Final answer:
Mendel's experiments led to the conclusion that individuals carry two alleles for each trait, which make up their genotype and determine their phenotype.
Step-by-step explanation:
From his experiments, Gregor Mendel concluded that each individual carries two factors or alleles that govern the inheritance of each trait. Alleles are different versions of a gene that sit at the same locus on homologous chromosomes and are responsible for the variations in inherited characteristics. An individual's genotype consists of the alleles they possess for a given gene, and these alleles can be either homozygous (same alleles) or heterozygous (different alleles). The observable characteristics, or phenotype, are the expression of an organism's genotype in conjunction with the organism's environment.