Final answer:
A genotype is the complete genetic makeup of an organism, consisting of all the inherited alleles for every gene. It is represented by allele combinations like TT, Tt, or tt and is distinct from the phenotype, which is the observable expression of the genes.
Step-by-step explanation:
The most accurate definition of a genotype is the complete genetic makeup of an individual organism. This includes all the genes that were inherited from the organism's parents. For each gene, an individual has two alleles, one from each parent. For instance, if we consider a gene that determines the color of a plant's pods, there can be different combinations of alleles like TT, Tt, or tt, indicating different genotypes. These combinations represent whether the alleles are homozygous (both alleles the same) or heterozygous (two different alleles).
Mendel's hybridization experiments illustrated the concept of genotype through the inheritance of pod color in pea plants. A homozygous plant with yellow pods (YY) crossed with a homozygous plant with green pods (gg) would result in F1 offspring with a heterozygous genotype (Yg), but with a yellow pod phenotype, showing that the genotype is distinct from the phenotype, which is the observable expression of the genes.