Here's why:

* Genotype: The genetic makeup of an organism, represented by the combination of alleles (alternative forms of a gene) it carries. For example, a person might have the genotype "BB" for eye color, meaning they have two copies of the dominant "B" allele.

* Phenotype: The observable characteristics of an organism, which are determined by the interaction of its genotype with the environment. For example, a person with the genotype "BB" for eye color will likely have brown eyes, a phenotypic trait.

Therefore, genotype directly influences phenotype because the specific alleles an organism inherits determine the expression of traits. However, environmental factors can also influence the expression of certain traits, even with the same genotype.