Genotype & Phenotype Correlation

The Genotype and Phenotype Correlation Explained

Whereas the genotype of a person is the set of alleles that make up his or her genetic constitution, either collectively at all loci or, more typically, at a single locus; the phenotype is the observable expression of a genotype as a morphological, clinical, cellular, or biochemical trait.

Genotype also can refer to the alleles at a specific genetic locus. Phenotype can also be defined as the effect of gene action, whether caused by a single gene or the entire genotype.

The phenotype is usually thought of as the presence or absence of a disease, but phenotype can refer to any manifestation, including characteristics that can be detected only by blood or tissue testing.

In addition, the meaning of genotype and phenotype may be illustrated by a musical analogy.

The musical notation contains all of the necessary information or instructions for the notes to be played by each instrument and temporal relationships of the various parts—this is the genotype.

The phenotype is the sound we hear, which is strongly influenced by the environment, including the soloist, the conductor, the orchestra, and the hall in which it is performed, or the quality of the recording.

A phenotype may, of course, be either normal or abnormal in a given individual, but in genetic mapping studies, which emphasizes disorders of medical significance, the focus is on abnormal phenotypes—that is, genetic disorders.

Although each gene usually encodes a polypeptide chain or RNA molecule, a single abnormal gene or gene pair often produces multiple diverse phenotypic effects and determines which organ systems are involved, which particular signs and symptoms occur, and when they occur.

Under these circumstances, the expression of the gene defect is said to be pleiotropic. At present, for many pleiotropic disorders, the connection between the gene defect and the various manifestations is neither obvious nor well understood.