[jQuery] Remove comma

Hello,
I have the following code:
$levels = $('input[name="Levels"]:checked + label');
levels = $levels.map(function() { return $(this).text(); }).get();
$theme.append(levels.join(", ")).append('<br />');
How can I replace the last comma in levels by " and "?
I tried:
levels.join(", ").replace(/, $/,'and ')
This is not working.
Could someone, please, help me?
Thanks,
Miguel