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Genetics

Genetics is that branch of science that relates to the study of genes, and
their role in biological inheritance. This is the process by which offspring
tend to have features similar to their parents. The earliest applications of
genetics were developed long before the beginning of recorded history, with
the domestication and selective breeding of plants and animals. The genetic
information is chemically encoded in DNA (deoxyribose nucleic acid).
Genomics is the study of all the DNA in a given species.

It wasn't until 1865 that Gregor Mendel first traced inheritance patterns of
certain traits in pea plants and showed that they obeyed simple statistical
rules. Although not all features show this Mendelian inheritance, his work
acted as a proof that application of statistics to inheritance could be
highly useful. Since that time many more complex forms of inheritance have
been demonstrated. From his statistical analysis Mendel defined a concept
that he described as an allele which was the fundamental unit of heredity.
The term allele as Mendel used it is nearly synonymous with the term gene,
whilst the term allele now means a specific example of a particular gene.
The significance of Mendel's work was not understood until early in the
twentieth century, after his death, when his research was re-discovered by
other scientists working on similar problems.

Mendel was unaware of the physical nature of the gene. We now know that
genetic information is normally carried on DNA. (Certain viruses store their
genetic information in RNA). Manipulation of DNA can in turn alter the
inheritance, and features of various organisms.

These genes, in turn, contain the information to produce proteins, which
then ultimately bring about changes in the phenotype of the organism.

Some view that life can be defined, in molecular terms, as the set of
strategies which RNA polynucleotides have used and continue to use to
perpetuate themselves. This definition is based on the RNA world hypothesis.

The science which grew out of the union of biochemistry and genetics is
widely known as molecular biology.

Changing the DNA of an organism for a practical end is called genetic engineering.

Timeline:

     1859 Charles Darwin publishes The Origin of Species
     1865 Gregor Mendel's paper, Experiments on Plant Hybridization
     1903 Chromosomes are discovered to be hereditary units
     1905 British biologist William Bateson coins the term "genetics" in a
     letter to Adam Sedgwick
     1910 Chromosomes include genes
     1913 Gene maps show chromosomes containing linear arranged genes
     1927 Physical changes in genes are called mutations
     1928 Frederick Griffith discoveres a hereditary molecule that is
     transmissible between bacteria (see Griffiths experiment)
     1931 Crossing over is the cause of recombination
     1944 Oswald Theodore Avery, Colin McLeod and Maclyn McCarty isolate DNA
     as the genetic material (at that time called transforming principle)
     1945 Genes code for proteins; see the original central dogma of
     genetics
     1950 Erwin Chargaff shows that the four nucleotides are not present in
     nucleic acids in stable proportions, but that some general rules appear
     to hold (e.g., that the amount of adenine, A, tends to be equal to that
     of thymine, T).
     1952 The Hershey-Chase experiment proves the genetic information of
     phages (and all other organisms) to be DNA
     1953 DNA structure is resolved to be a double helix by James Watson and
     Francis Crick
     1958 The Meselson-Stahl experiment demonstrates that DNA is
     semiconservatively replicated
     1961 The genetic code is arranged in triplets
     1977 DNA is sequenced
     1997 First genome sequenced
     2001 First draft sequences of the human genome are released
     simultaneously by the Human Genome Project and Celera Genomics.

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