FROM SAMPLE TO SNP PROFILE
Our work is completed in two phases, both involve direct genome sequencing. The purpose of Phase I is to evaluate the overall DNA quality of each sample. If the DNA quality is sufficient, we proceed to Phase II to develop the SNP profile.
Our Process
Figure: Astrea Forensics general laboratory workflow
Phase I: DNA Extraction, Sample Characterization via WGS, and QC report
The purpose of Phase I is to test each sample’s DNA preservation to determine the feasibility of providing a genome-wide SNP profile for genetic genealogy (Figure 2).
Our laboratory team extracts DNA and builds samples into next-generation sequencing (NGS) libraries. A NGS library is a sequence-ready work product compatible with all Illumina sequencers that has the added benefit of being able to amplify endlessly, effectively immortalizing your precious forensic sample.
The NGS libraries are lightly sequenced (~1 million sequence reads) to measure the amount of usable DNA present in each sample. Specifically, we learn what proportion of the DNA is human, how many of the human DNA fragments are unique, and more (see below). From this, we estimate the amount of sequencing necessary to achieve a high-quality genotype/SNP profile.
Phase I Deliverable
A summary QC report contains, whenever possible:
Sequencing metrics,
Sex estimate,
Mitochondrial lineage determination,
Complete mitochondrial genome sequence, if desired,
Comparison of nuclear DNA data between samples. Helpful for determining how many unique individuals are represented, or for ruling in/excluding known victims or other targets.
Recommendations and information for next steps.
Phase II Deliverable: Genotype File
For samples that pass QC, we generate hundreds of millions of DNA sequences. The goal is to reconstruct the entire autosomal genome. The Astrea Forensics pipeline uses the complete genome to impute the alleles at each target SNP position. We choose to report only SNPs that are helpful for comparing against direct-to-consumer genetic tests.
Phase II Deliverable
The resulting genotype is a text file containing between 1-2 million SNPs in a format suitable for upload to genetic genealogy databases.
Once the genotype file is delivered, we are committed to supporting law enforcement and forensic genetic genealogists until the case is solved.
Examples of how our technology is used to solve cold cases
