Genetics

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Genetics is that branch of science which 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.

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 they are the information normally carried on DNA. Manipulation of the DNA can in turn alter the inheritance, and features of various organisms. This science which grew out of biochemistry and genetics is widely known as molecular biology.

Timeline:

1859 Charles Darwin publishes The Origin of Species
1865 Gregor Mendel
1903 Chromosomes are discovered to be hereditary units
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
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 DNA is semiconservatively replicated
1961 The genetic code is arranged in triplets
1977 DNA is sequenced
1997 First genome sequenced
2001 Human genome is sequenced by the Human Genome Projects

The study of inherited features not strictly associated with DNA is called epigenetics.

See also : biology -- central dogma of genetics