Female individuals have two X chromosomes and no Y, so all sequenced reads from sex chromosomes map to the X; male individuals have one X and one Y, so reads map to both.

The ratio of X to Y coverage is a reliable indicator of genetic sex, and for the Trail Creek sample, the pattern was consistent with female sex.

The population ancestry assignment — placing the child within the Ancient Beringian group — used genome-wide patterns of allele frequencies to determine which reference populations the Trail Creek genome clustered with in statistical analyses.

The same types of analyses that revealed USR1’s Ancient Beringian ancestry, when applied to the Trail Creek data, placed the Trail Creek child in the same cluster — indicating that both individuals shared the specific genetic profile that characterizes the Ancient Beringian branch.

The Limestone Ridges and the Life Above the Lake