How do Mendel's experiments show that traits are inherited independently?

(N/A) Mendel performed a dihybrid cross by crossing pea plants having round green seeds $(RRyy)$ with pea plants having wrinkled yellow seeds $(rrYY)$.
In the $F_1$ generation,all plants produced round yellow seeds $(RrYy)$ because round and yellow are dominant traits.
When these $F_1$ plants were self-pollinated,the $F_2$ progeny showed four types of combinations: yellow round,green round,yellow wrinkled,and green wrinkled seeds in a phenotypic ratio of $9:3:3:1$.
The appearance of new combinations (green round and yellow wrinkled seeds) in the $F_2$ generation,which were not present in the parents,clearly demonstrates that the traits for seed shape and seed color are inherited independently of each other.