it's a way of expressing genetic combo's from both parents- A and B..A(a) and B(b) represent specific distinguishing characteristics .crossed, they look like this: Ab, Ba,Aa,Bb....then it goes further with each recombination or outcross:AbaB,bAab,ABbA,etc. thus we get genetic diversity, and individuals...not every Jordan is michael Jordan! the more complex an organism is, the less chance of 2 of a kind.