Forum:ME2 Experience

There is a great and informative page on this wiki about Experience in ME1, but nothing I can find about ME2. I see in the walkthrough that xp is awarded after mission or assignment completion, usually with two different values shown, one in parentheses. For example, "Experience: 1,000 (1,250)". What does this mean? If you type "experience" into the wiki's search bar, you only get info on ME1, which of course uses a completely different xp method.