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      Get Smart on the Web   09/16/2016

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Guest Dj

Double Second Cousins

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Guest Dj   
Guest Dj

DOUBLE SECOND cousins: 

 

Male 1 had children with Female 1. One of their children then had children with an unrelated person and I was born.

 

Then Male 2, who is brother to Male 1 had kids with Female 2 who is sister to Female 1. One of their kids had children with an unrelated person and the result is my second double cousin.

 

My question is: How related are me and my DOUBLE second cousin? Our most recent related ancestor would be our great grandfather and great grandmother. Are we as related as normal second cousins or are we closer? 

Does this mean we have any greater chance of having an affected child? If so, how much percentage? What would you advise us to do?

 

Thank you!

 

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LadyC    98

this is really a question better suited for a genetic counselor. what i can tell you is that second cousins have no higher risk than unrelated couples have when it comes to passing on autosomal recessive disorders to their children. and first cousins have only a 1.2 to 2.8% higher risk than unrelated couples of passing on a recessive condition.

as double second cousins, i'd say that no matter how you slice it, the risk is very minimal. but i'm not an expert. your insurance should cover genetic counseling, and your primary care physician can refer you to one.

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Guest Ava   
Guest Ava

I was under the impression that double second cousins are related like 1st cousins in the dna sense.

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LadyC    98

ava, are you dj's cousin? ya'll are welcome to join, then your posts will be automatically approved :)

as i said.. regular second cousins would have no increased risk. first cousins have a 1.2 to 2.8% higher risk than unrelated couples. so no matter how you slice it, your risks are very minimal. you asked how high the risk is and what the percentage is. that's the answer. and we always encourage couples to see a genetic counselor if they have any concerns.

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YTB2Her    1

My first comment would be one of simple mathematics. 

You share a single common ancestor, your great-great-grandparent, their spouse (your other great grand parent) was unrelated to your DNA. 

Your respective grandparents shared 50% of their DNA because of dilution by their spouses.

So then your respective parents shared 25% of their DNA because of dilution by their spouses. 

That being the case, you and your 'cousin' each share 12.5% of your DNA being diluted by your 'other' parents  

That being the case, if you and your 'cousin' had children they would share 6.25% of their DNA  

 

With 6.25% of their DNA in common, your children wouldn't be much different that most of rural Europe, Asia and Africa  

 

BTW, I have the above down cold because my wife and I are EXACTLY the same relations as you two are, my grandfather and hers were brothers  

 

 

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LadyC    98

thanks ytb! i am not good at math and didn't want to go look it up (even thought it is in our info pages.) it's always easier for me to remember the risk factor than the dna.

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