What is the significance of Y-STRs in forensic DNA analysis?

• A. Y-STRs are useful for analyzing DNA from female mixtures, as they show only one peak for each STR type.
• B. Y-STRs show no peaks for any STR type.
• C. Y-STRs are useful for analyzing DNA from male mixtures, as they show only one peak for each STR type.
• D. Y-STRs are not helpful in forensic DNA analysis.

Answer: (C)

Y-STRs are markers on the Y chromosome and are inherited from father to son, so a male’s DNA shows a single allele at each Y-STR locus. In a mixed DNA sample that includes female DNA, the female cannot contribute Y-STR signals, so the peaks observed at Y-STR loci come from the male contributor. Because the Y chromosome is effectively haploid in males, each Y-STR locus appears as a single peak, making these markers particularly informative for detecting and characterizing male DNA in mixtures. This is why Y-STRs are useful for analyzing DNA from male mixtures. They aren’t useful for analyzing female mixtures (no Y chromosome), and they do produce peaks, just one per locus.