Anyways the way the letters are written seem to have evolved over time (duh) and http://medievalwriting.50megs.com/scripts/letters/letters.htm has lots of information about this. The lower case 'a' has the "hook" or "bowl" styles with the bowl also being called the italic style even though many non-italic fonts use this style as well.
'g' has several different shapes, with or without a closed loop (bowl) at the bottom or connecting the bowl on the right or left side of the letter. Apparently the 'g' with the bowl decreases the length of the descender (part that goes below the line) allowing more lines to fit on a page.
If you wanted to go more in depth I'm sure there's lots of information out there about ascenders, descenders, hooks and bowls but I think that's the limit for me.