Biology
From Mendel to CRISPR
Follow how life moved from observation and classification to cells, evolution, genes, and genomes.
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1856–1863
Mendel conducts controlled pea-crossing experiments
Gregor Mendel
Across planned crosses of pea varieties, Mendel counted traits over generations and inferred discrete hereditary factors.
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1866
Mendel publishes Experiments on Plant Hybrids
Gregor Mendel
Mendel's paper documented repeatable ratios and an account of inheritance based on discrete units.
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1900
Mendel's inheritance work is independently rediscovered
Hugo de Vries · Carl Correns · Erich von Tschermak
Three botanists reported inheritance results that brought Mendel's 1866 paper back into active scientific debate.
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1902
Sutton and Boveri connect Mendelian factors to chromosomes
Walter Sutton · Theodor Boveri
Sutton and Boveri independently argued that chromosome behavior during meiosis could explain Mendelian segregation.
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1910
Morgan demonstrates sex-linked inheritance in fruit flies
Thomas Hunt Morgan
A white-eye mutation in Drosophila followed the inheritance of the X chromosome, tying a specific trait to a chromosome.
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1913
Sturtevant maps genes by recombination frequency
Alfred Sturtevant
Sturtevant used crossover frequencies to infer the linear order and relative spacing of genes on a chromosome.
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1928
Griffith discovers bacterial transformation
Frederick Griffith
Griffith found that material from heat-killed disease-causing bacteria could turn harmless bacteria into a disease-causing form that passed the change to subsequent generations.
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1944
Avery, MacLeod, and McCarty identify DNA as the transforming principle
Oswald Avery · Colin MacLeod · Maclyn McCarty
Purified bacterial fractions showed that transformation depended on DNA and survived treatments that destroyed protein or RNA.
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1952
Hershey and Chase track DNA into infected bacteria
Alfred Hershey · Martha Chase
Radioactive labels showed that bacteriophage DNA, rather than most phage protein, entered bacteria during infection.
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1950
Chargaff establishes base-composition regularities
Erwin Chargaff
Measurements across species showed that DNA base proportions vary by organism while adenine matches thymine and guanine matches cytosine.
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1952
Franklin and Gosling obtain decisive DNA diffraction evidence
Rosalind Franklin · Raymond Gosling
High-quality X-ray diffraction of the B form of DNA revealed a helical pattern and precise structural dimensions.
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1953
A double-helix model explains DNA structure and copying
James Watson · Francis Crick · Rosalind Franklin · Raymond Gosling · Maurice Wilkins · Erwin Chargaff
Watson and Crick built a complementary double-helix model using chemical constraints and X-ray evidence produced at King's College, including Franklin and Gosling's work.
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1958
Meselson and Stahl demonstrate semiconservative DNA replication
Matthew Meselson · Franklin Stahl
Heavy-nitrogen labeling and density-gradient centrifugation showed that each daughter DNA molecule contains one old and one new strand.
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1961
Short-lived messenger RNA links genes to ribosomes
Sydney Brenner · François Jacob · Matthew Meselson · François Gros · Walter Gilbert
Experiments identified unstable RNA copies that carry genetic information from DNA to protein-making ribosomes.
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1961
Nirenberg and Matthaei decode the first codon
Marshall Nirenberg · Heinrich Matthaei
A cell-free system translated synthetic poly-U RNA into polyphenylalanine, identifying UUU as a codon for phenylalanine.
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1966
The genetic code is substantially completed
Marshall Nirenberg · Har Gobind Khorana · Robert Holley · Heinrich Matthaei
Complementary cell-free, synthetic-RNA, and transfer-RNA studies assigned the codons and clarified how they direct protein synthesis.
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1972
Berg's group constructs recombinant DNA molecules
Paul Berg · David Jackson · Robert Symons
The group joined DNA from different biological sources into a single recombinant molecule in vitro.
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1977
Chain-termination sequencing makes DNA readable
Frederick Sanger · Steven Nicklen · Alan Coulson
Sanger and colleagues published a chain-termination method that determines nucleotide order through terminated DNA fragments.
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1985
PCR makes selected DNA sequences rapidly amplifiable
Kary Mullis · Cetus Corporation
The polymerase chain reaction used repeated cycles and primers to copy a chosen DNA segment exponentially.
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1990
The Human Genome Project officially begins
International Human Genome Sequencing Consortium · National Institutes of Health · U.S. Department of Energy
An international program began to map and sequence the human genome while developing technology, model-organism resources, and ethics research.
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2000
A working draft of the human genome is announced
International Human Genome Sequencing Consortium
The public consortium announced assembly of a working draft covering most of the human genome sequence.
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2003
The Human Genome Project announces completion
International Human Genome Sequencing Consortium
The international consortium announced a high-quality reference covering the gene-rich portion of the human genome within the project's technical limits.
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2007
Experiments show CRISPR provides adaptive bacterial immunity
Rodolphe Barrangou · Philippe Horvath · Danisco research team
Changing CRISPR spacer content changed bacterial resistance to matching bacteriophages, demonstrating an adaptive immune function.
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2012
Cas9 is programmed with guide RNA to cut chosen DNA
Emmanuelle Charpentier · Jennifer Doudna · Martin Jinek · Krzysztof Chylinski · Ines Fonfara · Michael Hauer
A simplified Cas9 system used a designed guide RNA to cut DNA at a chosen sequence in vitro.
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2013
CRISPR-Cas9 edits genes in mammalian cells
Feng Zhang · George Church · Le Cong · Prashant Mali · independent research teams
Independent groups rapidly adapted CRISPR-Cas9 to target and alter genes in cultured mammalian cells.
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