You would have two separate spell lists.
Your sorc level and charisma ability would determine how many spells you can cast per day, what spells you know, the DC, caster level, etc. from spell on the sorc spell list.
Your wizard level and intelligence would determine how many spells you can cast per day, what spells you know, the DC, caster level, etc. for the wizard spells.
Even though they are the same spells, you could only cast some as a wizard, and some as a sorcerer... does that make sense?
See: [Lore]caster level[/lore], [lore]wizard[/lore], [lore]sorcerer[/lore], and [lore]bonus spells[/lore]
Now keep in mind, you could make a very compelling RP reason why a character would be a wizard/sorc but you would be handicapping yourself mechanically compared to going with just one or the other.
