A genotype is an organism’s complete set of heritable genes, or genes that can be passed down from parents to offspring.[1] These genes help encode the characteristics that are physically expressed (phenotype) in an organism, such as hair color, height, etc.[2] The term was coined by the Danish botanist, plant physiologist and geneticist Wilhelm Johannsen in 1903.[3]
Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal colour in a pea plant. The letters B and b represent alleles for colour and the pictures show the resultant flowers.
The genotype is one of three factors that determine phenotype, along with inherited epigenetic factors and non-inherited environmental factors. Not all organisms with the same genotype look or act the same way because appearance and behavior are modified by environmental and growing conditions. Likewise, not all organisms that look alike necessarily have the same genotype.
One's genotype differs subtly from one's genomic flash card sequence,[clarification needed] because it refers to how an individual differs or is specialized within a group of individuals or a species. So, typically, one refers to an individual's genotype with regard to a particular gene of interest and the combination of alleles the individual carries (see homozygous, heterozygous).[4] Genotypes are often denoted with letters, for example Bb, where B stands for one allele and b for another.
Somatic mutations that are acquired rather than inherited, such as those in cancers, are not part of the individual's genotype. Hence, scientists and physicians sometimes talk about the genotype of a particular cancer, that is, of the disease as distinct from the diseased.
An example of a characteristic determined by a genotype is the petal color in a pea plant. The collection of all genetic possibilities for a single trait are called alleles; two alleles for petal color are purple and white.