Effect of cousins marrying cousins

[LadyAlaise]

There seems to be some dispute among the experts on this, but several have told me that a history of cousin marriage, especially when combined with very large family size, can "convince" the matching algorithm that the relationship is closer than it really is. This is certainly the case with descendants of my own French-Canadian ancestry.

I am no expert in genetics but to me it seems to make sense; I also have a lot of Acadian French ancestry with many many many overlappings of 3rd-5th cousins marrying on many generations in many branches of my tree. (we acadian genealogists like to joke that we have Family Fishnets not Family Trees perse), another reason I am looking forward to getting my ff results I have many Acadian cousins waiting to see how closely we match due to having multiple different generational family tree connections (ie: SoandSo is my 5th cousins through X line and my 7th cousin through Y line and my 4th cousin through Z line) or another example; my paternal Grandparents, going Up their Trees from them, were 3rd THROUGH 11th cousins respectively to each other..

[T E Peterman]

I am descended from a few cases where there were first cousin marriages. I have found at AncestryDNA, that nearly half of my leaf hinted distant matches come through these cousin marriages. It amplifies the signal; makes the algorithms estimate a closer kinship & thus "see" a lot farther. A distant cousin that you connect to through that intermarriage will be a lot more likely to turn up as a match.

I have been describing 1st cousin marriages. The effect would diminish considerably at the 2nd cousin level & even moreso at the 3rd or 4th cousin level.

Timothy Peterman

[192971]

It seems a few of my ancestors married 3rd and 4th cousins, including my own GGrandparents.

How does this effect my DNA results, or is there no effect from it?

My father is 5th cousin of himself, via a ancestor couple who seem to be unexpectedly reliable in connecting me to FF matches on my paternal side. But of course it has been a random shuffle; I, or anybody descending from the ancestral couple in question, still could have ended up getting insignificant amount of DNA from them. It only have had lower probability to happen.

The genetics word "recombination" itself gives us a clue that there must be an effect of what is recombined. If the replaced part is totally different to replacing part, recombination is efficient, but in the other end, if the replaced and replacing parts are totally identical, recombination is like it never happened.

[hfp43]

It seems a few of my ancestors married 3rd and 4th cousins, including my own GGrandparents.

How does this effect my DNA results, or is there no effect from it?

Does anyone know?

Thanks.

There seems to be some dispute among the experts on this, but several have told me that a history of cousin marriage, especially when combined with very large family size, can "convince" the matching algorithm that the relationship is closer than it really is. This is certainly the case with descendants of my own French-Canadian ancestry.

[Chester]

It seems a few of my ancestors married 3rd and 4th cousins, including my own GGrandparents.

How does this effect my DNA results, or is there no effect from it?

Does anyone know?

Thanks.