Introduction » up to 1900 » 1901 to 1953 » 1954 to 1982 » 1983 to 2008

This is a timeline of major events in the science of genomics: the science of DNA encoding and how genes work. Part 2 begins from genetic science at the “Fly Lab” inspired by the theory Mendelian inheritance and concludes with the discovery of the double helix model of DNA.

1900 to 1920: The Physical Gene

1902: British physician Archibald Garrod identifies the first human genetic disease.

Garrod was investigating a rare disease called alkaptonuria when he realized that the disease must be passed genetically in families. This insight suggested to Garrod that many other rare diseases could be understood by inheritance.

1903: American Graduate student Walter Sutton discovers the mechanism of meiosis while studying the sperm cells of grasshoppers and proposes that heredity factors are located in chromosomes.

This was Sutton’s last work in genetics literature. Why? Sutton never finished his PhD. Instead, he earned his M.D. and became a surgeon. Thinking of going ABD to pursue more practical employment? See 100 Years Ago: Walter Sutton and the Chromosome Theory of Heredity if you feel guilty about not feeling guilty enough.

1904: German biologist Theodor Boveri concludes that a full set of chromosomes is necessary for the normal development of sea urchin embryos. This discovery, together with Walter Sutton’s proposal, will form the basis for the Sutton-Boveri chromosome theory of inheritance: that chromosomes are the carriers of hereditary units.

The Sutton-Boveri chromosome theory states that Medelian alleles (genetic material) are located on chromosomes. In 1904, this theory was not yet well supported by evidence, and many scientists considered “genes” (see 1906, Bateson) to be only an artificial abstraction for explaining experimental results.

1905: Danish botanist Wilhelm Johannsen uses the terms “genotype” and “phenotype” to explain how plants that are genetically identical may have different physical characteristics.

Specifically, Johannsen realized that selective breeding between plants with a single self-fertilized ancestor is ineffective because all the descendant plants are genetically identical. Yet these plants, despite having identical genes, were not physically identical. Therefore, the characteristics of an organisms must be the product of both its genes (genotype) and its environment (realized expression of genes, or phenotype.)

1906: British biologist William Bateson coins the word “genetics” for the study of how physical, biochemical, and behavioral traits are transmitted from parent to offspring.

As a boy, Bateson was described as “vague and aimless.” He only began to shine intellectually when at St. John’s College he was encouraged to study biology. As an adult, Bateson was known as an iconoclast. His early career suffered due to his unpopular ideas, yet his intellectually tenacity and independence led him to appreciate Mendel’s theory of inheritance —despite the dismissal of his peers. Bateson’s propensity for intellectual risk was soon rewarded by a successful academic career and the credit for founding a new scientific field: genetics.

1908: British mathematician Godfrey H. Hardy and British geneticist Wilhelm Weinberg independently formulate the Hardy-Weinberg principle which mathematically related the frequencies of genotypes to the frequencies of alleles in randomly mating populations.

An allele is a genetic unit that that occupies a specific position on a specific chromosome. Diploid cells (most mammal cells) have two alleles per gene, and depending on which two alleles are present, the gene is expressed in a different way. These alleles can be dominant (always expressed) or recessive (only expressed in pairs). The Hardy-Weinberg principle states that the proportion of dominant and recessive genes tends to remain constant between generations of an infinitely large, closed, randomly mating population. This is important because it means that even though recessive genes may not be expressed, the genetic information is not destroyed. Given this, predictions can be made regarding the probabilities of inheriting a trait given the distributions of that trait in a population.

Ironically, Hardy reveled in “pure mathematics” and openly slurred “applied mathematics,” yet this applied mathematical contribution is partially named in his honor.

1908: An entire frog is made radioactive and placed on a photographic plate, thus creating the first and likely most hilarious biological autoradiograph.

X-ray technology was used in genomics from inducing mutations (see 1915) to discovering the double-helix structure of DNA (see 1953), but mostly, I just think it’s funny.

1909: Danish botanist and geneticist Wilhelm Johannsen coins the word “gene” for the units of inheritance inside chromosomes.

That is, sets of alleles “implement” genes, and a gene is trait that is expressed differently depending on the set of alleles that implement it.

1910: American pathologist Francis Peyton Rous shows that when pieces of chicken tumor (sarcoma) are screened through a fine filter and the cell-free filtrate is injected into other chickens, they also develop sarcomas.

What Rous discovered was that cancer can be caused by viruses. That is, somehow viruses manipulated the genetic material of animal cells. Interestingly, Rous (then 31) didn’t actually use the term “virus” in his original research for fear of offending his senior colleagues. Yet, despite the potential for political difficulties early in his career, Rous did persist with his work and won the Nobel Prize for physiology in 1966.

1910: American geneticist Thomas Hunt Morgan discovers the concept of sex-linked inheritance for eye color in studies with fruit flies. This proved the Sutton-Boveri chromosome theory (see 1904) which states that genes are physical entities located on chromosomes.

Morgan discovered that while both male and female fruit flies could carry the recessive gene for white eyes, only males expressed the trait. Thus, Morgan deduced that the gene must be carried on the X chromosome and not on the Y chromosome. That is, specific genes are carried on specific chromosomes. Morgan’s work also led to the theory of allele linkage: that alleles for genes are physically connected in chromosomes and thus tend to be inherited together. This studying the eye color of fruit flies proved fortuitous, because fruit flies only have 4 chromosomes, and such an easily observable trait (eye color) was linked to another easily observable trait (sex) which happened to be determined by a different set of chromosomes (XX for female, XY for male).

Morgan established the scientifically prodigious and notably egalitarian “fly lab” at Columbia University with his American geneticist colleagues and students, as evident from this and the flurry of discoveries attributed to his American colleagues noted below.

1911: Gene mapping (chromosome mapping) is developed by American geneticist Alfred H. Sturtevant.

Given the discovery that genes were physical entities mapped onto chromosomes, the next natural question seemed to be “where are the genes on the chromosomes?” A student under Morgan, Sturtevant theorized that genes closer to each other tended to stay together and genes further apart tended to separate during crossing-over in meiosis which mixes alleles between pairs of chromosomes to make egg and sperm gametes. By observing how likely alleles on a chromosome were inherited together, one could estimate their relative positions.

1915: American geneticist Hermann Muller begins experiments using X-rays to induce mutations.

Muller imagined the gene as the origin of life and fundamental mechanism of evolution. Thus, that environmental factors such as X-rays could damage or change genes unpredictably alarmed Muller, particularly as atomic science advanced and nuclear technologies proliferated. In 1926, Muller published that x-rays induce mutations which earned him the Nobel Prize for physiology or medicine in 1946.

Notably, Muller described the ultimate objective of his genetic work to be “the control of the evolution of man by man himself.” After the Great Depression in the USA on 1929, Muller became a socialist “sympathizer” and left for Germany, but the rise of Nazism compelled him to leave again to the Soviet Union in 1933. However, political forces again threatened Muller, this time because proponents of Lamarckism, a competing (and now debunked) theory that evolution is driven by traits acquired or modified through the use or disuse of body parts, won the official political support of Stalin. Muller denounced Russian communism and returned to the United States where he continued to campaign against the apocalyptic dangers of nuclear weapons. Yet, Muller was still politically and sometimes even physically threatened for his heretical political views including his support for benevolent eugenics programs and sperm banks.

We like to think of ourselves as more enlightened today than in the early 20th century and that modern science is somehow more pure and less susceptible to political fashions. Yet, considering James Watson’s (see 1953, Watson and Crick) recent roast and subsequent ad-hominium accusations of “racism” in 2008, this sadly is not true. Political correctness should be independent of scientific correctness.

“There is no firm reason to anticipate that the intellectual capacities of peoples geographically separated in their evolution should prove to have evolved identically. Our wanting to reserve equal powers of reason as some universal heritage of humanity will not be enough to make it so.” —James Watson

Also, see Race, genes, and intelligence by William Satetan at Slate Magazine.

1915: Thomas Hunt Morgan, Alfred Sturtevant, Hermann Muller, and Calvin Bridges publish The Mechanism of Mendelian Heredity, a textbook compiling the genetic advances and techniques of the Fly Lab group and all genetic science to date.

Unlike a scientific discovery, it may be difficult to judge the significance of contributions to scientific education. Yet, fine textbooks like The Mechanism of Mendelian Heredity must have inspired, instructed, and influenced innumerable scientists and potential scientists to perform better, more significant work. A writing a great scientific textbook may not be sensational, but it’s important, and I feel that great books should be noted as scientific achievements like other discoveries and inventions.

1916: Thomas Hunt Morgan creates the first chromosome map (gene map) for the four chromosomes of the fruit fly.

This chromosome map is the applied conclusion of the gene mapping technique as noted previously (see 1911, Sturtevant).

1920 to 1953: DNA, the Double Helix Molecule

1928: British medical officer Frederick Griffith discovers genetic transformation of a bacterium. Griffith’s hypothesized “transforming principle” was later discovered to be DNA.

While working on a pneumonia vaccine after World War 1, Griffith’s Experiment showed that a non-living “transforming principle” in a heat-killed deadly strain of bacteria could transform a similar but non-fatal strain of the bacteria into the deadly strain. Griffith died in an air raid clutching a page of formulas which have never been interpreted.

The idea of genetic transformation makes the idea that abuse of antibiotics can and has created drug-resistant strains of bacteria which can transfer their resistances to other, perhaps much more dangerous strains of bacteria. You can purchase your very own antibiotic hand washing pandemic kit at a local Walgreen’s or other fine commercial venues of convenience near you.

1928: Louis J. Stadler shows that ultraviolet radiation can cause mutations.

That is, sunlight can cause mutations. Wear sunscreen.

1929: Russian-American biochemist Phoebus A. Levene discovers the sugar 2-deoxyribose, the five-carbon sugar in DNA.

1933: German physicist Ernst Ruska invents the electron microscope.

The science of the electron microscope itself are beyond the scope of this genomics timeline. Nonetheless, it’s included here as its superior resolution and magnification were critical to the investigation of cells and organic molecules.

1940: American geneticist George W. Beadle and American biochemist Edward L. Tatum establish the “one gene, one enzyme” hypothesis. In 1941, they demonstrate this theory while working with bread mold mutated by X-rays.

Beadle and Tatum were able to create single-gene mutations in bread molds which correlated to abnormal substance accumulations or new vitamin requirements as particular bread mold enzymes encoded by that gene were disabled. Modern research has revised this hypothesis to the more general “one gene — one polypeptide” (a sequence of amino acids, a part of a protein).

1944: American microbiologists Oswald T. Avery, Colin M. MacLeod, and Maclyn McCarthy demonstrate the role of DNA in genetic inheritance and identify it as as the “transforming agent” from the Griffith’s Experiment (see 1928, Griffith).

Before this discovery and even well into the next decade, the focus of biochemistry was almost entirely on proteins. DNA molecules were thought to be of little importance, perhaps as noted by McCarthy, some sort of stringy structural brace for cells. Genes were thought to be encoded by the 20 amino acids which compose proteins in cells. Fortunately, Griffith’s “transforming principle” hypothesis seized the attention of another researcher also striving for a cure for pneumonia, Oswald Avery, one of the founding fathers of immunochemistry and of renown meticulousness. Working with pounds of extremely virulent pnuemonia germs, Avery and his colleagues patiently eliminated “transforming agent” candidate substances, including proteins, until his focus narrowed to DNA.

Avery’s research took about ten years and he was over 65 until he could prove that DNA was the heredity agent of life. Unfortunately, his work was not universally appreciated until after his death, and Avery never received the Nobel Prize. Ironically, Avery initially dismissed Griffith’s work as sloppy until several other scientists confirmed transmissible heredity changes in his field immunology.

1945: Italian-American microbiologist Salvador E. Luria and American microbiologist Alfred D. Hershey demonstrate that viruses can mutate.

Hershey and Luria independently discovered that phages (bacterial viruses) must spontaneously mutate, rather than only gradually, as the prevailing genetic theory claimed. Hershey also discovered in 1946 that when different strains of phages infected the same bacterium, the viruses could exchange genetic material. Hershey’s work with phages led the creation of the scientifically prolific and self-declared “phage group,” a group of researchers of which James Watson (see 1953, Watson and Crick) became a member.

1948: American molecular biologist Alfred Mirsky discovers RNA in chromosomes.

RNA is a nucleic acid like DNA which aids in protein synthesis. At this time, the function of RNA is unknown.

1950: American geneticist Barbara McClintock publishes her discovery of transposons—mobile genetic elements, in corn.

McClintock was originally a post-doc at Cornell, but as Ivy-League Cornell only appointed women professors in the department of home economics until 1947 (only 60 year ago, also, “department of home economics?”), she left for the new genetics department at the University of Missouri and then left again for the Carnegie Institute’s Cold Spring Harbor Laboratory in New York.

Transposons themselves are DNA sequences which can move from one place in a DNA sequence to another, inducing mutations as they move.

1950: Austrian-American biochemist Erwin Chargaff establishes the pairings A (adenine) <=> T (thymine) and G (guanine) <=> C (cytosine) in DNA.

Chargaff discovered that pyrimidines (cytosine and thymine) and purines (adenine and guanine) always exist in equal proportions in all organisms. Further, Chargaff hypothesized that the different number of proportions and many possible sequences of these nucleic bases were of sufficient complexity to encode genes. His discoveries convinced Watson and Crick (see 1953) that these bases must be molecularly bonded and thus Chargaff’s discoveries were instrumental to the double helix model of DNA.

1950: Alfred D. Hershey shows that phages consist only of DNA surrounded by a protein shell by analysis with an electron microscope.

This discovery gave further weight to the theory that DNA encoded and transmitted the genetic information of life, not some other more molecularly complex protein as commonly believed.

1952: New Zealand-British biophysicist Maurice Wilkins and British x-ray crystallographer Rosalind Franklin use X-ray diffraction to study DNA. They show that DNA is coiled and has a spiral form with the sugar-phosphate backbone on the outside.

Wilkins participated in the Manhattan Project in Berkeley, California and the invention of the hydrogen bomb. The bomb spurred Wilkins to a moral crisis, causing him to lose interest in physics and begin study of biology. Particularly, the idea of a highly complex molecule which encoded all of life as hypothesized in fellow physicist Erwin Schrodinger’s book “What is Life” inspired Wilkins.

Wilkins, with the help of Raymond Gosling and Rosalind Franklin, use x-ray diffraction imagery to discover the first evidence of the “regular pattern” in DNA molecules which he hypothesized from microscope observations.

Rosalind Franklin’s contributions to the discovery of the eventual double helix model discovery are of moderate controversy. She clashed personally with Wilkins, Watson, and eventually with her superior’s, John Randall’s, injunction to abandon the DNA problem entirely. Watson described her in his autobiograph, “The Double Helix” as the key obstacle to Watson’s and Crick’s research. Nonetheless, Franklin did produce the X-ray diffraction pictures that led Watson and Crick to discover the double helix model of DNA. Unfortunately, Franklin died of cancer in 1958 at age 38 and never had the chance to defend her record nor was eligible to earn the Nobel Prize for her contributions. To her credit, Franklin was working on a draft in which she proposed a double-chain helical structure of DNA when she learned of the more complete (and published) Watson-Crick model. Further, Franklin’s difficulties may be partially attributed to the discrimination of women and minorities prevalent at this time in American history.

1952: Alfred D. Hershey and American laboratory assistant Martha Chase use radioactive tracers to show that the DNA, not the protein, from bacteriophageT2 is the genetic material that infects bacteria.

Specifically, tracers showed that DNA contains the element phosphorous but no sulfur, but the protein from the phage had sulfur but no phosphorous. Thus, when these radioactive-tracer phages were allowed to infect bacteria and the radioactive phage protein was stripped away, the radioactive phage DNA was found to be inside the bacteria cells. When this tracer-infected bacteria was cultivated, it produced a new generation of phages. This was yet more evidence that the DNA molecule was both responsible for communicating and transmitting genetic information to create life.

1953: American geneticist James Watson and British Biophysicist Francis Crick propose the double helix model of DNA.

The double helix model of DNA has two sugar-phosphate strands which wind around each other with pairs nucleotide bases pointing inward. From this model, the understanding of the function and encoding of DNA could begin.

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