Which best describes the role of Y-chromosome STRs in sexual assault investigations?

• A. Assist in identifying female DNA when male DNA is the minor contributor.
• B. Assist in detecting male DNA when female DNA is the major contributor and help link the male to the evidence.
• C. Replace autosomal STR analysis entirely.
• D. Used to determine the age of DNA.

Answer: (B)

Y-chromosome STRs are male-specific markers that are especially useful when the DNA from a male contributor is overwhelmed by female DNA in a sample. In sexual assault cases, the evidence often contains predominantly female DNA with only trace amounts of male DNA. Analyzing Y-STRs focuses on loci on the Y chromosome, so it can reveal the presence of male DNA that autosomal STR analysis might miss in mixed samples. This allows investigators to detect a male contributor and to link that male’s DNA across multiple pieces of evidence by comparing the Y-STR haplotype, helping relate evidence items to the same male donor.

This approach does not replace autosomal STR analysis, which provides a more detailed and individualized profile. Y-STR data also cannot uniquely identify a person in most situations since many males can share similar Y-STR haplotypes, and it cannot be used to determine the age of DNA.