Ask Lemmy
A Fediverse community for open-ended, thought provoking questions
Please don't post about US Politics. If you need to do this, try [email protected]
Rules: (interactive)
1) Be nice and; have fun
Doxxing, trolling, sealioning, racism, and toxicity are not welcomed in AskLemmy. Remember what your mother said: if you can't say something nice, don't say anything at all. In addition, the site-wide Lemmy.world terms of service also apply here. Please familiarize yourself with them
2) All posts must end with a '?'
This is sort of like Jeopardy. Please phrase all post titles in the form of a proper question ending with ?
3) No spam
Please do not flood the community with nonsense. Actual suspected spammers will be banned on site. No astroturfing.
4) NSFW is okay, within reason
Just remember to tag posts with either a content warning or a [NSFW] tag. Overtly sexual posts are not allowed, please direct them to either [email protected] or [email protected].
NSFW comments should be restricted to posts tagged [NSFW].
5) This is not a support community.
It is not a place for 'how do I?', type questions.
If you have any questions regarding the site itself or would like to report a community, please direct them to Lemmy.world Support or email [email protected]. For other questions check our partnered communities list, or use the search function.
Reminder: The terms of service apply here too.
Partnered Communities:
Logo design credit goes to: tubbadu
view the rest of the comments
23 and Me says my cousin is my sister...?
So, this is likely just the randomness of gene inheritance.
If we express cosanguinuity as percentages, you and your parent are at 50%, you and your grandparent 25%, etc. You get half your DNA from each parent, after all. But what about siblings? With siblings, you get into averages. You and your full sibling each got half your DNA from your mother and half from your father, but because the selection from each is random you could share anywhere from 0% to 100%. Rather than a flat 50%, you get a bell curve that peaks at 50%.
What if your sibling has a child with someone unrelated to you? Well, you and your niece or nephew are probably at about 25%, but because siblings are on a curve and there's a pair involved, you could be anywhere from 0% to 50%.
Similarly, first-cousins are typically about 12.5%, but 25% wouldn't be out of the realm of possibility and you could even get 50% if, say, their fathers are identical twins. If you and your cousin are simply on the upper end of the cosanguinuity bell curve, I could easily see one of those systems getting confused and thinking you're half-siblings, who would have a curve from 0% to 50% and peaking at 25%.
In short, testing just two random relatives doesn't actually tell you a lot unless you're testing a (supposed) ancestor and descendant. You would need to also get your parents and your cousin's parents tested to get anything definitive, and testing your grandparents too wouldn't be a bad idea for accuracy.
That also assumes any two unrelated people share 0% of their DNA. We all have common ancestors, if your uncle married a woman that happened to share 10% of your mom's DNA then you and your cousin could have more DNA in common as well.