The number of fragments mapping to each position in the genome — the coverage — determines how reliably that position can be characterized.

Positions covered by many independent reads are characterized reliably; positions covered by few reads are characterized with more uncertainty.

For the Trail Creek tooth, the researchers achieved enough coverage to make meaningful inferences about the child’s population ancestry, sex, and mitochondrial lineage.

The specific coverage levels achieved are not always reported in detail in the primary literature, but the conclusions drawn are calibrated to what the available coverage supports — with appropriate acknowledgment that higher coverage would have allowed more precise characterization of the child’s ancestry and genetic relationships.

The sex determination — identifying the child as female — used the specific approach of comparing coverage on the sex chromosomes (X and Y) to coverage on the autosomes (the non-sex chromosomes).