Investigative genetic genealogy (IGG) has emerged as a new, rapidly growing field of forensic science. We describe the process whereby dense SNP data, commonly comprising more than half a million markers, are employed to infer distant relationships. By distant we refer to degrees of relatedness exceeding that of first cousins. We review how methods of relationship matching and SNP analysis on an enlarged scale are used in a forensic setting to identify a suspect in a criminal investigation or a missing person. There is currently a strong need in forensic genetics not only to understand the underlying models to infer relatedness but also to fully explore the DNA technologies and data used in IGG. This review brings together many of the topics and examines their effectiveness and operational limits, while suggesting future directions for their forensic validation. We further investigated the methods used by the major direct-to-consumer (DTC) genetic ancestry testing companies as well as submitting a questionnaire where providers of forensic genetic genealogy summarized their operation/ services. Although most of the DTC market, and genetic genealogy in general, has undisclosed, proprietary algorithms we review the current knowledge where information has been discussed and published more openly.

Thousands of people worldwide have been conceived using donor gametes, but not all parents tell their children of their origin. Several countries now allow donor-conceived offspring to potentially know their genetic parent if they are informed of their donor-conceived status. At the same time, personal genetic testing is a rapidly expanding field. Over 3 million people have already used direct-to-consumer genetic testing to find information about their ancestry, and many are participating in international genetic genealogy databases that will match them with relatives. The increased prevalence of these technologies poses numerous challenges to the current practice of gamete donation. (i) Whether they are donating in a country that practices anonymous donation or not, donors should be informed that their anonymity is not guaranteed, as they may be traced if their DNA, or that of a relative, is added to a database. (ii) Donor-conceived adults who have not been informed of their status may find out that they are donor-conceived. (iii) Parents using donor conception need to be fully informed that their children's DNA will identify that they are not the biological parents and they should be encouraged to disclose the use of donor gametes to their children. Together, these concerns make urgent a wide-ranging societal conversation about how to best safeguard and promote the interests of donor-conceived offspring and protect the rights of donors. Specifically, there is a need to ensure that new genetic information is communicated in a way that promotes both the safety and the privacy rights of offspring and donors alike. All parties concerned must be aware that, in 2016, donor anonymity does not exist.

Highlights • Genetic genealogy databases produce investigative leads in cold and active cases. • Many people in the databases have not given informed consent for law enforcement use. • There is an unknown number of minors in the databases. • You are affected if you have a relative in the databases even if you have not tested. • International interdisciplinary best practice guidelines are needed.

The use of genetic genealogy techniques to identify Joseph James DeAngelo as the prime suspect in the Golden State Killer case in 2018 has opened up a new approach to investigation of cold cases. Since that breakthrough, genetic genealogy methods have been reported to be applied to around 100 cases. To date, all of these reports relate to investigations in the US, where the high uptake of "direct-to-consumer" (DTC) genetic testing by individuals conducting private ancestral research has provided the necessary publicly available data for successful forensic investigations. We have conducted a study to assess the likely effectiveness of genetic genealogy techniques if applied to investigations in the UK. Ten volunteers provided their own SNP array data, downloaded from a DTC provider of their choice. These data sets were anonymised and uploaded to the GEDmatch Genesis genealogy website, mimicking data sets from unsourced crime samples or unidentified human remains. A team of experienced genealogists then attempted to identify the donors of the anonymised data sets by working with matches on the database and identifying points where the matches' trees intersect to determine their shared family lineages which were further investigated using traditional resources (such as birth, marriage, death and census records, social media and online family trees). Through these methods, four of the ten donors were identified, at least to the level of one of a set of siblings. This confirms that, despite the over-representation of US citizens on publicly accessible genealogy databases, there is still potential for effective use in investigations outside the US where legislation permits. One of our four identified individuals was of Indian heritage (via St Vincent and the Grenadines) highlighting that in the right circumstances individuals of non-European origin can be identified.

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