All I know about this is that tabby markings are very dominant. I had read up on this before Muffy had her kittens, and everything I read was right. I know her "boyfriend" was a black tom, and Muffy is a grey and black tabby. Of five kittens, 4 are tabbies and 1 is black.
Here's a link to a chart about cat color genetics. Maybe that will help you.