A trait is a distinct variant of a phenotypic character of an organism that may be inherited, environmentally determined or somewhere in between. For example, eye color is a character or abstraction of an attribute, while blue, brown and hazel are traits.
A trait may be any single feature or quantifiable measurement of an organism. However, the most useful traits for genetic analysis are present in different forms in different individuals.
A visible trait is the final product of many molecular and biochemical processes. In most cases, information starts with DNA traveling to RNA and finally to protein (ultimately affecting organism structure and function). This is the Central Dogma of molecular biology as stated by Francis Crick.
This information flow may also be followed through the cell as it travels from the DNA in the nucleus, to the Cytoplasm, to the Ribosomes and the Endoplasmic Reticulum, and finally to the Golgi Apparatus, which may package the final products for export outside the cell.
Cell products are released into the tissue, and organs of an organism, to finally affect the physiology in a way that produces a trait.
Genetic origin of traits in diploid organisms
The heritable unit that may influence a trait is called a gene. A gene is a portion of a chromosome. An important reference point along a chromosome, which is a very long and compacted string of DNA, is the centromere; the distance from a gene to the centromere is referred to as the gene's locus or map location. A chromosomal region known to control a trait while the responsible gene within not being identified is referred to as a quantitative trait locus.
The nucleus of a diploid cell contains two of each chromosome, with homologous (mostly identical) pairs of chromosomes having the same genes at the same loci.
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