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Mendel
Mendel worked with pea plants. He took the "P" generation and crossed those together. He then examined the F1 generation, and breeded those to create the F2 generation. After all of these tests, he came to a few conclusions. He noticed that some genes were "linked" which came to be known as gene linkage. His main discovery was the gene, which he called a unit of hereditary info that determines a character. This layed the foundation for future DNA scientists as this helped them find more. -
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Genetics
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Griffith
Griffith wanted to prove that DNA can "transform". He took the Spanish Influenza virus and had two strains: the harmful S strain with a capsule, and harmless R strain with no capsule. He then injected heat-killed S strain with no capsule and the mice lived. Eventually, he found out that harmless R strain mixed with heat-killed S strain transfomed into a capsule S strain. His experiment showed the fact that DNA can transform, which helped scientists in the future figure out where DNA came from. -
Avery
Avery basically did the exact same experiment as Frederick Griffith. At this point, people knew about meiosis and how it worked. They knew chromosomes were made out of DNA and protein. Avery removed the protein from the S strain of the Spanish influenza, which ultimately led to the DNA enzymes being affected. This led to the next discovery in DNA by -
Chargaff
In 1950, Erwin Chargaff figured out how nucleotides pair up along the backbone of the DNA. He figured out that adenine goes with thymine, and cytosine goes with guanine. The percentages for each pair are almost identical. He also figured out that the purine: pyrimidine ratio is 1:1 for every base pair. This helped scientists further investigate into the shape of DNA, and that the base pairings help put where the other parts of the nucleotide go in the DNA. -
Franklin
Franklin is known for her diffracting of X-ray on DNA to determine structure of it, She did dangerous work, and it ultimately led to her dying of ovarian cancer at age 38. Crystallography was what helped her figure out the shape of DNA. Sadly, she died before she could publish anything about her work. It wasn't until 1953 that Watson and Crick finished up her discoveries. -
Hershey and Chase
They wanted to find out which macromolecule held the genes: was it DNA or protein? They put a virus on a bacteriophage and let the virus insert its genes into the cell, and it eventually lysed. The virus then got out into other cells. They put two groups to allow infection, and the ultimately put both groups in a centrifuge and separated the protein and DNA. This helped them figure out that the DNA holds the genes. This paved the way for other scientists to figure out other aspects of DNA. -
Watson and Crick
Watson and Crick basically left off where Rosalind Franklin left off; trying to find what shape DNA was actually in. They eventually found out that it was in a double helix shape, which goes exactly with Franklin's evidence and Chargaff's rules of the base pairings. After Watson and Crick did their research, they did give a nod to Franklin, but not enough credit that she actually deserved. -
Meselson and Stahl
They wanted to find out how DNA replicated, and in which manner. They grew bacteria in normal nitrogen, and in heavy nitrogen. They spun the two different ones in a centrifuge and found DNA in different places. Then, they had the heavierbacteria transfer to the normal and did not replicate in there. They took it out and saw that the DNA was in the middle. This says that DNA replication is semi-conservative, which means that the old DNA splits and forms with new DNA. Half old, half new. -
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