Number of ancestors

[gatty]

How many 5gt grandparents do i have if 3 of my 3gt grandparents had the same grandparents? I think it's 124 but i'm not sure.

[prairielad]

If all 3 of your 3xgreat grandparents where full siblings, you would have 60 distinct 4xgr grandparents and 120 distinct 5xgr grandparents

Each sibling has 4 grandparents, so 4+4+4=12. Therefore out of your 128 5x gr grandparent you can subtract 8

Hope that make sense

[gatty]

Didn't explain very well. Sorry. 3 of my 3 gt have the same pair of grandparents but it is the three 4gt that are siblings.
Does that change things?

[T E Peterman]

I concur with 124. You have 64 g-g-g-g grandparents, 3 of whom are siblings. In the next generation the total amount would normally go to 128 & the 3 would lead to 6 more ancestors, but since they are siblings, they only lead to 2 more ancestors, a net loss of 4 at the g-g-g-g-g grandparent generation.

Timothy Peterman

[Earl Davis]

If you search on the net for the term ‘pedigree collapse’ you should find some interesting articles on this subject.
The genealogy program I use lets you include or exclude ‘duplicate’ ancestors on the pedigree charts it produces. I like to include them so you can see how many times the same ancestor appears in say generation 10. I have many examples of pedigree collapse in my own tree. My own parents turned out to be 5th cousins (unknown to them) as did my wife’s great grandparents.