Q: If a set of identical twin women married a set of identical twin men and subsequently had children would their children genetically be siblings? I think they will, my friend A.J. says I am crazy. Help! (Juliana, Casselberry, Florida)

A:  You are right; A.J. is wrong. All the children in both families are genetic siblings, in addition to being just plain siblings within each family.

The fathers (blue) of families A and B are identical twins; likewise, the mothers (red) are identical twins. Therefore, all of their children (yellow) are genetic siblings.