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The genotype of an organism refers to its actual genetic makeup, which includes the specific alleles and genes present in the individual's DNA. This term encompasses both the dominant and recessive traits inherited from the parents, regardless of whether those traits are expressed in the organism's observable features.

For instance, an organism may carry alleles for a particular trait that are not currently expressed due to various factors, including the influence of dominant alleles. The genotype is foundational to understanding inheritance, as it determines the potential for traits to be passed on to future generations, even if they are not outwardly visible in the organism itself.

Observable characteristics represent the phenotype, which is shaped by both genotype and environmental factors. External influences on appearance are factors that can alter how a genotype is expressed but do not change the actual genetic code. The effect of mutations refers specifically to changes in the DNA sequence that can potentially alter the genotype but does not define it. Thus, the actual gene makeup is the most accurate representation of an organism's genotype.