Mind-blowing Forensic Genetics

In the early hours of 4 Feb 2012, Troy and LaDonna French were gunned down in their home in Reidsville, NC. The couple awoke to screams from their 19-year old daughter, Whitley, who had detected the presence of a male intruder in her second floor room. As they rushed from their downstairs bedroom to aid their daughter, the intruder attempted to quiet the girl with threats at knifepoint. Failing this, he released Whitley and raced down the stairs. After swapping his knife for the handgun in his pocket, he opened fire on the couple as they approached the stairwell. During his escape, the perpetrator left a few drops of his blood on the handrail, apparently the result of mishandling his knife. DNA from this bloodstain would later prove crucial in enabling the Rockingham County Sheriff’s Office (RCSO) to solve the case. In Feb 2015, after reading about the recent debut of the Parabon Snapshot® DNA Phenotyping Service, Captain Howell contacted Parabon to explore the possibility of obtaining phenotyping analysis of the perpetrator’s DNA. By April, samples were delivered to AKESOgen, one of the genotyping labs that supports Parabon’s unique brand of DNA analysis. Unlike traditional DNA crime labs, AKESOgen performs genotyping of single-nucleotide polymorphisms (SNPs, pronounced “snips“), the millions of markers on the genome that collectively encode the genetic information that accounts for much of the trait differences in people. Starting with 30 ng of DNA, AKESOgen used the Illumina CytoSNP-850K chip to genotype over 850,000 SNPs from the sample, with an overall call rate of 98.9%. With the resulting SNP genotype data, Parabon scientists used Snapshot to predict the perpetrator’s likely appearance and ancestry. Snapshot® Composite Profile for Case #3999837068, Rockingham County, NC Sheriff’s Office A comparison of the Snapshot Composite Profile and a photo of José Alvarez, Jr. taken at the time of his arrest. On 7 May 2015, Parabon briefed Captain Howell and Detective Marcus Marshall, lead investigator on the case, about the Snapshot results for their sample. The subject’s DNA indicated he had fair or very fair skin, brown or hazel eyes, dark hair, and little evidence of freckling. Face morphology analysis suggested the subject had a wide facial structure and non-protruding nose and chin. Importantly, Snapshot analysis indicated the subject had admixed ancestry, a roughly 50-50 combination of European and Latino ancestry consistent with that observed in individuals with one European and one Latino parent. John Alvarez has such admixed ancestry, but DNA analysis had ruled him out as a suspect, and Y-STR analysis indicated the perpetrator did not share a paternal lineage with John. Nevertheless, the Snapshot predictions for the case were highly consistent with John’s brother, José Alvarez Jr. “The Snapshot ancestry analysis and phenotype predictions suggested we should not eliminate José as a suspect, despite the Y-STR results,“ said Detective Marshall. “The likeness of the Snapshot composite with his driver’s license photograph is quite striking.“ Within weeks of receiving the Snapshot report, Detective Marshall requested a DNA sample from José Alvarez Jr., and his father José Alvarez Sr. Both consented to be swabbed. Traditional DNA analysis proved beyond all doubt that the blood on the stairwell in the French home had come from José Alvarez Jr. It also showed, to everyone’s surprise, that José Alvarez Sr. is not his biological father, which is why the Y-STRs did not match.