Do Siblings Look Alike? The Genetics of Sibling Resemblance

Some siblings are dead ringers; others look like they belong to different families. Here's the genetic reason for the whole spectrum.

Why can one pair of siblings look like twins while another pair looks unrelated? It comes down to how genes are passed down — and it's the same reason every family photo is full of surprises.

Siblings share parents, not the same genes

Each child inherits a random half of each parent's genes, reshuffled independently every time. So while siblings share about 50% of their variable DNA on average, *which* 50% differs for each of them. Two siblings can draw very different combinations from the same gene pool — one favoring mom, one favoring dad, one favoring a grandparent.

Why some siblings look almost identical

By chance, two siblings can inherit similar combinations of the genes that shape the most visible features — nose, eyes, jaw — and end up looking strikingly alike. It's the same lottery, just landing on similar numbers. (Even identical twins drift apart over time thanks to environment.)

See it for yourself

Curious where you and your siblings land on the spectrum? The sibling resemblance test scores how alike your faces are — run each pairing and compare. Just remember it measures looks, not biology, as we cover in can a face tell you who a child looks like?.