Trait (biological)

A phenotypic trait, or simply trait, is a distinct variant of a phenotypic characteristic of an organism; it may be either inherited or determined environmentally, but typically occurs as a combination of the two. For example, eye color is a character of an organism, while blue, brown and hazel are traits.

A phenotypic trait is an obvious, observable, and measurable trait; it is the expression of genes in an observable way. An example of a phenotypic trait is hair color; underlying genes, which make up the genotype, "control" the hair color, but the actual hair color, the part we see, is the phenotype. Although all aspects of the phenotype are controlled by the genetic make-up of the organism, at least to some extent, they are also influenced by the environmental conditions the organism is subject to across its ontogenetic development, including various epigenetic processes. Regardless of the relative degree of genetic versus environmental control, the phenotype encompasses all of the characteristics of an organism, including traits at multiple levels of biological organization, ranging from behavior and evolutionary history of life 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.

The inheritable unit that may influence a trait is called a gene. A gene is a portion of a chromosome, which is a very long and compacted string of DNA and proteins. An important reference point along a chromosome is the centromere; the distance from a gene to the centromere is referred to as the gene's locus or map location.

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