Which DNA type is commonly used when nuclear DNA is unrecoverable due to degradation, and why?

Which DNA type is commonly used when nuclear DNA is unrecoverable due to degradation, and why?

• A. Chloroplast DNA; because it is plant-specific.
• B. Ribosomal RNA genes; because they are conserved.
• C. Mitochondrial DNA; because it is present in many copies per cell.
• D. Mitochondrial DNA; because it is present in many copies per cell and more likely recoverable from degraded samples.

Answer: (D)

The key idea is why copy number matters when DNA is degraded. Mitochondrial DNA is present in many copies per cell because each cell contains numerous mitochondria, each carrying multiple copies of the mitochondrial genome. When a sample is damaged and nuclear DNA is too fragmented or scarce to recover, those abundant mtDNA copies increase the chances that some intact template remains to be amplified by PCR. The mitochondrial genome is relatively small and yields short, amplifiable fragments, making it especially workable with degraded material. For these reasons, mitochondrial DNA is commonly used when nuclear DNA is unrecoverable due to degradation. (Chloroplast DNA is plant-specific and not helpful for human forensics, while ribosomal RNA genes are highly conserved and less useful for individual identification.)