Why does P1 look all alike and F1 looks very different?

p1 look all like because their allen are always all the same,and its offspring will be identical as its parent.When Mendel let two differert plants doing sex,their children F1 will choose the dominant allen between their parent,and they will always become that.For example,if a tall plant is sex with another short plant,and the tall allen is dominant.For this reaason,their children will all become tall.The short allen are recessive,but it will be affect their grandchildren.