Identity by descent (IBD) describes a DNA segment that two people have inherited from a common ancestor—a concept that provides the framework for FGG work. Two samples sharing overlapping segments across chromosomes allows genealogists to approximate the degree of kinship, with recombination events helping distinguish whether DNA is inherited or shared by chance (Figure 2). The length of an IBD segment is measured in centimorgans (cM), which measure genetic distance. The larger the cM value, the more DNA is shared between two people and the more likely they are to be related (Table 1).

Figure 2: IBD segment lengths approximate the amount of shared DNA between two samples. GEDmatch converts the SNP calls (A, G, C, or T) from a DTC genetic test into IBD segments.²

Where permitted, forensic databases already enable short-range familial searches to find close relatives. However, they use only a small number of markers and restrict the pool of DNA profiles to people who have come into contact with law enforcement. When a forensic database fails to produce a hit, a genealogical database can broaden the search by increasing the DNA profile pool and expanding the search criteria.

GEDmatch is the only genealogical database that aggregates DNA profiles from all DTC genetic testing companies—an approach that allows it to compare data from unknown samples against a diverse and extensive set of volunteer data. A long-range familial search finds distant relatives or sets of relatives within this extended data set. The results yield a simple measure of kinship based on IBD segments that can, for example, identify second cousins of a sample contributor.³

Figure 3 illustrates an example GEDmatch query result with graphical representation of two shared segments on human chromosome 6. For each of the two segments, the table shows start and end locations on the chromosome, total length in centimorgans, and the number of shared SNPs. SNP allele calls, which are not necessary for FGG, are excluded from GEDmatch results.

Figure 3: An association between two people on a segment of chromosome 6. The horizontal dark green bars indicate two shared segments, while the table displays information about each segment.

Although the GEDmatch database is a powerful tool, the large-scale SNP array methods that generate the data it contains are incompatible with the challenging samples typical in forensic casework. Verogen leverages GEDmatch data to identify an optimum set of compatible markers to combine in a dense NGS SNP assay designed for low- quantity, low-quality samples. The amplicons are small—ideal for degraded DNA—and selected to be the most informative. Sequencing these amplicons on the MiSeq FGx® Sequencing System targets the data relevant to FGG. In turn, GEDmatch uses only the critical markers to find relatives. The Verogen NGS workflow ultimately requires less sample than traditional methods and limits data to the specific set needed for FGG.

FGG plays a growing role in correcting miscarriages of justice and identifying violent offenders who evaded detection. After decades of dead ends, GEDmatch assisted with the identification of Joseph James DeAngelo as the alleged Golden State Killer. His arrest in April 2018 cast a spotlight on FGG, highlighting its potential as a mainstream forensic tool.

In June 2019, the conviction of William Earl Talbott II for the 1987 murder of a young Canadian couple, Tanya Van Cuylenborg and Jay Cook, marked the first-ever guilty verdict for a case that relied on FGG evidence. Data from DNA collected at the crime scene over 30 years ago were uploaded to GEDmatch, helping identify Talbott after decades of anonymity. ⁴

In another cold case, FGG helped to not only identify the offender, but release the man wrongly convicted of the crime. Unsatisfied with the conviction of Christopher Tapp of the 1996 rape and murder of her daughter, Angie Dodge, Carol Dodge pushed for a proper resolution of the case. Fraught with inconsistencies, the original case included an alleged coerced confession that Tapp later recanted and a lack of direct evidence. Critically, none of the crime-scene DNA matched Tapp.

In May 2019, an FGG breakthrough led to the arrest of Brian Leigh Dripps and the definitive clearing of Tapp. A DNA sample from the crime scene was processed and compared with profiles in GEDmatch, identifying Dripps as a possible suspect. Investigators then obtained a discarded cigarette butt for comparison to hair and semen samples from the 1996 crime scene, which matched. When questioned, Dripps admitted to the crime.⁵

Without an identification, cases can languish for decades, suspending survivors, families, and the wrongly convicted in a state of uncertainty while offenders go free. The ability of Verogen NGS technology to advance challenging samples, limit data exposure, and find relatives through shared DNA unlocks an opportunity to push genealogy further. FGG has already demonstrated the capability to generate investigative intelligence that can identify the anonymous and reanimate cold cases.

Working in concert with the forensic community, Verogen is leveraging the MiSeq FGx System and GEDmatch to develop FGG as an end-to- end, fully integrated solution. Based on gold-standard NGS technology, the solution integrates instrument, chemistry, analysis software, and database—backed by evaluation and implementation services—to equip forensic laboratories with more ways to generate investigative intelligence from DNA. As the only portfolio to include this capability, Verogen is uniquely able to bring the next era of genealogy into your laboratory.

To learn more about the GEDmatch database, visit: www.verogen.com/a-message-to-verogen-customers-about-the- gedmatch-partnership

To learn more about the MiSeq FGx System, visit: www.verogen.com/miseq-fgx/

1. Callaghan, Thomas F. 2019. “Responsible genetic genealogy.” Science 366(6462):115. doi:10.1126/science.aaz6578.
2. Greytak, Ellen M., CeCe Moore, Steven L. Armentrout. Genetic genealogy for cold case and active investigations. Forensic Science International. 2019;299:103–113. https://doi.org/10.1016/j. forsciint.2019.03.039
3. Erlich, Yaniv, Tal Shor, Istik Pe’er, Shai Carmi. 2018. “Identity inference of genomic data using long-range familial searches.” Science 362(6415):690–694. doi:10.1126/science.aau4832.
4. Murphy, Heather. 2019. “Genealogy Sites Have Helped Identify Suspects. Now They’ve Helped Convict One.” New York Times, July 1. https://www.nytimes.com/2019/07/01/us/dna-genetic- genealogy-trial.html.
5. Bishop, Shane. 2019. “Police arrest Idaho man in 23-year-old cold- case murder of Angie Dodge.” NBC News, May 16. https://www. nbcnews.com/dateline/police-arrest-idaho-man-23-year-old-cold- case-murder-n1006726.