Why is blood relationship between cousins 1/16?

Question

So I was playing around with genealogy options on Wolfram|Alpha. I started to wonder how it calculates particular blood relationship. It makes sense that one has inherited 1 part of blood from each of their grandparents. Each person had 4 grandparents, so blood relationship to one grandparent is 1/4. For two people there would be 8 grandparents, so one of them would be 1/8 Cousins have two grandparents in common so that makes six different people, that would make one grandparent 1/6. I can imagine that since there are two common grandparents their share of blood is expresed as 2, so 1/16 probably comes from 2*8, but I don't really understand why they would express it like that - why not 2/8 and why would they treat common relatives as different people

gardengallivant · Accepted Answer

Chromosomes come in pairs that assort independently so you inherit a random half from each parent wh got random sets from their parents.

Grandparents pass their chromosomes thru parents to progeny so each pass on about 25% of the chromosomes.  First cousins to this progeny share 12.5% or 1 in eight chromosomes in common from their shared grandparents being on reproductive step farther removed.

Look this site over
http://www.tevern.us/gen/Cousins/index.htm

Roland · Answer

You have 1/2 from your father, he has 1/2 from your grandparents, 
your uncle has 1/2 from those same grandparents, your cousin has 1/2 from your uncle.
1/2 x 1/2 x/1/2 x 1/2 = 1/16.

Maybe this is how . . .

Anonymous · Answer

So we can sex our cousins and only have a 1 in 16 chance of the kid begin retarded. It's god's way of saying "love thy family".

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Why is blood relationship between cousins 1/16?

3 Answers