Ancestry DNA redux: Bantu, centimorgan

The very day I posted my DNA results from Ancestry.com back in September, I got this:
“We’re always working to improve our DNA science and with more than 150 new regions, we’ve brought even more detail to your results.”

“This update may connect you to additional new regions or migration stories. It’s also possible that some of your previous regions have disappeared, as our data has become more precise. Either way, it’s an update that gives you a clearer picture of your origins than ever before.” They say my DNA hasn’t changed, but their understanding does. Compare with the last one:

So I’m part southern Bantu, which didn’t show up at all the first go round. I’m more from Benin/Togo. I’m more from Great Britain/Ireland, and there’s a potential familial lead in Munster, Ireland.

But I’m less Scandinavian, and less Nigerian. My Native American went from less than 1% to 1%, not exactly a telling statistic.

Meanwhile, they’ve added some additional information to the familial field. There’s some woman they’ve identified as my potential 2nd or 3rd cousin. “Shared DNA: 302 cM across 14 segments”. What the heck is a cM?

“In genetics, a centimorgan (abbreviated cM) or map unit (m.u.) is a unit for measuring genetic linkage. It is defined as the distance between chromosome positions (also termed loci or markers) for which the expected average number of intervening chromosomal crossovers in a single generation is 0.01. It is often used to infer distance along a chromosome. However, it is not a true physical distance.”

Got it. OK, don’t “got it.” What? BTW, the person I know IRL who is my second cousin- Shared DNA: 250 cM across 17 segments. Lillian Bell Archer, is our common ancestor, our great-grandmother. Lillian is my mother’s mother’s mother.

As my cousin once said, “This is addicting stuff.” Will I share my DNA with greatness?