From: nospam@buzz.off   
      
   On Thu, 11 Sep 2025 22:09:39 +0100, the following appeared   
   in talk.origins, posted by Martin Harran   
   :   
      
   >I understand that we get half our DNA from each of our parents. How   
   >does that work backwards? I am into family research and have   
   >identified  all 8 of my great-grandparents; did each of them   
   >contribute exactly 1/8 of my DNA or is that an approximation?   
   >   
   AFAIK it's exact; each parent contributes one-half of the   
   genes for the offspring (I don't know how or if the X-Y size   
   difference affects this).   
      
   If I'm mistaken, someone will correct me. ;-)   
   >   
   >In my case, I have 8 distinct great-grandparents What happen if there   
   >is some cross-breeding? Let's say that two of my grandparents were   
   >cousins so I only have seven different great-grandparents, Would that   
   >mean one of the 7 would have contributed 1/4 of my genes and the other   
   >six contributing 1/8 ?   
   >   
   Even if they were cousins, their genetics are not identical;   
   probably not even close. Only identical twins or clones have   
   identical genetics, Again, AFAIK.   
   >   
   --   
      
   Bob C.   
      
   "The most exciting phrase to hear in science,   
    the one that heralds new discoveries, is not   
    'Eureka!' but 'That's funny...'"   
      
   - Isaac Asimov   
      
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