The phenotype, a product of genotype, is the observable traits or characteristics of an organism, for example hair color, weight, or the presence or absence of a disease, except the genes themselves.[1] Differences in phenotype are caused by differences in genotype, but not all phenotypes necessarily have the same genotype. Organisms that contain a dominant allele and a recessive allele for a trait will have the same phenotype as an organism that has two of the same alleles for the dominant trait.