When Gregor Mendel crossed true-breeding tall plants with true-breeding short plants What type of inheritance is it?

Complete dominance

Explanation:

Gregor Mendel (1822 - 1884) was regarded as the "FATHER OF GENETICS" due to his immense contribution to discovering the principles that govern inheritance in organisms. In one of his several experiments, he performed a cross between true-breeding tall plants (TT) and true-breeding short plants (tt).

From this cross, Mendel found out that the F1 generation were all tall. He self-crossed the F1 generation and obtained F2 offsprings in a ratio 3 tall: 1 short. This shows that the tall phenotype allele (T) is dominant over the short phenotype/allele (t), which was being masked in the F1 generation i.e. Tt. This inheritance pattern is called COMPLETE DOMINANCE.