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Old 12th January 2015, 08:33 PM
GoneResearching GoneResearching is offline
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How is total cM or percentage shared Effected By Being My Own Cousin With Cousins of

I have seen a few Relationship Charts that show the possible avg. percentage of DNA In Common based on how you are related to another person. And I have seen articles talking about likely/possible amount of total avg. cM in common ranges based on specific relationship levels.

BUT has anyone at FamilyTreeDNA or elsewhere figured out how being your own cousin affects those numbers/percentages with cousins of that branch? I assume they would go up but by how much – a little or a lot?

If what I suspect in my lineage is correct …

One set of my fourth great grandparents were first cousins that married so their grandparents (my sixth great grandparents) are the common ancestors making me a seventh cousin to myself. I have found DNA matches to several sixth cousins and a seventh cousin (I think because I’m still waiting to learn the rest of his lineage to figure the exact relation) for this branch of my tree. The common ancestors with the sixth cousins are the parents of my fourth great grandma (who married her first cousin) so I am really double-related to them. I’m their sixth cousin through my fourth great grandmother and seventh cousin through her husband/my fourth great grandfather. How does my double dose of kinship affect the likely avg total cM range or the percentage shared we share? Normally the avg. percentage shared for sixth cousins is listed at 0.0122% or 0.83 cM. Does anyone know how much it could potentially be increased?

Now for the seventh cousin also on this same branch the common ancestors are the sixth great grandparents. In this case I am a seventh cousin to this person through my fourth great grandmother and a seventh cousin through her husband my fourth great grandfather. How does my double dose of kinship affect the likely avg total cM range or the percentage shared we share? Normally the avg. percentage shared for seventh cousins is listed as 0.00305% or 0.21 cM. Does anyone know how much it could potentially be increased?

If the total CM range or the percentage shared is much higher than “normal” with these cousin situations would this add weight to the two first cousins married situation?

Also, if the suspected fourth great grandparents were half-first cousins instead of full-first cousins how would that effect avg. total cM range or percentage shared? In the case of the seventh cousin, I would be a full seventh cousin and a half seventh cousin to that person.

If there is an article about this kind of situation, please point the way to finding it.
I hope someone has an idea of what happens in this type of situation.

Regards
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Old 12th January 2015, 08:45 PM
tlgarrison tlgarrison is offline
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Quote:
Originally Posted by GoneResearching View Post
I have seen a few Relationship

BUT has anyone at FamilyTreeDNA or elsewhere figured out how being your own cousin affects those numbers/percentages with cousins of that branch? I assume they would go up but by how much – a little or a lot?
Regards
I have a couple lines with first cousin marriages and yes it affects the the outcome of the Algorithm used to calculate the estimated generations to your common ancestor with your matches along the same lines. For instance if your are a descendant of a 1st cousin marriage your estimated generations to common ancestor with a match along the same line will be wrong and is probably about twice the generations listed. 2nd cousin marriages would not be as much but would still bump up the total cM's shared between their descendants down the line.
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Old 17th February 2015, 05:30 PM
Adam Nisbett Adam Nisbett is offline
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I'm not a scientific expert on the subject, but based on my understanding of how DNA is passed, I think being your own cousin would be DNA equivalent of being one generation closer than otherwise. i.e. a 4th cousin along the repeated line, would share DNA equivalent to a typical 3rd cousin 1x removed relationship.
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Old 17th February 2015, 05:32 PM
Adam Nisbett Adam Nisbett is offline
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At that distance though (6th-7th cousin) the variance in how much DNA is typically shared is probably nearly as great as the difference made by your double dose of DNA.
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Old 8th July 2017, 08:22 PM
dove6338 dove6338 is offline
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How to manually add double kinship links in the pedigree tree

This is not really a reply to the previous discussion about double kinship but a new question about how to manually add people that are double kin. When using the Family Finder Family Matching Tool, how do you add a lineage that has a double kinship using manual additions? There does not appear to be a way to link a double kinship except by downloading a gedcom file. Is this correct? If a man and woman are second cousins (and second cousins to me) I can add their individual lines but I cannot link them as husband and wife or I can link them as husband and wife but cannot link one of them to their ancestral line.
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