I installed the Public Beta of 10.10 this morning on a new partition on my SSD. After setting it up I wanted to return to my main system only to find it was no longer available after booting with the option key. I had read Yosemite would mess with partitions but my only options are to boot to my Yosemite partition or a recovery partition. Not my SSD or HDD. I didn't backup. Such a stupid rookie mistake. I just didn't foresee losing my option to boot to my main system. Any advice would be sincerely appreciated.