A forensic scientist performs DNA profiling using polymerase chain reaction (PCR) amplification of short tandem repeat (STR) loci from a degraded bone sample. The CODIS database in the USA uses 20 STR loci. In forensic DNA typing, which type of STR marker is specifically used for maternal lineage tracing because it is inherited exclusively maternally?

• A Autosomal STRs
• B Y-chromosomal STRs (Y-STRs)
• C X-chromosomal STRs (X-STRs)
• D Mitochondrial DNA (mtDNA) hypervariable regions ✓

Explanation

Mitochondrial DNA (mtDNA) is inherited exclusively through the maternal lineage (via oocyte cytoplasm) and is therefore used to trace maternal family relationships. It is also advantageous in degraded samples because each cell contains hundreds to thousands of mitochondria (high copy number), improving detection sensitivity from old or degraded bone. Y-STRs trace the paternal lineage through the Y chromosome. Autosomal STRs are used for individual identification and parentage testing. X-STRs provide additional power in kinship analysis involving sex-chromosome patterns.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

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Written and medically reviewed by the StethoPrep medical team.