Average shared centiMorgans with MRCA in the early 1700s?

[NicVog]

Hey, everyone. So far the people of Rootschat have been very kind and helpful as I work on figuring out my grandmother's family tree.

I had found via DNA testing a few branches of a family I believe she descended from, but can't be sure. One of these distant relatives I mistakenly thought belonged to a closer branch of the family than he actually did, but as it turns out, he belongs to a branch of the Goforth family that the shared ancestor of he and (possibly) my great uncle and grandmother, lived in the late 1600s and died in the 1720s. His shared DNA was 45 cM over a single segment, but I wonder if that's excessively large for an ancestor living so early.

There are other branches of the same family, with shared ancestry from the late 17-early/mid 1800s we found some common matches with, from the late 20s-mid teens range over a single segment, which maybe sounds a little more likely, but I wondered what's the average, and maybe the highest shared cM you've seen with a relative from two or three centuries back?

https://www.rootschat.com/forum/index.php?topic=821670.msg6843813#msg6843813

[Rosinish]

I don't have enough knowledge/experience etc. but my brother has done his DNA & for a 3rd - 6th cousin with 1 segment it's 61%.

I have no idea what era this would be for & my brother has no interest in genealogy/tree etc.

Annie

Add...I had a look & it's 3 x g which is c1770 although I have no idea which line going back?

It's 23andme i.e. no trees but I find the family names are more recent (a couple of generations) i.e. no way of knowing.

[SelDen]

Scroll down in this link to get to the table on page 4:
https://thegeneticgenealogist.com/wp-content/uploads/2017/08/Shared_cM_Project_2017

[sugarfizzle]

Scroll down in this link to get to the table on page 4:
https://thegeneticgenealogist.com/wp-content/uploads/2017/08/Shared_cM_Project_2017

The 2 links below are both for the shared cM project referred to, DNA painter is an interactive version, much used by regulars to this board.

Shared cM project 2017 (original)
https://thegeneticgenealogist.com/2017/08/26/august-2017-update-to-the-shared-cm-project/

Shared cM estimate tool (DNA Painter)
https://dnapainter.com/tools/sharedcmv4

Regards Margaret

[sugarfizzle]

I wondered what's the average, and maybe the highest shared cM you've seen with a relative from two or three centuries back?

MRCA 3G grandparents, born c 1800, 4 matches share 55 cMs across 6, 47 cMs across 3, 28 cMs across 1, 20 cms across 1 segment, 4th cousins

MRCA 5G grandparents, born c 1733, 2 matches share 20 cMs across one segment, 6th cousins

MRCA 4G grandparents, born c 1776, shares 20 cMs across one segment, 5th cousins

Plugging 45 cMs into dnapainter suggests a very wide range of relationships, as close as 3rd cousin, as distant as 8th cousin or further.

Use the new filters if you are at Ancestry to look at all your matches between given ranges.Of my matches, those in the region of 40 cMs - 50 cMs are 3rd or 4th cousins, none more distant. Only one is unconfirmed because he has no tree, but using shared matches I know which line he belongs to, likely to be 3rd to 4th cousin as well.

So, speaking from my experience alone, I would think that 45 cMs is a lot closer than you are suggesting.

But it doesn't depend upon how many centuries ago, but how many generations ago the MRCA is on both lines. A family where the mother had several children from her 20s to her 50s, and where the oldest and youngest child followed the same pattern, there could be between 2 and 5 generations of her descendants born in one century.

If the pattern repeats itself you are unlikely to be a DNA match with any of the oldest group from 1800, whereas you could be DNA match with the youngest group from a lot earlier, even 1600s.

E.g. Tester born 1950, grandmother born 1910, 2G grandmother 1870, 4G grandmother 1830 etc
E.g,Tester born 1950, grandmother born 1850, 2G grandmother 1750, 4G grandmother 1650 etc.

Regards Margaret

[Gadget]

I think the century DNA measure would be dependent on you and your match's age.

I've just checked my common ancestors on Ancestry and find most of those that are in the approx 40-50 cM range are descended from my 3x grt grandparents, most of whom were born mid-1700s. However, there are quite a few with whom I link at that level who share a much lower cM, often dependent on the removal degree.

45cM shared DNA does sound a little large for, say, 4-6th grandparents and you might consider descent through more than one line.

Gadget

[NicVog]

Hi everyone, thanks very much for the succinct explanations. I'll continue looking for any more evidence I can find, DNA or otherwise.

[Mart 'n' Al]

Remember that the generation gaps vary.  My oldest great grandfather was born in 1837, and the youngest in 1876, 39 years apart.  39 years could often span three generations.

Martin