gpg --expert --gen-key
(certify only)
gpg --edit-key Alice
addkey sign
addkey encrypt

Now we have:

$ gpg -k
/home/alice/.gnupg/pubring.gpg
-------------------------------
pub   4096R/DCAAB3AB 2015-07-06
uid                  Alice
sub   4096R/17A1DF65 2015-07-06
sub   4096R/25FF3FEC 2015-07-06

and:

$ gpg -K
/home/alice/.gnupg/secring.gpg
-------------------------------
sec   4096R/DCAAB3AB 2015-07-06
uid                  Alice
ssb   4096R/17A1DF65 2015-07-06
ssb   4096R/25FF3FEC 2015-07-06

gpg --output=alice.primary.pub.key --armour --export Alice
gpg --output=alice.primary.sec.key --armour --export-secret-keys Alice
gpg --output=alice.sec.sub.keys --armour --export-secret-subkeys 17A1DF65! 25FF3FEC!

gpg --delete-secret-and-public-keys Alice
gpg --import alice.sec.sub.keys && gpg --import alice.primary.pub.key