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Gregor Mendel
Gregor Mendel was an Austrian monk whose experiments with pea plants formed the basis of heredity in 1866. He tracked the passing of genetic traits to offspring, and concluded that some traits were recessive to dominant traits. He also discovered that it was possible for a plant to carry both a dominant and recessive gene, and that either of these genes can be passed to offspring during reproduction. Mendel's work on heritable traits gave rise to the eventual discovery of chromosomes and DNA. -
Friedrich Miescher
In 1869, Friedrich Miescher was trying to determine the composition of white blood cells. To do this, Miescher collected used bandages from clinics and extracted the cells from pus. He isolated a new molecule from the nucleus of these cells, which he called nuclein, and discovered that there was a special ratio of phosphorus to nitrogen within all nuclein. Miescher's work paved the way for the discovery of individual nucleic acids and contributed to our understanding of the structure of DNA. -
Walter Sutton
In 1902, Walter Sutton declared that chromosomes were distinct separate entities to each other; distinct morphological individuals. He worked with a species of grasshopper that had large cells and clearly visible chromosomes, and concluded that chromosomes duplicate and divide but always remain as a whole distinct structure. His work was published at the same time as Theodor Boveri who also worked on chromosomes, and they are usually grouped together in the Sutton-Boveri Chromosome Hypothesis. -
Theodor Boveri
In 1902, Theodor Boveri discovered that a complete set of chromosomes is required for normal development of offspring. This he concluded after removing some chromosomes from fertilised sea urchin eggs and finding that they did not grow. He deduced that all chromosomes must be different to each other, in order for this to occur. His work was published at the same time as Walter Sutton who also worked on chromosomes, and they are usually grouped together in the Sutton-Boveri Chromosome Hypothesis. -
Thomas Morgan
In 1910, Thomas Morgan discovered sex-linkage by conducting breeding experiments with drosophila fruit flies. He observed that some males had white eyes, while others had red. From Mendel's observations, he gathered that the white eyes trait was recessive, which is why it occurred less in the female population. With this information, he proved that some traits are sex-linked, as males only need one copy of the recessive gene to express the trait. His work led to the discovery of sex chromosomes. -
Phoebus Levene
Levene is mostly known for his incorrect tetranucleotide theory of four nitrogenous bases arranged around a phosphate backbone. However, his work did contribute to our understanding of DNA structure. Levene discovered the sugar ribose in what we know as RNA, and 20 years later discovered a similar sugar in DNA, noting that is was missing an oxygen atom. He called it deoxyribose. He also discovered the relationship between phosphates, sugars, and nucleic acids, and coined the term 'nucleotides'. -
Erwin Chargaff
Erwin Chargaff's work on DNA led to many revelations about its structure and how it links with genetics. Through the use of chromatography, he deduced that DNA taken from different species is different, which supported the theory that DNA is genetic material. In 1949, he discovered that the ratio of Adenine to Thymine in DNA is 1:1, as is the ratio between Guanine and Cytosine. This, he discovered through several experiments, was the same for the DNA of any species. -
Linus Pauling
In 1951, Linus Pauling proposed that DNA was a triple-helix connected by a single phosphate backbone, with the nucleotides facing outwards. Chemically, this was impossible, as nucleotides have a negative charge and would repel each other being attached closely to the phosphate. However, his model helped scientists James Watson and Francis Crick to develop their own, successful model of DNA. -
James Watson and Francis Crick
In 1953, James Watson and Francis Crick produced the first accurate 3D model of DNA, with the help of data accumulated from Rosalind Franklin and Maurice Wilkins. Before the contribution of these other scientists, Watson and Crick made several mostly incorrect models of DNA, and with the knowledge of DNA as a double-helix were able to alter their model into one that we still use today. -
Rosalind Franklin
In 1953, Rosalind Franklin used X-ray diffraction to discover that the DNA molecule is shaped as a double-helix with its nitrogenous bases lining up along the middle of the molecule to form 'rungs' similar to those of a ladder. Her photographs of the DNA molecule led to the creation of the famous Watson & Crick model of DNA we often see today. Before any credit for this discovery was attributed to Franklin, she died of ovarian cancer as a result of X-ray exposure that arose from her work. -
Maurice Wilkins
In 1953, Maurice Wilkins shared the photos of Rosalind Franklin's DNA findings with James Watson without her consent. These photographs showed DNA had a double-helix structure with 'rungs', similar to a twisted ladder. Wilkins' collaboration with Watson and Crick led him to be awarded the Nobel Prize in 1962 for the famous Watson and Crick model of DNA that we often see today. Without this collaboration, the DNA model proposed by Watson and Crick would not have been correct.
