How does the Boeing 777's yoke of both the captain and the first officer have synchronized movement?
From the FCOM v2 (9.20.1):


  The primary flight control system uses conventional control wheel, column, and
  pedal inputs from the pilot to electronically command the flight control surfaces.
  The system provides conventional control feel and pitch responses to speed and
  trim changes. The system electronic components provide enhanced handling
  qualities and reduce pilot workload.
  
  [...]
  
  The columns and wheels are connected through jam override mechanisms. If a
  jam occurs in a column or wheel, the pilots can maintain control by applying force
  to the other column or wheel to overcome the jam.
  
  The rudder pedals are rigidly connected between the two sides.


So yes, there is a direct mechanical link between the control columns, but it can be overridden.



Edit:

As John K pointed out in the comments, the technical term for the mechanical link is a torque tube with a breakout mechanism. The details are described in patent US5782436A:


  When a sufficient amount of force is exerted on the un-jammed control, the connection of the swivel arm to one side of the torque tube will disconnect due to the force applied overcoming the force of the spring holding connection in place.