Answer:
genotype is responsible for establishing phenotype
Step-by-step explanation:
When Mendel experimented with pea plants, concept of genes and alleles had not come up yet. Through his experiments Mendel first proved that some type of combination in cells leads to a particular phenotype.
He coined the term "factors" which are today known as alleles. These factors paired up and displayed a particular phenotype. Today we know that the alleles are responsible for a genotype which ultimately results in a phenotype. Hence, he established that genotype is responsible for establishing phenotype even before the term genotype was coined.