<P> One's genotype differs subtly from one's genomic sequence, 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, and the combination of alleles the individual carries (see homozygous, heterozygous). Genotypes are often denoted with letters, for example Bb, where B stands for one allele and b for another . </P> <P> Somatic mutations which 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 . </P> <P> 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 . </P> <P> Any given gene will usually cause an observable change in an organism, known as the phenotype . The terms genotype and phenotype are distinct for at least two reasons: </P>

The genetic makeup of a trait can be illustrated by its