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162 BCE
Galen of Pergamon describes the human body
Galen regarded anatomy as the foundation of medical knowledge, and he frequently dissected and experimented on such lower animals as the Barbary ape (or African monkey), pigs, sheep, and goats. He distinguished seven pairs of cranial nerves, described the valves of the heart, and observed the structural differences between arteries and veins. One of his most important demonstrations was that the arteries carry blood, not air, as had been taught for 400 years. Greek physician and writer. -
1546
Germ Theory of Disease
The germ theory was proposed by Girolamo Fracastoro in 1546, and expanded upon by Marcus von Plenciz in 1762. The germ theory of disease states that many diseases are caused by microorganisms. These small organisms, too small to see without magnification, invade humans, animals, and other living hosts. -
Theory of Inheritance of Acquired Characteristics
If an organism changes during life in order to adapt to its environment, those changes are passed on to its offspring. This is essentially Lamarck's theory. Lamarck believed that giraffes stretched their necks to reach food. Their offspring and later generations inherited the resulting long necks. Lamarck published his theory in 1801. -
The Voyage of the HMS Beagle
H.M.S. Beagle, with a crew of seventy-three men, sailed out of Plymouth harbor under a calm easterly wind and drizzly rain. Charles Darwin was part of this voyage. For five years the Beagle surveyed the coast of South America.The Beagle determined Darwin's whole career, for he was able to explore the continent and islands. He filled dozens of notebooks with careful observations on animals, plants and geology, and collected thousands of specimens, which he crated and sent home for further study. -
Louis Pasteur refutes spontaneous generation
Spontaneous generation refers both to the supposed processes in which different types of life might repeatedly emerge from specific sources other than seeds, eggs or parents. Pasteur's experiment is generally agreed to have decisively refuted the theory of spontaneous generation in 1859. Due to the work of Louis Pasteur and others, that the alternative theory of spontaneous generation had been effectively disproved. -
The Origin of species
On this day, Charles Darwin published his book On the Origin of Species by Means of Natural Selection. It sold out the first time it was published, making it one of the most influential books of modern times. Darwin’s theory argued that organisms gradually evolve through a process he called “natural selection.” Darwin had formulated his theory of natural selection by 1844, but he was wary to reveal his thesis to the public because it so obviously contradicted the biblical account of creation. -
Gregor Mendel publishes works on inheritance of traits in pea plants
Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent. Mendel's Laws of Heredity are usually stated as: 1) The Law of Segregation 2) The Law of Independent Assortment and 3) The Law of Dominance. The genetic experiments Mendel did with pea plants took him eight years (1856-1863) and he published his results in 1865. -
Hardy and Weinberg
The Hardy-Weinberg equation is a mathematical equation that can be used to calculate the genetic variation of a population at equilibrium. In 1908, G. H. Hardy and Wilhelm Weinberg independently described a basic principle of population genetics. This equation states that the amount of genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors. -
T. Hunt Morgan discovers sex-linkage
Morgan noticed one fruit fly with a distinctive characteristic: white eyes instead of red. He isolated this specimen and mated it to an ordinary red-eyed fly. Although the first generation of 1,237 offspring was all red-eyed but for three, white-eyed flies appeared in larger numbers in the second generation. Surprisingly, all white-eyed flies were male. In brief, Morgan had discovered that eye color in Drosophila expressed a sex-linked trait. He received a Nobel Prize in in 1933. -
Neils Bohr develops the Bohr model of atom structure
Bohr diagram, introduced by Niels Bohr and Ernest Rutherford in 1913, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar to structure of the Solar System, but with attraction provided by electrostatic forces rather than gravity. The Bohr model is a relatively primitive model of the hydrogen atom. -
Frederick Griffith describes the process of transformation
He postulated that information could somehow be transferred between different strains of bacteria. This was long before the discovery of DNA and was an inspired piece of scientific detective work. For this study, Griffith used two strains of Pneumococcus bacteria, type III-S and type II-R. Griffith's experiment, was the first experiment suggesting that bacteria are capable of transferring genetic information through a process known as transformation. -
Avery, MacLoed and McCarty determine that DNA is the molecule that carries the genetic code
In 1944, Oswald Avery, Colin MacLeod and Maclyn McCarty helped demonstrate the role of DNA as the carrier of genetic information.As is often the case with such discoveries, Avery's findings were largely unaccepted as evidence for DNA as the hereditary material until separate experiments were performed by other scientists. Thus, eight years later, Alfred Hershey and Martha Chase further confirmed that protein was not the hereditary material -
The Hershey-Chase experiments
Alfred Hershey and Martha Chase wanted to show that proteins carry genetic information. In order to do that, they needed to track the transfer of proteins and DNA between a virus and its host. But after some experiments, they discovered that DNA was the genetic material not protein. In their experiments, Hershey and Chase showed that when bacteriophages, which are composed of DNA and protein, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does not. -
Rosalind Franklin and DNA
In 1962, James Watson, Francis Crick and Maurice Wilkins got the Nobel Prize for the discovery of the shape of DNA. Photo 51 was an X-ray diffraction image that gave them some crucial pieces of information. Only after seeing this photo that Watson and Crick realized that DNA must have a double helical structure. The problem was that Photo 51 was actually made by Rosalind Franklin. Unlike her colleagues, Franklin was not awarded a Nobel Prize for her contributions to this important discovery. -
Watson and Crick propose the double helix model of DNA structure
Cambridge University scientists James D. Watson and Francis H.C. Crick announce that they have determined the double-helix structure of DNA, the molecule containing human genes. In the early 1950s, Watson and Crick were only two of many scientists working on figuring out the structure of DNA. On the morning of February 28, they determined that the structure of DNA was a double-helix polymer, each containing a long chain of monomer nucleotides, wound around each other. -
Plasmodium falciparum is described as the causative agent of malaria
Plasmodium falciparum is a unicelluar protozoan parasite of humans, and the deadliest species of Plasmodium that cause malaria in humans. It is transmitted through the bite of a female Anopheles mosquito. It is responsible for roughly 50% of all malaria cases. It causes the disease's most dangerous form called falciparum malaria. It is therefore regarded as the deadliest parasite in humans, causing a conservative estimate of one million deaths every year. -
Meselson and Stahl work with DNA replication
The Meselson–Stahl experiment is an experiment by Matthew Meselson and Franklin Stahl in 1958 which supported Watson and Crick's hypothesis that DNA replication was semiconservative. In semiconservative replication, when the double stranded DNA helix is replicated, each of the two new double-stranded DNA helices consisted of one strand from the original helix and one newly synthesized. -
Nirenberg cracks the genetic code
Nirenberg, discovered the first "triplet", a sequence of three bases of DNA that codes for one of the twenty amino acids that serve as the building blocks of proteins. Within five years, the entire genetic code was deciphered. In the experiment, an extract from bacterial cells that could make protein even when no intact living cells were present was prepared. Adding an artificial form of RNA, poly-U, to this extract caused it to make a protein composed entirely of the amino acid phenylalanine. -
Endosymbiosis is described by Lynn Margulis
The Endosymbiotic Theory was first proposed by Lynn Margulis in the 1960's. She proposed that the similarities between prokaryotes and organelles, together with their appearance in the fossil record, could best be explained by "endo-symbiosis". Margulis' original hypothesis proposed that aerobic bacteria (that require oxygen) were ingested by anaerobic bacteria (poisoned by oxygen), and may each have had a survival advantage as long as they continued their partnership. -
Apollo 11
It was launched July 16, 1969. It landed on the moon July 20, 1969. Neil A. Armstrong was the commander of the project. Edwin E. Aldrin Jr being the lunar module pilot and Michael Collins command module pilot. As the lunar module lands Armstrong radios "Houston, Tranquility Base here. The Eagle has landed." They left the American flag panted on the moon, as they were the first men from Earth to walk on the moon. (https://www.nasa.gov/mission_pages/apollo/apollo11.html) -
Spliceosomes
In 1977, work by the Sharp and Roberts labs revealed that genes of higher organisms are "split" or present in several distinct segments along the DNA molecule. A spliceosome is a large and complex molecular machine found primarily within the splicing speckles of the cell nucleus of eukaryotic cells. The spliceosome is assembled from snRNAs and protein complexes.Each spliceosome is composed of five small nuclear RNAs (snRNA) and a range of associated protein factors. -
The Sanger Technique is developed
In 1977, Frederick Sanger developed the classical “rapid DNA sequencing” technique, now known as the Sanger method, to determine the order of bases in a strand of DNA. Special enzymes are used to synthesize short pieces of DNA, which end when a selected “terminating” base is added to the stretch of DNA being synthesized. -
Deep sea hydrothermal vents and associated life around them are discovered
Scientists exploring the Galápagos Rift along the mid-ocean ridge in the eastern Pacific noticed a series of temperature spikes in their data. They wondered how deep-ocean temperatures could change so drastically—from near freezing to 750 °F in such a short distance. The scientists had made a fascinating discovery—deep-sea hydrothermal vents. Scientists later realized that bacteria were converting the toxic vent minerals into usable forms of energy through a process called chemosynthesis. -
Kary Mullis develops Polymerase Chain Reaction
Mullis was driving his vehicle late one night with his girlfriend, when he had the idea to use a pair of primers to bracket the desired DNA sequence and to copy it using DNA polymerase; a technique which would allow rapid amplification of a small strand of DNA and become a standard procedure in molecular biology labs. PCR allowed scientists to make millions of copies of a scarce sample of DNA. The technique has revolutionized many aspects of current research. -
CRISPR-Cas9
CRISPR-Cas9 is a unique technology that enables geneticists and medical researchers to edit parts of the genome? by removing, adding or altering sections of the DNA? sequence. The first description of CRISPR was from Osaka University researcher Yoshizumi Ishino in 1987. CRISPR-Cas9, short for clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9. The system has generated a lot of excitement in the scientific community because is faster, cheaper, more accurate. -
Innocence Project
The Innocence Project is a non-profit legal organization that is committed to exonerating wrongly convicted people through the use of DNA testing and to reforming the criminal justice system to prevent future injusticeThe Innocence Project was founded in 1992 by Barry Scheck and Peter Neufeld. The Innocence Project's mission is to free the staggering number of innocent people who remain incarcerated, and to bring reform to the system responsible for their unjust imprisonment. -
Dolly the sheep is cloned
Dolly was part of a series of experiments at The Roslin Institute that were trying to develop a better method for producing genetically modified livestock. Dolly was cloned from a cell taken from the mammary gland of a six-year-old Finn Dorset sheep and an egg cell taken from a Scottish Blackface sheep. Because Dolly’s DNA came from a mammary gland cell, she was named after the country singer Dolly Parton. She was the first mammal to be cloned from an adult cell. -
Sahelanthropus tchadensis
This species is one the oldest known species in the human family tree. Its existence dates back to 7 million years ago in West-Central Africa. The first discovery of this species are nine cranial specimens. The size of the skull shows it had a small brain, and a sloping face like a chimpanzee. (http://humanorigins.si.edu/evidence/human-fossils/species/sahelanthropus-tchadensis) -
The Human Genome
A genome is an organism's complete set of DNA, a chemical compound that contains the genetic instructions needed to develop and direct the activities of every organism. The Human Genome project was an international scientific research project with the goal to determine the sequence of nucleotide base pairs that make up human DNA. It was a 15-year-long project that initiated in 1990. The Human Genome Project was declared complete in April 2003. (https://www.genome.gov) -
Richard L Bible is executed
Arizona’s most notorious death row inmates past and present have interesting stories including Arizona's first use of DNA technology to help in the conviction of Richard Bible. The first use of DNA technology in an Arizona murder case. At trial, in addition to the physical evidence linking Bible to the crime, prosecutors introduced a new technology, DNA analysis, to match the blood found on Bible's shirt to the victim.
