How can sex be identified using STRs?

How can sex be identified using STRs?

• A. By analyzing the amelogenin gene, which is shorter by 6 bases on the X chromosome than on the Y chromosome.
• B. By measuring total DNA concentration.
• C. By analyzing mitochondrial DNA length.
• D. By the presence of a single STR marker on the Y chromosome only.

Answer: (B)

Sex identification with STRs hinges on differences between the X and Y chromosome sequences that STR analysis can reveal. The most commonly used example is the amelogenin gene, where the X and Y copies yield differently sized PCR products. In a male, both copies are present, giving two distinct fragments (one from the X and one from the Y), typically separated by about six base pairs. In a female, only the X copy is present, so you observe a single fragment size. This size difference is detectable with standard STR sizing methods and provides a robust way to infer sex from DNA. Measuring total DNA concentration doesn’t indicate sex because it merely reflects how much DNA is present, not which chromosome it comes from. Mitochondrial DNA length isn’t informative for sex since mtDNA is inherited maternally and isn’t linked to the sex chromosomes. While a Y-chromosome STR marker can point to male DNA, relying on a single Y-STR marker isn’t as reliable for sex determination as using a locus like amelogenin (often complemented by a panel of other markers) because of potential issues like mixtures, degradation, or marker dropout.

Sex identification with STRs hinges on differences between the X and Y chromosome sequences that STR analysis can reveal. The most commonly used example is the amelogenin gene, where the X and Y copies yield differently sized PCR products. In a male, both copies are present, giving two distinct fragments (one from the X and one from the Y), typically separated by about six base pairs. In a female, only the X copy is present, so you observe a single fragment size. This size difference is detectable with standard STR sizing methods and provides a robust way to infer sex from DNA.

Measuring total DNA concentration doesn’t indicate sex because it merely reflects how much DNA is present, not which chromosome it comes from. Mitochondrial DNA length isn’t informative for sex since mtDNA is inherited maternally and isn’t linked to the sex chromosomes. While a Y-chromosome STR marker can point to male DNA, relying on a single Y-STR marker isn’t as reliable for sex determination as using a locus like amelogenin (often complemented by a panel of other markers) because of potential issues like mixtures, degradation, or marker dropout.