Match differences

[Norfolk Nan]

Just wondered if anyone else had noticed differences in the number of cMs in some matches when an original test is uploaded to a second site?

I uploaded my Ancestry DNA test to MyHeritage and received another list of matches. Obviously some matches are on both sites but a few have significant discrepancies- one as much as a third less on the original Ancestry test. I’m sure there’s a good technical reason … can anyone explain?

[AdrianBruce]

Without plunging into reference material that I barely understood the first time round, I think that the answer that the matching process is a lot more complicated than just counting "the votes from the Norwegian Jury".... (Old TV phrase if it means nothing to you...) Each site has different algorithms for what - or perhaps where is a better word? - gets counted. Hence one site may count up 32 cM, another 48 cM.

Contradictions welcome!

[Norfolk Nan]

Ah, that explains it: algorithms! And I thought it was a precise science… silly me!

[AdrianBruce]

If I recall correctly, I recently read that it's easy to get the wrong idea about the DNA differences between 2 human beans - you end up thinking that there is virtually nothing in common between you and your tenth cousin - but since so many bits of DNA do basically the same thing across all plants and animals, there's actually massive commonality across all living things - a simplistic view, for instance, says that we share 50% of our DNA with a banana. So DNA comparisons have to look in specific places and ignore the bits liable to be identical between all of us.