•He found that when a yellow pea plant and a green pea plant were bred together their offspring was always yellow. However, in the next generation of plants, the green peas returned in a ratio of 3:1.

Using available X-ray data and model building, they were able to solve the puzzle that had baffled scientists for decades. They published the now-famous paper in Nature in April, 1953 and in 1962 they were awarded the Nobel Prize for Physiology or Medicine along with Maurice Wilkins.

Cytogenetics first had a major impact on disease diagnosis in 1959, when an additional copy of chromosome 21 was linked to Down's syndrome. In the late 1960s and early 70s, stains such as Giemsa were introduced, which bind to chromosomes in a non-uniform fashion, creating bands of light and dark areas. The invention transformed the discipline, making it possible to identify individual chromosomes, as well as sections within chromosomes, and formed the basis of early clinical genetic diagnosis.

The following few years were taken up with experiments, as Nirenberg tried to show that RNA could trigger protein synthesis. By 1960, Nirenberg and his post-doctoral fellow, Heinrich Matthaei were well on the way to solving the coding problem.

They named the gene they identified, which was located on chromosome 17, BRCA1. However, it was clear that not all breast cancer families were linked to BRCA1, and, with continued research, a second gene BRCA2 was located on chromosome 13.

Everyone has 2 copies of both BRCA1 and BRCA2, which are tumour suppressor genes. If a person has 1 altered copy of either gene it can lead to an accumulation of mutations, which can then lead to tumour formation.

Many organisations had a long-standing interest in mapping the human genome for the sake of advancing medicine, but also for purposes such as the detection of mutations that nuclear radiation might cause.

The project's goals included: mapping the human genome and determining all 3.2 billion letters in it, mapping and sequencing the genomes of other organisms, if it would be useful to the study of biology, developing technology for the purpose of analysing DNA and studying the social, ethical and legal implications of genome research.

Known as H.flu, Haemophilus Influenzae is a bacterium that can cause meningitis and ear and respiratory infections in children. Prior to this breakthrough, scientists had only managed to sequence the genome of a few viruses, which are around ten times shorter than that of H.flu.

The project took around a year and was a remarkable achievement. Its success proved that the random shotgun technique could be applied to whole genomes quickly and accurately, paving the way for future discoveries.

Known as the 'Bermuda Principles', the agreement was designed to ensure that sequence information led as rapidly as possible to advances in healthcare and research.

In order to co-ordinate the process, it was also agreed that large-scale sequencing centres would inform the Human Genome Organisation (HUGO) of any intentions to sequence particular regions of the genome. HUGO would then place this information on their website and direct visitors to the specific centres for more detailed information regarding the current status of sequencing.

At the time, the sequence was the longest continuous stretch of DNA ever deciphered and assembled. However, it was only the first deciphered chapter of the human genetic instruction book - the rest was still to come.

During their research, the scientists discovered that every fruit fly cell contains 13,601 genes, making it by far the most complex organism decoded at the time. However, by contrast, human cells contain 70,000 genes. Whilst the Human Genome Project still had a long way to go to achieve its ultimate objective, this was an important milestone along the way.

Amazingly, it emerged that 90% of the mouse's genome could be aligned with the corresponding regions on the human genome. Both the mouse and human genome also contained around 30,000 protein-coding genes. These discoveries highlighted for the first time just how closely mammalian species were genetically related.

Scientists had achieved a high-quality sequence of the entire human genome. In 2001, the Human Genome Project had published a 'rough draft' of the human genome, which included a 90% sequence of all three billion base pairs.

Before this discovery, it was believed that monozygotic twins are 100% genetically identical, and that DNA testing could not be used in criminal or paternity cases involving identical twins, as it was impossible to tell them apart.