The existence of genes was first suggested by Gregor Mendel (1822–1884),
who, in the 1860s, studied inheritance in peaplants (''Pisum sativum'') and
hypothesized a factor that conveys traits from parent to offspring.
He spent over 10 years of his life on one experiment. Although he did
not use the term ''gene'', he explained his results in terms of inherited
characteristics.
Prior to Mendel's work, the dominant theory of heredity was one of
blending inheritance, which proposes that the traits of the parents blend or
mix in a smooth, continuous gradient in the offspring.
Although Mendel's work was largely unrecognized after its first
publication in 1866, it was rediscovered in 1900 by three European scientists,
Hugo de Vries, Carl Correns, and Erich von Tschermak, who had reached similar
conclusions from their own research. However, these scientists were not yet
aware of the identity of the 'discrete units' on which genetic material resides.
Mendel was also the first to hypothesize independent assortment, the
distinction between dominant and recessive traits, the distinction between a
heterozygote and homozygote, and the difference between what would later be
described as genotype (the genetic material of an organism) and phenotype (the
visible traits of that organism).
Mendel's concept was given a name by Hugo de Vries in 1889, who, at that
time probably unaware of Mendel's work, in his book ''Intracellular
Pangenesis'' coined the term "pangen" for "the smallest particle
one hereditary characteristic".
Darwin used the term Gemmule to describe a microscopic unit of
inheritance, and what would later become known as Chromosomes had been observed
separating out during cell division by Wilhelm Hofmeister as early as 1848.
The idea that chromosomes are the carriers of inheritance was expressed
in 1883 by Wilhelm Roux. The modern conception of the gene originated with work
by Gregor Mendel, a 19th-century Augustinian monk who systematically studied
heredity in pea plants.
Mendel's work was the first to illustrate particulate inheritance, or
the theory that inherited traits are passed from one generation to the next in
discrete units that interact in well-defined ways.
Danish botanist Wilhelm Johannsen coined the word "gene"
("gen" in Danish and German) in 1909 to describe these fundamental
physical and functional units of heredity, while the related word genetics was
first used by William Bateson in 1905.
The word pangenesis is made from the Greek words ''pan'' (a prefix
meaning "whole", "encompassing") and ''genesis''
("birth") or ''genos'' ("origin").
In the early 1900s, Mendel's work received renewed attention from
scientists. In 1910, Thomas Hunt Morgan showed that genes reside on specific
chromosomes. He later showed that genes occupy specific locations on the
chromosome.
With this knowledge, Morgan and his students began the first chromosomal
map of the fruit fly ''Drosophila''. In 1928, Frederick Griffith showed that
genes could be transferred.
In what is now known as Griffith's experiment, injections into a mouse
of a deadly strain of bacteria that had been heat-killed transferred genetic
information to a safe strain of the same bacteria, killing the mouse.
A series of subsequent discoveries led to the realization decades later
that chromosomes within cells are the carriers of genetic material, and that
they are made of DNA (deoxyribonucleic acid), a polymeric molecule found in all
cells on which the 'discrete units' of Mendelian inheritance are encoded.
In 1941, George Wells Beadle and Edward Lawrie Tatum showed that
mutations in genes caused errors in specific steps in metabolic pathways. This
showed that specific genes code for specific proteins, leading to the "one
gene" hypothesis.
In 1953, James D. Watson and Francis Crick demonstrated the molecular
structure of DNA. Together, these discoveries established the central dogma of
molecular biology, which states that proteins are translated from RNA which is transcribed
from DNA. This dogma has since been shown to have exceptions, such as reverse
transcription in retroviruses.
In 1972, Walter Fiers and his team at the Laboratory of Molecular
Biology of the University of Ghent (Ghent, Belgium) were the first to determine
the sequence of a gene: the gene for Bacteriophage MS2 coat protein. Richard J.
Roberts and Phillip Sharp discovered in 1977 that genes can be split into
segments.
This led to the idea that one gene can make several proteins. Recently
(as of 2003–2006), biological results let the notion of gene appear more
slippery. In particular, genes do not seem to sit side by side on DNA like
discrete beads.
Instead, regions of the DNA producing distinct proteins may overlap, so
that the idea emerges that "genes are one long continuum". Following
the sequencing of the human genome and other genomes, it has been found that
rather few genes (~20 000 in human, mouse and fly, ~13 000 in roundworm, >46
000 in rice) encode all the proteins in an organism.
These protein-coding sequences make up 1–2% of the human genome. A large
part of the genome is transcribed however, to introns, retrotransposons and
seemingly a large array of noncoding RNAs.
Genetic and genomic nomenclature
Gene nomenclature has been established by the HUGO Gene Nomenclature
Committee (HGNC) for each known human gene in the form of an approved gene name
and symbol (short-form abbreviation).
All approved symbols are stored in the
[http://www.genenames.org/cgi-bin/hgnc_search.pl] HGNC Database. Each symbol is
unique and each gene is only given one approved gene symbol.
This also facilitates electronic data retrieval from publications. In
preference each symbol maintains parallel construction in different members of
a gene family and can be used in other species, especially the mouse.
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