The study of the process of heredity, by which characteristics are passed from parents to offspring, so that organisms resemble their recent ancestors, is genetics. The modern theory of genetics is based on the discovery that heredity is controlled by discrete factors called genes. Advances in chemistry since the 1930s have made it possible to analyse the molecular structure of genes, so that genetics has become part of the realm where biology and chemistry meet, in otherwords the chemistry of life, or technically molecular biology. Genes can be regarded as units of biological information.
The origin of genetics is usually traced back to the work of Gregor Mendel & & & & (1822 - 1884) and a paper he published in 1866, which reported the results of a series of experiments on varieties of garden pea, carried out over the preceding ten years, in which he investigated inheritance of traits such as height, flower colour and shape of seeds. From these he was able to formulate some basic laws of heredity.
However the significance of Mendel's work was not appreciated in his lifetime, and it was only in 1900 that other researchers, Hugo De Vries & & & & & H (1848 - 1935), Carl Correns & (1864 - 1933) and Erich von Tschermak-Seysenegg & & (1871 - 1962), conceived similar experiments and rediscovered Mendel's paper. There are sceptic & views of this history however.
It was observed around 1902/3 by Walter S. Sutton & & (1877 - 1916) and Theodor Boveri & (1862 - 1915) that in higher organisms transmission of the cell-components known as chromosomes during cell division and reproduction paralleled the behavior of the hereditary factors. The term 'genetics' was introduced by William Bateson & & & H (1861 - 1926) in 1905, and the term 'gene' for the hereditary factors was proposed by Wilhelm Johanssen (1857 - 1927) in 1909. Thus the genes were carried by the chromosomes.
Thomas Hunt Morgan & & & (1866 - 1945) and members of his research team at Columbia University in New York, Calvin Bridges (1889 - 1938), Alfred H. Sturtevant & (1891 - 1970) and Hermann J. Muller & & & (1890 - 1967), happened in 1910 upon the fruit fly Drosophila melanogaster that proved ideally suited to Mendelian breeding experiments, and enabled them to develop methods from 1911 to 1929 for mapping gene positions on chromosomes. Muller 1927 found that X-rays could induce mutations in genes.
By 1920 it had become clear that chromosomes contain two biological compounds, proteins which were large molecules made up of long polymers of amino acids, and deoxyribo nucleic acid, called DNA for short, which was however mistakenly thought to be a compound of fixed composition, consisting of the four bases adenine, cytosine, guanine, and thymine (A, C, G and T). Since genes had to be of variable composition to account for varied heredity it was thought they were made of protein. The four-base theory of DNA structure was overthrown in 1934 when Torbjorn Caspersson (1910 - 1997) proved that DNA is a macromolecule.
Frederick Griffith & (1879 - 1941), a London medical officer, in 1928 conducted experiments on mice with the pneumonia-causing bacterium Streptococcus pneumoniae and showed that genetic material from a heat-killed virulent strain could transform a harmless strain into a virulent strain. Oswald Avery (1877 - 1955) beginning to research such bacteria in 1932, eventually showed in 1944, with colleagues Colin Macleod (1909 - 1972) and Maclyn McCarty (1911 - 2005), that the active agent is DNA. However their conclusion was not widely accepted until confirmed by later work on bacteriophages.
Max Delbrück & & (1906 - 1981) who began as a student of quantum chemistry and nuclear physics investigated, with N. W. Timofeyev-Ressovsky (1900 - 1981) and Karl G. Zimmer (1911 - 1988), the molecular nature of the gene (1935) and after moving to the USA in 1937 set up the 'Phage Group', which included Salvador Luria (1912 - 1991) and Alfred Hershey (1908 - 1997). These researchers used the infection cycle of viruses that attack bacteria (known as bacteriophages) as an experimental system to investigate what genes are and how they work.
Erwin Chargaff (1905 - 2002) and colleagues used new chromatographic techniques to demonstrate 1945-50 that the base-ratios in DNA are constant, A = T and G = C. Maurice Wilkins (1916 - 2004) and Rosalind Franklin (1920-1958) at King's College, London, obtained X-ray diffraction patterns from crystallised DNA. These facts formed part of the information that Francis Crick & & & H (1916 - 2004), and James Watson & & & & & (1928 - ) collated, that enabled them to identify the double-helix structure of DNA in 1953.
The helix structure of DNA is rather like a twisted ladder formed of two polymer strands whose monomers are a combination of a sugar with a phosphate, the rungs of the ladder being pairs of bases, either A-T or G-C, linked by weak hydrogen bonds.
The above is only a brief historical introduction. I hope to expand this page further.
Meanwhile the following are sources available on the internet.
Basic Principles of Genetics
History of Genetics
Landmarks in the History of Genetics
Genetics and Genomics Timeline (X)
Opposition to Bateson
What is a Genome?
Genome Biology: On Gene Autonomy
Timeline of the History of Genetics
The Birth of Modern Genetics
How Genetics Got a Chemical Education
DNA and Molecular Genetics
Linus Pauling and the Race for DNA
Crick and Watson Profile
The Human Genome Project
New Scientist: Articles on Genetics
My main sources of information on Genetics and its history have been:
T. A. Brown Genetics: A Molecular Approach Chapman and Hall, London 1992 (second edition).
Peter Tallack (editor), The Science Book Cassell & Co, London 2001.