Only 62

[darkerhorse]

Since my paternal grandparents were 3rd cousins to each other, I have only 62 4x great-grandparents instead of the usual 64.

Would I have likely inherited a disproportionately larger amount of DNA from the shared couple?

Would I have then inherited more than 50% of DNA from my father?

[MarcuccioV]

Maybe yes, maybe no. Unfortunately, replication is completely random. You could get DNA from one of them and get none from the other. There is no mathematical equation to figure it out. Nature hates math.

Oh, the joys of genetics...

[darkerhorse]

Wouldn't the odds be in favor of it?

Wouldn't that couple have twice the chance to contribute DNA?

Picking names out of a hat is random, but if two names are in there twice, don't they have twice the chance of being selected?

Yes, in any given case you never know, but in the long run...

So, over a large sample of persons with grandparents related by blood, wouldn't the shared couple be expected to contribute DNA more or more often?

[MarcuccioV]

It's anybody's guess. Nature also doesn't like rules...

[joetucciarone]

In my opinion, you'd probably still inherit 50% of your DNA from your father, statistically speaking. But, the probability is that the DNA you got from your paternal grandparents would be a proportionally larger fraction of your Dad's DNA than the share you've received from your maternal grandparents. For example, I have a cousin with whom who I share significantly more DNA than expected, considering our positions in the family tree. But we also share two different pairs of 3x great-grandparents on two different branches of our family tree, which might explain our greater-than-expected DNA match.

[darkerhorse]

In my opinion, you'd probably still inherit 50% of your DNA from your father, statistically speaking. But, the probability is that the DNA you got from your paternal grandparents would be a proportionally larger fraction of your Dad's DNA than the share you've received from your maternal grandparents. For example, I have a cousin with whom who I share significantly more DNA than expected, considering our positions in the family tree. But we also share two different pairs of 3x great-grandparents on two different branches of our family tree, which might explain our greater-than-expected DNA match.

It has to be that way, not for any given case (though it was in yours), but overall.

[darkerhorse]

In my opinion, you'd probably still inherit 50% of your DNA from your father, statistically speaking. But, the probability is that the DNA you got from your paternal grandparents would be a proportionally larger fraction of your Dad's DNA than the share you've received from your maternal grandparents.

This seems confusing. Can you give an example with percentages?

[joetucciarone]

Sorry, I was on vacation and I missed your question. You have 32 great-great-great-grandparents. If each of them was a unique person, you'd (statistically) inherit 1/32 of your DNA from each of them. In other words, each of them (statistically) contributed 3.125% of your DNA. Since two of your paternal grandparents were 3rd cousins, you actually have 30 unique great-great-great-grandparents, 16 on your mother's side and 14 on your father's side. That means (statically) the DNA you inherited from each paternal great-great-grandparent is 3.571% compared to the 3.125% you received from each of your maternal great-great-great-grandparents.

[joetucciarone]

I need to amend the percentage 3.571% in my last note. That's the average contribution from each of your 14 paternal great-great-grandparents. But each of the two of them who are not unique contributed 6.25% of your total DNA. Since these two people contributed twice to your DNA pool, each of them contributed twice the usual 3.125%, which is 6.25%. Again, that's based on pure statistics.

[darkerhorse]

By paper trail, my father was 100% Italian (Sicilian) and my mother was 0% Italian. So, I'm likely a little more than 50% Italian (Sicilian)? If yes, what is the statistic, 56.25%?

Also, I have relatives whose parents were 1st cousins and relatives whose parents were 2nd cousins. So, the contribution effect is enhanced?

[MarcuccioV]

By paper trail, my father was 100% Italian (Sicilian) and my mother was 0% Italian. So, I'm likely a little more than 50% Italian (Sicilian)? If yes, what is the statistic, 56.25%?

Also, I have relatives whose parents were 1st cousins and relatives whose parents were 2nd cousins. So, the contribution effect is enhanced?

I don't believe it works that way. You still get 50% DNA from each parent. What it means is of the 50% of DNA you inherited from your father, you may have received a higher percentage from those 2 relatives. Again, DNA replication is random, so there's no guarantee even of that.

Same goes for the other relations. It only affects that side (maternal or paternal). There is no crossover. It remains 50/50.

In any case, this would have no effect on what you received from your mother; only the mixed percentages you obtained from your father's side.

[MarcuccioV]

The ONLY exception would be if your PARENTS were related...

[darkerhorse]

Yeah, I realized my error shortly after posting it.

The husband of the duplicate couple happens to bear my surname, so I'm a true bluer.

I guess my relatives whose grandparents were 2nd cousins to each other. Again, our surname was involved.

The relative whose parents were 1st cousins doesn't involve the surname. What would the statistical percentage be for them? 9.375%? from each? That's a lot.

My parents were not related to each other, thank heavens.

[MarcuccioV]

Statistics and reality unfortunately don't always agree. Being that you're dealing with a single ethnicity, it would be nearly impossible to tell who you received your combinations of DNA from. On the Sicilian side, there is very likely to be mixes of Greek, West Asian, Baltic, North African, Anatolian, etc (I have most of those just from the percentage of Sicilian my grandfather carried -- and I don't even know what that percentage is, probably 10-25%).

Since DNA replication is so very random, It's completely possible that one of these relatives was completely "skipped over". It happens. If you have siblings, your percentages will almost assuredly be different from one another.

Comparing DNA matches (which you & your relatives would need to do DNA tests to get), COULD help you to narrow it down somewhat. Possibly. And possibly not.

Not to add to the confusion, but here is an example based on my "mystery cousin' (no longer so much a mystery). We both have equivalent results for Italian percentage, but we are opposites in south vs north (I am 3:1 south & she is 3:1 north).

The reason is my mother favored my grandfather who was more 'southern'. Of the 50% of my DNA I got from her, I got (by pure chance) a higher percentage of HIS DNA than I did from my grandmother.

In my cousin's case, her father (my uncle) favored my grandmother who was more northern, giving her more of that side (again, simply through a roll of the genetic "dice"). This continues for generations further back as well. The 50% rule ONLY applies to successive generations. Prior to that it's a crapshoot.

That's just the long & short of it. There are plenty of articles online that explain it more scientifically than I have here. But that is the basic idea.

[MarcuccioV]

Since my paternal grandparents were 3rd cousins to each other, I have only 62 4x great-grandparents instead of the usual 64.

Would I have likely inherited a disproportionately larger amount of DNA from the shared couple?

Would I have then inherited more than 50% of DNA from my father?

So in continuing my family research, I believe I have found a very similar (if not identical) situation -- same pair of 4GG's on one of my grandfather's lines.

Turns out my grandfather's grandparents from his father's mother were a Giuseppe Piacentini and Leonilde Pizzuti.

His grandparents from his mother's father were ALSO Giuseppe Piacentini and Leonilde Pizzuti.

Sounds like the same relationship to me. And we're probably not the only ones sharing this scenario, either...