question on seeds

[encore]

just was wondering, if you have a heirloom tomato plant, lets just say black krim, as an example, now you don't bag the blossoms, but you save seeds from one of the tomatoes, chances are good that they won't be black krim plants, but my question is: will all the seeds in that tomato that you saved, be the same? or could the seeds produce a variety of differant plants?--thanks -tom