Similarly, areas may be excluded if they are thought for some reason to have no association with the crime.

Ultimately, these techniques are used to target individuals who are a significant risk to our society, or to detect serious crime. If a person can be located, arrested and safely convicted using familial DNA searching we can hopefully prevent them from committing serial offences.

OPERATION ANCESTRAL

Currently, in the Isle of Man, we have one case which is the subject of a familial DNA search: In August 1989 the body of a newborn baby was discovered in a bath at Noble's Hospital nurses home. The baby had died as a result of being left in the bath and not cared for.

Extensive enquiries failed to trace the mother or father of the baby, which was laid to rest in Douglas cemetery.

Advances in DNA technology have allowed us to obtain the DNA profile of the child and perform a speculative familial search of the DNA database. This process is still current and provides us with the best method of locating the parents of the child, unless they wish to contact us directly to explain what happened all those years ago.

We are appealing for his parents (or anyone with information that could lead to the identification of any persons concerned with his birth, short life and subsequent death) to contact us.

Messages can be left on a dedicated Operation Ancestral message line 01624 631275 or emailed to ancestral.dha@gov.im. Alternatively, any person able to assist the inquiry can contact Police Headquarters on 01624 631212 or use the confidential Crimestoppers line on 0800 555 111.