In
biology, a 'character' is an attribute of an
organism that allows it to be compared with another. In
genetics this refers to
heritable features which can exist in more than one state.
[Lawrence, Eleanor (2005) ''Henderson's Dictionary of Biology''. Pearson, Prentice Hall. ISBN 0-13-127384-1] A 'trait' is a distinct
phenotypic character of an organism that may be inherited, environmentally determined or somewhere in between.
For example,
eye color is a ''character'', while blue, brown and hazel are ''traits''.
Definition
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.
Environmental origin
The environment plays a large role in the determination of traits. This is natural as all organisms must have input (and output) of energy and matter in order to maintain their overall elevated
energy state.
Genetic origin of traits in diploid organisms
The heritable unit that may produce a trait is called a
gene. A gene is a strand of
DNA that is part of a very long and
compacted string of
DNA called a
chromosome. An important reference point along this string 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.
Mendelian expression of genes in diploid organisms
A gene is only a
DNA code sequence; the slightly different variations of that sequence are called alleles.
Alleles can be significantly different and produce different product
RNAs.
Combinations of different
alleles thus go on to generate different traits through the
information flow charted above. For example, if the alleles on homologous
chromosomes exhibit a "simple dominance" relationship, the trait of the "dominant" allele shows in the phenotype.
Gregor Mendel pioneered modern genetics. His most famous analyses were based on clear-cut traits with simple dominance. He determined that the
heritable units, what he called "
genes", occurred in pairs and could exhibit
linkage. His tool was
statistics: long before the molecular model of
DNA was introduced by
James D. Watson and
Francis Crick.
Some examples of Inherited genes include eye color.
Biochemistry of dominance and extensions to expression of traits
The
biochemistry of the intermediate
proteins determines how they interact in the cell. Therefore, biochemistry
predicts how combinations of different alleles will produce varying traits.
Extended expression patterns seen in diploid organisms include facets of
incomplete dominance,
codominance, and
multiple alleles.
See also
★
Character displacement
★
Skill
References
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