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PHENOTYPE

Phenotypes are the physical characteristics, such as eye color, displayed by an individual. Phenotype, often used in relation to specific variable characteristics or disease states manifested by an individual, contains no information about the underlying genetic determinants of the characteristics. The genotype contains the genetic information that is used to determine the range of potential phenotypes. Within this range, the environment and other nongenetic factors determine the final phenotype. For example, cystic fibrosis is a phenotype. Conversely, the description of a mutation in the gene that causes this disease is a genotype. The links between genes and particular normal and abnormal phenotypes are being identified using results of the Human Genome Project. Identification of these links is improving child health by providing genetic counselors with detailed information on the causes, phenotypic variability, and environmental factors that lead to birth defects and other diseases. Nongenetic factors influencing a phenotype that results from a particular genotype can be used by genetic counselors to suggest environmental or lifestyle changes that can lessen disease severity.