Ever wonder how closely you’re related to someone based on your DNA? Think of DNA like a giant instruction manual that makes you you. You get half of it from your mom and half from your dad. So the more DNA you share with someone, the closer your biological connection.
But here’s the twist: you can share the same amount of DNA with different types of relatives—so scientists look at patterns, not just percentages, to figure out who’s who.
🔍 What the Percentages Mean
% Shared DNA Relationship Examples
100% Identical twins (you’re genetic clones!)
50% Full siblings (same mom and dad), or parent-child
~25% Half siblings (same mom or same dad), grandparents, aunts/uncles, nieces/nephews
~12.5–14% First cousins, great-grandparents, great-aunts/uncles
~6–7% First cousins once removed, half first cousins
~3–4% Second cousins
<1% Third cousins and beyond
👨👩👧👦 What About Half Siblings?
Half siblings share one biological parent—either the same mom or the same dad. That means they share about 25% of their DNA, not 50% like full siblings. But here’s the cool part: even though the percentage is lower, you can still have a super close bond. DNA doesn’t measure love—it just shows how the genes line up.
Also, if you and your half sibling share a dad, you’ll both have his Y chromosome (if you’re both male), or similar paternal DNA. If you share a mom, you’ll have more overlap in mitochondrial DNA, which comes from her.
🧩 Why It’s Not Always Obvious
Let’s say you share 25% of your DNA with someone. That could mean they’re your:
- Half sibling
- Aunt or uncle
- Niece or nephew
- Grandparent
So how do scientists figure it out? They look at:
• Which segments of DNA match
• Your ages and family tree
• Who else you’re both related to
It’s like solving a mystery with genetic clues!