When nuclear DNA is unrecoverable, which type of DNA is commonly used and why?

When nuclear DNA is unrecoverable, which type of DNA is commonly used and why?

• A. Chloroplast DNA, because it is present in plant cells.
• B. Ribosomal RNA genes, because they are conserved.
• C. Mitochondrial DNA, because it is present in many copies per cell and more likely recoverable from degraded samples.
• D. Y-chromosome DNA, because it is easier to amplify.

Answer: (C)

When nuclear DNA cannot be recovered, mitochondrial DNA is used because mitochondria exist in many copies per cell, dramatically increasing the amount of DNA you can extract from degraded material. This high copy number makes mtDNA more likely to yield usable sequences from old bones, hair shafts without roots, or other badly preserved samples. The mitochondrial genome is a small circular molecule inherited maternally, and its analysis typically targets short regions that survive in fragments, which is ideal when the DNA is compromised. A key trade-off is that mtDNA is not unique to an individual; it is shared along maternal lines, so it provides information about maternal ancestry rather than a unique identity. That’s why mtDNA is valuable for identification in cases where nuclear DNA is unavailable, but it can’t distinguish between close maternal relatives the way autosomal nuclear DNA can. Chloroplast DNA is specific to plants, so it isn’t applicable for human remains. Ribosomal RNA genes are highly conserved, which makes them less informative for individual identification. Y-chromosome DNA is nuclear and useful in certain contexts (like aiding in male-specific profiling or mixture analyses), but it does not address the issue of degraded nuclear DNA as effectively as mtDNA and has its own limitations.

When nuclear DNA cannot be recovered, mitochondrial DNA is used because mitochondria exist in many copies per cell, dramatically increasing the amount of DNA you can extract from degraded material. This high copy number makes mtDNA more likely to yield usable sequences from old bones, hair shafts without roots, or other badly preserved samples. The mitochondrial genome is a small circular molecule inherited maternally, and its analysis typically targets short regions that survive in fragments, which is ideal when the DNA is compromised.

A key trade-off is that mtDNA is not unique to an individual; it is shared along maternal lines, so it provides information about maternal ancestry rather than a unique identity. That’s why mtDNA is valuable for identification in cases where nuclear DNA is unavailable, but it can’t distinguish between close maternal relatives the way autosomal nuclear DNA can.

Chloroplast DNA is specific to plants, so it isn’t applicable for human remains. Ribosomal RNA genes are highly conserved, which makes them less informative for individual identification. Y-chromosome DNA is nuclear and useful in certain contexts (like aiding in male-specific profiling or mixture analyses), but it does not address the issue of degraded nuclear DNA as effectively as mtDNA and has its own limitations.