Are women allowed to ride in the Tour/Giro?

[TxDoc]

I am so curious if anyone knows whether women can officially compete in major tours like the Tour de France or the Giro d'italia?

Are there major professional cycling teams with women on them, or made up entirely of women riders?

There is a "giro donna" that is exactly the giro for women's teams, and a "TdF feminin" aka the TdF for women's teams. You can see:
http://www.girodonne.it
http://www.velo-feminin.com