Page "Genotype-phenotype distinction" Paragraph 5

An organism's genotype is a major ( the largest by far for morphology ) influencing factor in the development of its phenotype, but it is not the only one.

Even two organisms with identical genotypes normally differ in their phenotypes.

One experiences this in everyday life with monozygous ( i. e. identical ) twins.

Identical twins share the same genotype, since their genomes are identical ; but they never have the same phenotype, although their phenotypes may be very similar.

This is apparent in the fact that their mothers and close friends can always tell them apart, even though others might not be able to see the subtle differences.

Further, identical twins can be distinguished by their fingerprints, which are never completely identical.