Monday, 19 November 2007

Timeline of Genetics

Since the early 1900s, there has been an incredible explosion of information in the field of genetics. Biologists have unraveled many mysteries, from the workings of the nucleus to how genetics may be used to understand and treat diseases. This timeline illustrates some major landmarks in the history of genetics.

From Mendel to Molecules:A Brief History of Genetics

Charles Darwin publishes The Origin of Species, in which he promotes the theory of natural selection — that members of a population who are better adapted to the environment are more likely to survive and pass on their traits. No theory regarding how traits are passed from generation to generation has been proved true in experiments as of Darwin's time.

Gregor Mendel, an Austrian monk, publishes his findings on the laws of inheritance based on experiments, begun in 1857, with pea plants. His studies are ignored until 1900, well after his death in 1884, but his research lays the foundation for studies of inheritance in the twentieth century and beyond. He is called the "father of genetics."

German biologist Walter Fleming, by staining cells with dyes, discovers rod-shaped bodies he calls "chromosomes."



American biologist Walter Sutton demonstrates that chromosomes exist in pairs that are similar in structure. In light of Mendel's theory that genetic "factors" segregate, he concludes that hereditary factors must lie on chromosomes.
Archibald Garrod discovers the first human disease whose inheritance pattern matches one predicted by Mendel's theories by showing that alkaptonuria, a form of arthritis, is inherited as a recessive trait. The discovery is the first to show how the study of inheritance can benefit the practice of medicine.


The term "genetics" is used for the first time.


Danish botanist Wilhelm Johannsen proposes the term "gene" (from the Greek word "genos" which means "birth") to refer to a Mendelian hereditary factor. Johannsen also proposes two terms, genotype and phenotype, to distinguish between one's genetic make-up and one's outward appearance.

Thomas Hunt Morgan, an American geneticist, publishes The Mechanism of Mendelian Heredity, in which he presents results from experiments with fruit flies that prove genes are lined up along chromosomes. He also describes the principle of "linkage" — that alleles located relatively close to one another on a chromosome tend to be inherited together. By studying the frequency with which traits are inherited together, Morgan and co-workers create a "genetic map" of fruit fly chromosomes showing the relative locations of the genes responsible for dozens of traits, along with approximate distances between them on the chromosome. This work establishes the basis for gene mapping principles still used today.


Oswald Avery, Colin MacLeod, and Maclyn McCarty report evidence that, at least in bacteria, the molecule that carries genetic information is deoxyribonucleic acid (DNA).

Chase and Hershey
The experiments of Martha Chase and Alfred Hershey provide final proof that DNA is the substance that transmits inherited traits from one generation to the next. Hershey receives a Nobel Prize in 1969 for this work.



Francis Crick and James Watson determine that the structure of the DNA molecule is a double helix composed of strings of nucleotides and that two parallel strands formed by sugar and phosphate molecules are joined together by the bonding of specific pairs of nitrogenous bases. The four bases are adenine (A), guanine (G), cytosine (C), and thymine (T). A always pairs with T and C always pairs with G. They share a Nobel Prize for this in 1962.

Joe Hin Tjio determines that the number of chromosomes in humans is 46.(For 30 years, the number was believed to be 48.)

Sydney Brenner, Francois Jacob, and Matthew Meselson identify the role of Ribonucleic Acid (RNA). They determine that messenger RNA (mRNA) is the molecule that carries the genetic information from DNA in the nucleus out into the cytoplasm and that the cell ultimately uses mRNA to make specific proteins.



Marshall Nirenberg and H. Gobind Khorana lead teams that crack the genetic code. They demonstrate that each of 20 amino acids is coded by a sequence of three nucleotide bases (each series of three bases is called a codon).

Fred Sanger develops the chain termination method for sequencing DNA. Many of today's automated DNA sequencers use the principles underlying Sanger's method.

David Botstein and others discover a very useful type of DNA polymorphism, called restriction fragment length polymorphisms (RFLPs). RFLPs are found throughout the genome and are extremely valuable as genetic markers in human genetic studies.

Kary Mullis and others at Cetus Corporation invent a technique for making many copies of a specific DNA sequence: the polymerase chain reaction (PCR). PCR is called the most revolutionary technique in molecular biology in the 1980s. Mullis wins a Nobel Prize for this work.

Chromosome 4
The gene for a human genetic disease is mapped to a specific human chromosome. Study of a large family in Venezuela with Huntington disease reveals that the gene responsible for the disease is on the short arm of chromosome 4. The first genetic test for a disease (Huntington's) was developed based on this finding.

Alec Jeffreys introduces DNA fingerprinting as a method of identification.

The National Center for Human Genome Research is created. It is headed by James Watson and oversees the $3 billion U.S. effort to map and sequence all human DNA.


The Human Genome Project, an international effort to sequence all of the DNA and map all of the genes in humans, is launched.

An international research team, led by Daniel Cohen of the Center for the Study of Human Polymorphisms (CEPH) in Paris, produces a map that includes genetic markers on all 23 human chromosomes. This map is a useful tool for scientists searching for the locations of disease-causing genes.

Allen Roses, MD, and his colleagues at Duke University announce finding a major susceptibility gene for the late-onset form of Alzheimer Disease.


A high-density genetic map of the human genome, consisting of almost 6,000 markers, is published in Science magazine.
Linkage studies identify genes for a variety of conditions including: bipolar disorder, cerulean cataracts, melanoma, hearing loss, dyslexia, thyroid cancer, sudden infant death syndrome, prostate cancer and dwarfism.

The first full genome sequence of a living organism other than a virus is completed for the bacterium Hemophilus influenzae by Craig Venter at Celera. A collaboration of scientists reports sequencing of the complete genome of a complex organism, baker's yeast. The achievement marks the complete sequencing of more than 12 million pairs of DNA.

Dolly and Bonnie
Researchers at Scotland's Roslin Institute report cloning a sheep by transferring a cell nucleus from an adult ewe into an embryonic sheep cell. The result is a sheep named "Dolly."(Pictured at left are Dolly and her first lamb, Bonnie, born in 1999)

A human genetic map is produced, showing the chromosomal locations of markers from more than 30,000 human genes.
Herceptin® (trastuzumab) and Herceptest® are approved in the US for the treatment of a subset of women with breast cancer based on the results of a lab test. This is the first time the US Food and Drug Administration required that a diagnostic lab test kit used to predict patient response be made available for use with a drug.

The SNP Consortium is formed by pharmaceutical, information and technology companies and a charitable trust for the purpose of providing public, unrestricted genomic data about single nucleotide polymorphisms (SNPs), the most common form of genetic variation. The resulting SNP map, which is being updated constantly, is used by scientists to find SNP markers for gene mapping and disease studies.

A rough draft of the human genome is completed and published by the Human Genome Project and Celera. The project was planned to last 15 years, but rapid technological advances accelerated the expected completion date. Project goals are to discover all 30,000 to 40,000 human genes (the human genome) and make them accessible for further study and to determine the complete sequence of the 3 billion DNA bases in the human genome.


A private U.S. research company, Advanced Cell Technology (ACT) announces it has cloned human embryos. The company says the intention is not to create cloned human beings but to make lifesaving therapies for a wide range of human diseases. Political and religious leaders around the world condemn the effort.
Researchers announce that genetic screening for a particular gene can help physicians decide which women are best suited to use the drug tamoxifen (while they are still healthy) to help prevent breast cancer. Other researchers announce that they are exploring the use of genetics to predict which patients are most likely to experience serious adverse reactions from a chemotherapy drug.

50 years of DNA
50th anniversary of the discovery of the double-helix structure of DNA by Francis Crick and James Watson, who received the Nobel Prize for their work in 1962. The Human Genome Project publishes the complete human genetic sequence in the journal Nature (24 April 2003), more than two years ahead of schedule

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