When two sisters marry two brothers, their children have the same two sets of grandparents.
Unlike most people, who have a cousin that has grandparents that you've never met or care about; these cousins share both sets of grandparents.
Divorce is very hard for these families, if divorce happens to one set of these parents, every family get-together is a fight between the still married couple, the wife wanting her sister present and the husband wanting his brother present, but neither one of those people wanting to be around their divorce' Jane Smith wanted her sister Jill Smith to meet her boyfriend, so Jane and Jill decided to set up a double date. Now Jane and John are divorced, family get-togethers SUCK!
It's rare, but I don't know of any statistics to say how rare.
I have a set of ancestors, two brothers who married two sisters. Except that each couple had a child, a boy and a girl, and they married each other, so the gene pool got smaller at that point.
My sister married my husband's brother (so we have two brothers who married two sisters).
We are all curious about how related our children will be.
(I'm pregnant with our first child right now.) I understand siblings share 50% of the same genes.
In our case would the first cousins be as genetically related as siblings?
If no - can you tell us exactly how related they will be?
-A curious adult from Canada February 24, 2005 What a fun question. The quick answer is that I think the kids would end up being somewhere between siblings and first cousins.
This wasn't as easy to figure out as it might seem...