Phenotypic trait

A phenotypic trait, simply trait, or character state is any distinct variant of a phenotypic, or observable, characteristic of an organism; it may be either inherited or determined environmentally but typically occurs as a combination of the two. For example, having eye color is a character of an organism, while blue, brown and hazel versions of eye color are traits. The term trait is generally used in genetics, often to describe the phenotypic expression of different combinations of alleles in different individual organisms within a single population, such as the famous purple vs. white flower coloration in Gregor Mendel's pea plants. By contrast, in systematics, the term character state is employed to describe features that represent fixed diagnostic differences among taxa, such as the absence of tails in great apes, relative to other primate groups.

Definition

A phenotypic trait is an obvious, observable, and measurable characteristic of an organism; it is the expression of genes in an observable way. An example of a phenotypic trait is a specific hair color or eye color. Underlying genes, that make up the genotype, determine the hair color, but the hair color observed is the phenotype.

The phenotype is dependent on the genetic make-up of the organism, but is also influenced by the environmental conditions that the organism was subjected to during its ontogenetic development, including various epigenetic processes.

Regardless of the degree of influence of genotype versus environment, the phenotype encompasses all of the characteristics of an organism, including traits at multiple levels of biological organization, ranging from behavior and life history traits (e.g., litter size), through morphology (e.g., body height and composition), physiology (e.g., blood pressure), cellular characteristics (e.g., membrane lipid composition, mitochondrial densities), components of biochemical pathways, and even messenger RNA.

Genetic origin of traits in diploid organisms

Different phenotypic traits are caused by different forms of genes, or alleles, which arise by mutation in a single individual and are passed on to successive generations.