Mac OSX Yosemite no serial ports showing for Uno R3
Probably, you have Chinese Uno analog which works on CH340 USB-to-serial chip, so you need to install driver for it.

Steps to fix:


Install the CH340 driver
Run the command in Terminal: sudo nvram boot-args="kext-dev-mode=1" (disable kext signing introduced in Mac OS X 10.9 Yosemite)
Reboot


Also you're right according to Uno and FDTI:


  Differences with other boards
  
  The Uno differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter.