From ISOGG Wiki
A genotype is an individual's collection of genes. The term also can refer to the two alleles inherited for a particular gene. The genotype is expressed when the information encoded in the genes' DNA is used to make protein and RNA molecules. The expression of the genotype contributes to the individual's observable traits, called the phenotype.
This article uses material in the public domain from the Talking Glossary of Genetic Terms and is reproduced courtesy of the National Human Genome Research Institute.