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The theory of Natural Selection
Charles Darwin challenged the idea that a higher being created life. Propose Life changes over time through natural selection -
Gregor Mendel
Through his work on pea plants (Pisum sativum) discovered that traits were passed on from parents through “factors”. Mendel established the basic principles of inheritance, namely the principles of dominance, independent assortment and segregation. His meticulous studies mark the birth of modern genetics. -
Friedrich Miescher
Miescher discovered DNA itself through his studying of white blood cells when after the experiment there’s was snotty gray stuff of biological substance he called nuclein (now nucleic acids) but didn’t know it’s role or what it look like. -
Discover of chromosomes and mitosis
Walther Fleming (1843-1905) observes little structures inside cell's core that separate during animal cell division. He calls it chromosomes. He stains chromosomes to observe them clearly and describes the whole process of mitosis in 1882. -
Chromosome Theory of Inheritance
Walter Sutton observes that the segregation of chromosomes during meiosis matched the segregation pattern of Mendel’s. So genes are located inside chromosomes. -
First use of the word GENE
Wilhelm Johannsen coins the word “gene” to describe the Mendelian unit of heredity. He also uses the terms genotype and phenotype to differentiate between the genetic traits of an individual and its outward appearance. -
Thomas Hunt Morgan: relation between genes and chromosomes
http://www.raiscuola.rai.it/articoli/thomas-hunt-morgan-la-teoria-cromosomica-dellereditariet%C3%A0-storia-della-scienza/7251/default.aspx Thomas Morgan’s experiments in 1910 with the fruit fly (Drosophila melanogaster) revealed the existence of the sex chromosomes. -
Frederick Griffith: genetic transformation on bacteria
Griffith's studies on Streptococcus pneumoniae: during transformation's process the donor bacterium moves cellular materials to a receiving one and new properties are acquired. -
Oswald Avery: DNA is the transformation's factor
Avery's studies on Streptococcus pneumoniae: he demonstrates that the bacterial strain treated with DNase enzyme aren't transformed. So DNA is the transformation's factor. -
Linkage
J.H. Muller understands that the genome can be modified by mutant factors (X rays, UV rays, chemical products, ...). By crossing mutants of Drosophila, he discovers the LINKAGE, a group of genes located inside the same chromosome and inhrerited together. An exception in represented by the crossing over process that separates the linkage. -
Erwin Chargaff's ratio
Chargaff discovers that the amount of adenine is equal to thymine and the same for cytosine and guanine. So a pyrimidines pair always with a purines. But he fails DNA structure because he describes DNA as symmetrical.
https://dnalc.cshl.edu/resources/3d/21-chargaff-ratios.html
https://dnalc.cshl.edu/resources/3d/25-basepairing.html -
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DNA is the hereditary material
Hershey and Chase studies on T2 bacteriophage: this virus duplicates inside bacteria by injecting only its DNA. So DNA represents hereditary material transmitted to new generations. -
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Copying Enzymes
Arthur Kornberg and his group seperated DNA polymerase. DNA polymersase is an enzyme used for all kinds of DNA techniques and sequencing. They first seperated DNA polymerase from E. coli bacteria. He did this by adding protein to a tube of salt solution holding DNA molecules and nucleotide building blocks, it was able to make new strands of DNA. -
Meselson and Stahl discover DNA replication process
DNA replication process is semi conservative: from the beginning DNA molecule origin two DNA molecules, each one composed by one old strand and one new strand.
https://www.youtube.com/watch?v=JcUQ_TZCG0w -
"A gene, a polypeptide"
Beadle and Tatum, thanks to experiments on Neurospora fungi, demonstrate that there is a linkage between genes and proteins expression. So, in a living organism, the phenotype is determined by the genotype.
https://dnalc.cshl.edu/resources/3d/central-dogma.html -
Okazaki fragments
Reiji and Tsuneko Okazaki discover that the two strands of DNA are replicated in different ways. So they distinguish a lagging strand from a leading strand. While the leading strand undergoes a continuous replication process, the lagging one is synthesized discontinuously by producing DNA fragments called Okazaki fragments.
