Law of dominance :

• In a heterozygous plant, out of two contrasting characters only one express its character and suppress the other. One who express its character is called dominant and other is suppressed is called recessive.
• Eg: When a tall (TT) plant is crossed with a dwarf plant (tt) in F1 generation, all plants are tall (TT). They have received the factors of both tallness and dwarfness but the tall is dominant over the dwarfness. So, tall is expressed and dwarfness is recessive.