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Gregor Mendel is known as the "Father of Genetics" due to an experiment with pea plants. Mendel resided in an abbey where he was a physics teacher and a gardener. He had a 7-year long pea plant breeding experiment where focused on trait presentation and variation. Through this, he discovered dominant and recessive traits controlled by alleles.
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August Weissman observed and experimented on the sex cells of Hydrozoa. Through these experiments he proposed the idea that “something essential for the species, something which must be carefully preserved and passed on from one generation to another." He called this substance Germ Plasm, and germ plasm was the hereditary substance that all living organisms contain. Although he did not know about DNA many of his ideas are the basis of what we know about genetic material and reproduction.
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Thomas Hunt Morgan is an American biologist who discovered sex-linked genes and a theory of heredity. During an experiment with flies, Morgan observed a mutation, white eyes, being passed down among the flies but only in the males. This led him to formulate the theory of sex-linked characteristics which came from the female X-chromosome. Later, in collaboration with others, he developed the fly experiment into a large scale theory and was able to develop a tool to map it out.
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Frederick Griffith did an experiment on mice in 1928 using fatal and non-fatal strands of pneumonia. Mice infected with a heat-killed fatal virus and alive non-fatal virus separately were ok, but mice infected with both died. He discovered that some chemical or “transforming principle” had transferred from the dead cells to the living cells. He discovered that whatever information was transferring was also able to be passed on to the next generation.
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- Avery, Macleod, and McCarty showed that DNA decided the properties of cells instead of proteins as previously thought. They discovered DNA as the deciding factor while studying a bacteria that can cause pneumonia. Before their work, scientists believed that deoxyribonucleic acid was relatively unimportant. However, they discovered that it was the “transforming principle”
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Erwin Chargaff believed that DNA was more than just simple repeating units. He isolated multiple strands of DNA and measured the amounts of each nitrogen block. He discovered that the amounts of Adenine and Thymine are similar as well as the amounts of Guanine and Cytosine. He was the first to accurately measure the amounts of nucleotides in DNA
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Marie M Daly. was the first African American woman to earn a Ph.D. She is known for her work characterizing histones which is a type of protein that bundles our DNA. During the 1950s nobody really knew what histones were until Daly published her paper in the Journal of General Physiology. She spent hours isolating histones from various animals to determine their properties and composition.
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Rosalind Franklin and Maurice Wilkins were colleagues working on the structure of DNA at King University in London. They used x-ray diffraction in an effort to capture a shadow picture of the DNA’s structure. Using x-ray beams that bounced off the components of the DNA molecule, Rosalind Franklin was able to take an image known as “Exposure 51”. This image revealed the spiral nature of DNA
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Alfred Hershey and Martha Chase conducted an experiment at the Carnegie Institute to confirm that DNA was the building block of genes. They did an experiment with phages and bacteria where a part of the phage would enter the bacteria and replicate itself. Using radioactive isotope labeling the two scientists proved that DNA was made up of nucleic acids separate from proteins. In a final experiment, they furthur proved their findings by demonstrating the movement of DNA in phages and bacteria.
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Watson and Crick discovered the DNA double helix structure based on Rosalind Franklin's “Exposure 51” image. Using Chargriffs rule and figuring out that Adenine paired with Thymine and Cytosine paired with Guanine, they found that these pairs were linked by a hydrogen backbone. They published their paper in Nature and announced to the world that DNA was shaped in a double helix. In 1962 they received the Nobel prize in physiology or medicine.