phenotypes are characteristics plants will have. IE/ you have 2 plants one is indica(a) one is sativa(b), if you bred them the off spring would (ab) now lets say your trying for a certain characteristic, lets say height.Now (a) has a dominant gene for short(1) and recessive for tall(2), while (b) is the opposite. If you bred them the off spring would/could possibly come out (a1b1)a mix of indica/sativa but a short plant,(a2b2) a mixed but tall,(a1b2) and (a2b1)mix that could either be short or tall as they both carry each strains dominant gene, in that case which ever pheno for height for Mj as a species would take dominance , hope thats clear