Rules of Heredity (1850s)

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Austrian monk and botanist Gregor Mendel (1822 – 1884) experimented with more than 28,000 pea plants and discovered how hereditary characteristics, such as height and color, are transmitted from parents to offsprings. He observed how plant’s offspring display recessive and/or dominant characteristics. From these results, he was able to formulate his eponymous laws of heredity, which are very much the foundation of modern genetics. His work was largely rejected and ridiculed during his lifetime; but its true significance was ultimately realized upon its rediscovery sixteen years after his death. Thus, Mendel became known as the “father of genetics.”

Genes Are Transmitted via Chromosomes (1910s – 1920s)

(The 22 autosomes are numbered according to size. The remaining two chromosomes, X and Y, are the sex chromosomes. This above image of the human chromosomes lined up by pairs is called a karyotype.)

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American embryologist and geneticist Thomas Hunt Morgan (1866 – 1945) studied fruit flies for many years by mutating them through physical, chemical, and radiational methods, and then performing crossbreeding tests to find inheritable mutations. Some of the results exhibited Mendelian inheritance patterns, leading him to the conclusion that some traits are sex-linked; and that these traits are probably carried on one of the sex chromosomes (X or Y). Through the use of chromosome recombination, Morgan and his students were able to develop the first genetic map and write the influential book “The Mechanism of Mendelian Heredity” that advanced the “Mendelian-chromosome theory.”

Genes Regulate Biochemical Events (1930s)

(George Beadle)

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American geneticists George Beadle (1903 – 1989) and Edward Tatum (1909 – 1975) exposed neurospora, a type of bread mold, to x-rays; and learned that the resulting mutation causes changes in the production of enzymes responsible for metabolism and synthesis of essential nutrients. These experiments provided evidence that there is a direct link between genes and enzyme reaction, leading them to propose the “one gene-one enzyme” theory.

Tranposons (1940s)

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In her attempt to explain the changing color patterns in maize, American cytogeneticist Barbara McClintock (1902 – 1992) discovered transposons, sometimes referred to as “jumping genes.” Transposons are DNA sections that can jump to different areas within the genome of a single cell; and in due course, cause mutations by either increasing or decreasing the amount of DNA, somehow resulting in diseases that include hemophilia, severe immunodeficiency and predisposition to cancer.

DNA Contains Genetic Information (1920s – 1950s)

(Linus Pauling)

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A number of scientists were able to establish that deoxyribonucleic acid (DNA) is the chemical source of genetic information. Canadian-born American physician and molecular biologist Oswald Avery (1877 – 1955) proved that genes and chromosomes are made up of DNA. American chemist Linus Pauling (1901 – 1994) found that the molecular structure of amino acids and peptides are helical or spiral in shape. Ultimately, Austrian biochemist Erwin Chargaff discovered that certain nitrogen bases in DNA are arranged at a ratio of almost one-to-one, strongly hinting to its base-pair structure.

DNA Is a Double Helix (1950s)

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American molecular biologist James Watson (1928 – ) and English physicist Francis Crick (1916 – 2004) described the molecular structure of DNA, which is made up of two long helical nucleotide strands, each going in opposite direction from the other. The matching base pairs interconnect in the middle of the double helix, maintaining the distance between them. They demonstrated that each strand is a pattern of the other, replicating itself without any structural modification except for occasional errors or mutations.

The Genetic Code (1960s)

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American biochemist Marshall Nirenberg (1927 – ) headed a team that was able to break apart the DNA and discover the genetic code of the amino acid phenylalanine, which contains a sequence of three uracil bases (a form of nucleotide found in RNA). The team went on to determine the nucleotide make-up of more than fifty tri-nucleotides or codons.

Ribonucleic acid (1960s)

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Several scientists detected a chemical in cellular nucleus and cytoplasm that was quite similar to the DNA in structure, called ribonucleic acid (RNA). It has been found to play a key role in protein synthesis, conveyance of genetic information and other essential chemical functions of a cell.

Restriction Enzymes (1950s – 1960s)

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American microbiologists Daniel Nathans (1928 – 1999) and Hamilton Smith (1931 – ), together with Swiss geneticist Werner Arber (1929 – ), discovered restriction enzymes (or restriction endonucleases), which are enzymes that can recognize and cut specific sequences of DNA. Their discovery paved the way to the development of recombinant DNA technology (wherein artificial DNA is engineered through the insertion or combination of DNA to induce or alter a trait for a specific purpose), that made it possible, for instance, the large scale manufacture of human insulin for diabetics using E. coli bacteria.

RNA Splicing (1970s)

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Several groups of scientists discovered the process of RNA splicing. The DNA is first copied or transcribed to produce complementary pre-messenger RNA molecules, which carry the necessary genetic instruction for a cell to synthesize protein. For still unknown reasons, the pre-messenger RNA strands are then spliced or modified to generate mature messenger RNA (mRNA). Errors in the RNA splicing process due to gene mutations or improperly spliced RNA molecules can cause the production of altered proteins that result in diseases.

DNA Fingerprinting (1980s)

(The first DNA fingerprint.)

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British geneticist Alec Jeffreys (1950 – ) found that some DNA sequences are unique to each individual after studying x-rays of DNA samples taken from a friend’s family. Upon realizing the impact of his discovery, he invented and developed DNA fingerprinting (now called DNA profiling) that exploits dissimilarities in the genetic code to identify individuals, leading the birth of DNA forensics. The first forensic application of his technique was to hunt down the rapist and murderer of two teenage girls, Lynda Mann and Dawn Ashworth, who were killed in 1983 and 1986 respectively. The suspect, Colin Pitchfork, was identified and found guilty of murder after DNA samples taken from him matched with the semen samples taken from the two dead girls. The method has also proven helpful in resolving paternity and immigration disputes.

RNA Interference (1990s)

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In their investigation into the regulation of muscle protein production, American molecular biologists Craig Mello (1960 – ) and Andrew Fire (1959 – ) learned that some small sections of double-stranded RNA (dsRNA), which perfectly matches the sequences of a given gene, can inhibit the expression of that gene in a mechanism known as RNA interference (RNAi). Many scientists believe that the discovery has wide-ranging applications, especially in the field of medicine and biotechnology, expressing the hope that drugs can be formulated to induce RNAi with the purpose of inhibiting the expression of disease-causing genes.

Humans Have Around 25,000 Genes (2000s)

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The Human Genome Project was an international research program tasked to sequence the human DNA and identify all human genes. It has discovered and identified approximately 25,000 genes, which was far less than the majority of scientists have estimated. The true understanding of the human genome will hopefully lead to advances in medicine and biotechnology, eventually leading to cures for critical illnesses as cancer, cystic fibrosis and Alzheimer’s disease.

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