Why did Mendel used two traits like yy or tt why didn't he use one trait like y or t

Biology 1c cumulative exam i need awsners

Arrange the following in the correct sequence, from earliest to most recent, in which these plant traits originated. 1. sporophyte dominance, gametophyte independence 2. sporophyte dominance, gametophyte dependence 3. gametophyte dominance, sporophyte dependence a) 1 → 2 → 3 b) 2 → 3 → 1 c) 2 → 1 → 3 d) 3 → 2 → 1 e) 3 → 1 → 2

Guard cells control which event? the growth of plants capture of solar energy gas exchange in leaves water absorption in roots