Y-STR Analysis
Definition
Short tandem repeat profiling targeting the male-specific Y chromosome. Used when female victim DNA overwhelms the autosomal profile in a mixture, allowing isolation of the male contributor's genetic signature.
- Target
- Male-specific Y chromosome loci
- Key use case
- Isolating male contributor from female-dominant DNA mixtures
- Common scenario
- Sexual assault swabs with excess victim DNA
- Limitation
- Cannot individualise among paternal relatives
Common questions
Why is Y-STR analysis chosen over standard autosomal profiling in some sexual assault cases?+
When female victim DNA vastly outnumbers the male contributor's DNA in a mixture, the autosomal profile can be swamped by the majority contributor's alleles; Y-STR primers amplify only the Y chromosome, so male DNA is targeted directly regardless of how small a fraction of the sample it represents.
What is the main limitation of Y-STR evidence compared with autosomal STR evidence?+
All males in the same direct paternal line share the same or a very similar Y-STR haplotype, so a match indicates the donor belongs to a paternal lineage rather than pinpointing one individual, whereas autosomal STR profiles are essentially unique to an individual outside of identical twins.
Related terms
- Azoospermia
- The absence of spermatozoa from ejaculated semen, resulting from obstructive causes (vasectomy, ductal blockage) or non-obstructive causes (testicular failure). Azoospermic semen contains...
- Differential Extraction
- A two-step DNA extraction procedure used when a stain contains both sperm cells and non-sperm epithelial cells. The first step lyses epithelial...
- Double-Swab Technique
- A collection method for dried biological stains in which a moistened swab rehydrates and lifts the stain from the surface, followed immediately...
- Epithelial Cell Fraction
- The non-sperm cellular material in a sexual assault sample. Contains skin and mucosal cells from both victim and any perpetrator who made...
- Timing Window
- The period after an assault during which a specific locus is likely to yield viable foreign DNA. Windows vary substantially by locus:...