Complex sentence: Aunts are second-degree relatives and share 25% genetic overlap when they are the full sister of the parent and is a third-degree relative with 12.5% genetic overlap.
Split into simpler sentences: Aunts are second-degree relatives and share 25% genetic overlap when they are the full sister of the parent. A half-aunt is a half-sister of one's parent and is a third-degree relative with 12.5% genetic overlap.