Genealogy question (DNA matching)

[target2019]

Even though we know for a fact we are 2nd cousins once removed, we share over 600 cM, which seems like a lot.

According to the chart posted, you're shared number is high. You can download autosomal results and upload to other sites: FTDNA, Gedmatch, MyHeritage. You might see other reasons in trees that confirm the number or suggest reasons why.

 

[Montecfo]

It's a girl!

Found out last year I have a sister (same father) 7 years younger that no one knew about. And 3 nieces!
This was through ancestry.com.

I was delighted and so was my brother. My half-brother (same father) denies it all and refuses to consider it. Our father passed away years ago. To me there is no scandal, just bigger family.

These are hard issues for people!

 

[Winemaker]

These DNA tests only show your maternal DNA links, you will not get any paternal DNA. That means, your test will show only your 6th great grandfather's MOTHER's DNA. If you are female, you will NOT have any Y chromosomes, the carrier of male genes. If your father was tested, you may be able to examine and compare the same DNA contribution. Your 6th great grandfather's DNA would only show up in your DNA, if there was a straight male to male link each generation from him to your father.



"My 6th great-grandfather was Cherokee, but after dilution, very few in my generation would register much if any NA blood."

 

[braumeister]

I believe I have the answer

Well, I dug into it some more and used some different genealogy software, and I think I found the problem.

Whereas we were sure we were second cousins, it turns out that technically (according to the software) we are first cousins once removed. So the high DNA match is reasonable.

What we learned is that there was a mixup among names in the past, and once we got that sorted out we found the issue. Her grandparents were half cousins, since they shared one grandparent (not two as would normally be the case). Based on what we know about the circumstances back then, it's likely they didn't know they were related, which explains it.

Anyway, thanks for all the advice!