Mitochondria, the energy-producing structures in cells, have their own separate, small genome, inherited exclusively through the maternal line.

When the researchers sequenced Denny’s mitochondrial DNA, it matched Neanderthal sequences — specifically, sequences found in Neanderthal populations from western Eurasia.

This confirmed that Denny’s mother was a Neanderthal.

The third line was analysis of the nuclear DNA in more detail.

The nuclear genome consists of pairs of chromosomes, with one copy of each chromosome inherited from the mother and one from the father.

By looking at the specific genetic variants on the maternal and paternal copies of Denny’s chromosomes, researchers could determine which variants came from which parent.