Which statement best describes 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 are not informative for determining gender.
• 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 used for non-human DNA analysis.

Answer: (C)

Y-STRs are short tandem repeats on the Y chromosome, which is present only in males. Because a male has a single copy of the Y chromosome, each Y-STR locus is effectively haploid, so you observe only one allele (one peak) at each locus. This single-peak pattern is what makes Y-STR typing particularly useful when a DNA mixture contains female DNA—the female contributor cannot contribute a Y chromosome, so any Y-STR signal must come from a male. That lets you identify or confirm the presence of a male contributor even in a mixed sample. At the same time, Y-STRs have limitations: they cannot distinguish between different male relatives who share the same Y-haplotype, and they are not informative for analyzing non-human DNA.