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A
gene is a molecular unit of
heredity of a living
organism. It is widely accepted by the scientific community as a name given to some stretches of
DNA and
RNA that code for a
polypeptide or for an
RNA chain that has a function in the organism, though there still are controversies about what plays the role of the genetic material. Living beings depend on genes, as they specify all proteins and functional RNA chains. Genes hold the information to build and maintain an organism's
cells and pass genetic
traits to offspring. All organisms have many genes corresponding to various biological traits, some of which are immediately visible, such as
eye color or number of limbs, and some of which are not, such as
blood type, increased risk for specific diseases, or the thousands of basic
biochemical processes that comprise
life.
A modern working definition of a gene is "
a locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions, and or other functional sequence regions ". Colloquial usage of the term
gene (e.g. "good genes", "hair color gene") may actually refer to an
allele: a
gene is the basic instruction—a sequence of nucleic acids (DNA or, in the case of certain
viruses RNA), while an
allele is one variant of that gene. Thus, when the mainstream press refers to "having" a "gene" for a specific trait, this is generally inaccurate. In most cases, all people would have a gene for the trait in question, but certain people will have a specific allele of that gene, which results in the trait variant. Further, genes code for proteins, which might result in identifiable traits, but it is the gene, not the trait, which is inherited.