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Author Topic: How much DNA do I share with a cousin if our fathers are identical twins?  (Read 9323 times)

Offline Jossie77

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I've been wondering ... my father is an identical twin.

If a DNA test were done on my cousin and I ... would we, genetically speaking, appear to be half-siblings?
« Last Edit: 16/03/2013 22:27:06 by chris »


 

Offline evan_au

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Re: Children of Twins
« Reply #1 on: 16/03/2013 02:28:46 »
Yes, the DNA of your father & uncle are "identical", ie they started off with the same DNA as a single egg. So your cousin and yourself would appear to be step-sisters half-sisters.

In the 60 or so cell divisions until they each became adults, a number of different "de novo" (new) mutations would have occurred in your father and uncle; this is likely to cause part of the medical differences which occur between identical twins, which are usually attributed to "environment" rather than "genetics".

These could probably be distinguished with a full-genome sequence of yourself, your siblings and your cousin(s).
« Last Edit: 16/03/2013 05:17:18 by evan_au »
 

Offline CliffordK

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Re: Children of Twins
« Reply #2 on: 16/03/2013 04:36:33 »
SO your cousin and yourself would appear to be step-sisters.
Step siblings are siblings through marriage, and otherwise unrelated.

Jossie & her cousin would genetically appear to be half-siblings (genetically identical fathers, different mothers), although, as Evan mentioned, there may be some denovo mutations in the paternal half of the genome that could be detected with full DNA sequencing, of both fathers and children, but not with the routine DNA/paternity testing.
 

Offline Jossie77

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Re: Children of Twins
« Reply #3 on: 16/03/2013 13:46:09 »
Thanks! I thought that was the case but I was never sure. Its one of those things that got my curiosity up a couple of years ago. Its an interesting little fact.
 

Offline Lmnre

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Re: Children of Twins
« Reply #4 on: 16/03/2013 17:29:37 »
I knew identical twins who married identical twins and all their children were genetic siblings!
 

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Re: Children of Twins
« Reply #4 on: 16/03/2013 17:29:37 »

 

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