Final answer:
Having the alleles Tt represents an organism's genotype, which is the specific combination of alleles for a gene. Genotype determines the potential phenotype, which is the observable traits of an organism. Thus, the option c is the correct answer.
Step-by-step explanation:
When discussing genotype and phenotype, having the alleles Tt refers to an organism's genotype. A genotype is the combination of alleles that an individual has for a certain gene. For example, an organism could have the genotype TT (homozygous dominant), Tt (heterozygous), or tt (homozygous recessive). The phenotype, on the other hand, is the observable physical characteristics that result from the interaction of the alleles. For instance, if T represents the dominant allele for tallness in pea plants, and t represents the recessive short allele, a plant with the Tt genotype would be phenotypically tall, although its genotype indicates that it carries both tall and short allele forms.