In his experiment mendel first crossed tall and short peas plant and noticed that the F1 plants were all tall. in the second experiment he crossed the the F1 plants and noticed that short plants reappeared in the rate of 25% in F2 generation. in his third experiment he crossed he crossed F2 plants and noticed that when he crossed some tall plants with the shot plants the F3 generation contained short plant in frequency of 50%. after this observations mendel concluded that there were genes that could be only expressed in homozygous state but not in heterozygous state. these genes were later referred to as recessive alleles wheres the genes that prevented the expression of recessive genes were later referred to as dominant genes.
