Daughters -- no sons
It seems a bit odd that none of the characters have given birth to sons, only daughters. Lou & Edie have three or four daughters, Murray & Marie have three daughters, and Ted & Georgette also have a daughter. (Murray and Ted each adopt a son.)
This seems odd, both from the real-world perspective (why was the show written that way?) and from the in-universe perspective (why would three men who work closely together just happen to have only daughters?).
Any answers?