phenotype

phenotype Pheno derives from the Greek for display: the phenotype is the manifestation of the genetic make-up of the individual.

‘Old Blue Eyes’ was the name given by many to Frank Sinatra. Having blue eyes is a trait that was part of his phenotype and is genetically determined, dependent on the genetic material derived from both parents. Of course a person's parents do not necessarily both have the same coloured eyes, and an individual may receive eye colour genes specifying different colours from their mother and father. In this situation one gene has dominance over the other gene, which is said to be recessive. Recessive genes can of course be passed on to progeny, and may be expressed in the next generation if dominance is not present.

Eye colour and hair colour are simple traits, but much more complex traits, such as general body form and appearance, result from the complex interplay of many genes derived from both parents. Many children grown up to look very like their mother or father, while most resemble neither very closely because of the considerable mix of the genetic material. Nuture is also able to modify the phenotype — for example, someone with the genetic make-up to express an obese phenotype would not do so if malnourished.

Some diseases that have a genetic basis give rise to unusual phenotypes. For example, children born with cystic fibrosis have inherited an abnormal gene from both parents that results in inappropriate secretions in many hollow organs, such as the lungs, intestine, gall bladder, or pancreas. This abnormal phenotype is usually not expressed by either of the parents, each of whom has one normal gene which is dominant and one abnormal gene which is recessive. The child receiving a set of two abnormal genes, one from each parent, will express these and show the abnormal phenotype.

Alan W. Cuthbert

phenotype Physical characteristics of an organism resulting from heredity. Phenotype is distinct from genotype, since not all aspects of genetic make-up manifest themselves. The phenotype also reflects the interaction of genotype and environment; for instance, a person inheriting a tallness gene may have growth restricted by poor nutrition or cigarette smoke.

phenotype Those observable properties of an organism that are produced by the genotype in conjunction with the environment. Organisms with the same overall genotype may have different phenotypes because of the effects of the environment and of gene interaction. Conversely, organisms may have the same phenotype but different genotypes.