Since you say Google mail I assume your referring to gMail.  The only way to not have them synced is to use the POP download option in the settings. 

Why would you want to do this?  gMail is built on a platform that is specifically designed to make sure all your devices are always synced.  POP mail is old technology and much more difficult and time consuming to manage.  It offloads data off a central server and creates multiple copies of it if you use multiple devices.  It requires you to make backups of individual devices/computers and also makes moving to a new device much more difficult.  I also suggest that if you're using a frontend software program such as Windows Mail, Microsoft Outlook, or Thunderbird that you simply use the web interface.  Once again, its so universal.  For instance, I have three computers I regularly use, an iPhone and an iPad.  My wife also has a PC in her office.  I just replaced my office desktop.  I store the majority of my information on cloud based servers so that I can get at the information from any device, any time, and any where.