Because ancient DNA is highly fragmented, this approach is well-suited to the material — rather than trying to sequence long intact molecules, the sequencer reads many short pieces and computational methods are then used to assemble them into a coherent picture by comparison with reference genomes.

One of the key metrics for ancient-genome work is coverage — the average number of times each position in the genome is represented by sequenced reads.

Higher coverage means more information and more reliable conclusions.

For a sample as small and as old as the Trail Creek tooth, achieving high coverage across the full genome is exceptionally challenging.

The amount of ancient DNA in a single small tooth is limited, and the fragmentation and damage that characterize ancient specimens mean that not every read can be reliably mapped to the reference genome.

Despite these challenges, the researchers extracted sufficient genetic material from the Trail Creek tooth to make meaningful conclusions about the child’s ancestry.