Mitochondrial and Y-STR DNA
When nuclear DNA is insufficient—hair shafts without roots, ancient skeletal remains, highly degraded samples—mitochondrial DNA (mtDNA) analysis offers an alternative. Each cell contains hundreds of mitochondria, each with multiple copies of a 16,569 base-pair circular genome, providing far more template copies than nuclear DNA. The hypervariable regions (HV1 and HV2) are sequenced and compared. However, mtDNA is maternally inherited and shared by all maternal relatives, so it cannot uniquely identify an individual—it can only exclude or fail to exclude. Y-chromosome STR (Y-STR) analysis targets the male-specific Y chromosome, useful in sexual assault cases where male DNA must be distinguished from an overwhelming female DNA background. Like mtDNA, Y-STRs are inherited without recombination and shared by all paternal relatives.