Courtesy Armed Forces Institute of Pathology, Washington, DC

Gregor Mendel

Heredity

Experiments with peas lead Austrian monk Gregor Mendel to discover that certain traits are inherited in varying proportions, depending on whether they are recessive or dominant.

1869

Frederich Miescher

First DNA Isolation

Swiss physician Frederich Miescher isolates DNA from cells. Miescher calls it "nuclein." Later, it becomes known as nucleic acid.

1909

Wilhelm Johannsen

The Term "Gene" is Coined

German scientist Wilhelm Johannsen names the Mendelian unit of heredity "gene," from the Greek word, "give birth to."

1928

Frederick Griffith, Jr.

Gene Transformation Suggested

British microbiologist Frederick Griffith's experiments with pneumococcus prove that a "transforming principle" allows genes to transfer from one bacterium to another.

1944

Oswald Avery, Colin MacLeod, and Maclyn McCarty

DNA Transforms Cells

American geneticists Oswald Avery, Colin MacLeod, and Maclyn McCarty prove that DNA is the "transforming principle"—the vehicle for passing hereditary information through generations.

1950

Erwin Chargaff

Chargaff's Rule

Austrian-American biochemist Erwin Chargaff discovers equal amounts of adenine and thymine, and cytosine and guanine, a distinctive pattern of base-pairing regularities in DNA. In 1950 he publishes his findings.

1952

Alfred D. Hershey and Martha Chase

Genes are Made of DNA

American geneticists Alfred Hershey and Martha Chase demonstrate that only the DNA of a virus needs to enter a bacterium to infect it, proving that genes are made of DNA.

1959

Arthur Kornberg and Severo Ochoa

Polymerase and RNA Identified

American biochemist Arthur Kornberg and Spanish born biochemist Severo Ochoa share the Nobel Prize in Physiology or Medicine for their discovery of polymerases in the biologic synthesis of deoxyribonucleic acid and ribonucleic acid.

1961

Sydney Brenner, François Jacob, and Matthew Meselson

Cellular Messengers: mRNA

South African chemist Sydney Brenner, French biologist François Jacob, and American geneticist Matthew Meselson show that short-lived RNA molecules, which they called messenger RNA (mRNA), carry the genetic instructions from DNA to structures in the cell called ribosomes, (the site of protein synthesis).

1962

James D. Watson and Frances H. Crick

DNA structure is a double helix

In 1953, James Watson and Frances Crick propose a three-dimensional model for the structure of DNA: a double helix molecule formed by two chains, each composed of alternating sugar and phosphate groups, connected by nitrogenous bases. Watson and Crick (with British biophysicist Maurice Wilkins) are awarded the 1962 Nobel Prize in Medicine or Physiology.

1978

Werner Arber and Hamilton Smith

Role of Restriction Enzymes

Swiss molecular biologist Werner Arber shows how specialized enzymes can cut DNA into short strands. These enzymes are subsequently dubbed "restriction enzymes." In 1970, American molecular biologist Hamilton Smith and colleagues determine that restriction enzymes can cut DNA molecules at precise and predictable locations. Arber shares the 1978 Nobel Prize in Medicine or Physiology with Smith and American biologist Daniel Nathans.

1980

Frederick Sanger, Alan Coulson, Alan Maxam, and Walter Gilbert

DNA Sequencing Methods Developed

In the 1960s and 1970s, British scientists Frederick Sanger and Alan Coulson, and Alan Maxam and Walter Gilbert in the United States, develop DNA sequencing techniques. Automated equipment makes DNA sequencing a speedy, routine laboratory procedure. Gilbert and Sanger win the 1980 Nobel Prize in Chemistry for their work.

David Botstein, Ronald W. Davis, Mark Skolnick, and Ray White

Restriction-Fragment-Length Polymorphism (RFLP) proposed

American geneticist David Botstein, biochemist Ronald W. Davis, population geneticist Mark Skolnick, and biologist Ray White publish a paper on their theory that restriction fragment-length-polymorphisms (RFLPs) can be used to produce a linkage map of the human genome and to map the genes that cause disease in humans.

1984

Alec Jeffreys

Variable Numbers of Tandem Repeats

British geneticist Alec Jeffreys finds that multiple copies of short nucleotide sequences, 3 to 30 base pairs long, are repeated one after another, 20 to 100 times [e.g., GACTGACTGACT]. These groups of repeat sequences, called minisatellites or VNTRs (variable number of tandem repeats), are now known to be widely scattered throughout the human genome. The number of these regions at different loci are different in each individual.

1991

Alec Jeffreys

Short Tandem Repeats in DNA Analysis

Geneticist Alec Jeffreys develops short tandem repeat (STR) DNA typing, which the forensic community adopts as its standard.

British geneticist Alec Jeffreys began working in 1977 on a technique that could identify individuals through samples of their DNA. In 1984, he and colleagues devised a way to use a newly discovered property of DNA, isolated areas of great variability between individuals called restriction fragment length polymorphisms (RFLP), for forensic identification—the original DNA fingerprint.

In 1986, police asked Jeffreys for help in finding a man who had raped and killed two girls. DNA tests exonerated the primary suspect. Through a genetic dragnet, police found the perpetrator, Colin Pitchfork, who gave himself away when he asked a friend for a substitute blood sample.

Within a year, genetic fingerprinting was making the unique molecular structures of victims and suspects visible in criminal investigations around the world. Today, RFLP-based DNA analysis is being supplanted by newer techniques of genetic identification.

Courtesy University of Leicester

Courtesy Magnum Photos

1702

Richard Mead

First Publication on Poisons

Richard Mead's A Mechanical Account of Poisons in Several Essays is the first book in English devoted entirely to the discussion of poisons.

1752

First Chemical Tests in a Trial

The Mary Blandy case in England is the first reported use of chemical tests to detect arsenic in a legal trial.

1814

Mathieu Orfila

First Toxicology Publication

In France, Mathieu Orfila's Traité des Poisons is the first book devoted entirely to the subject of toxicology. Orfila popularizes the word "toxicology."

1836

James Marsh

Marsh Test Devised

English chemist James Marsh devises a test for identifying trace amounts of arsenic.

1851

Jean-Servais Stas

Alkaloid Poison Test Developed

Belgian chemist Jean-Servais Stas develops a method for detecting vegetable alkaloid poisons (caffeine, quinine, morphine, strychnine, atropine, opium) in dead bodies.

1860

Robert Wilhelm Eberhard Bunsen and Gustav Robert Kirchhoff

Spectrum Analysis Developed

With the aid of the spectroscope, which they invented in 1859, German chemist Robert Bunsen and physicist Gustav Kirchhoff discover that vaporizing a substance creates a unique "signature" spectrum, which can be used to identify it. Using the spectroscope, in 1860, Bunsen and Kirchhoff discover two new alkali metals—cesium and rubidium.

1906

Mikhail Tswett

Paper Chromatography Developed

Italian-born Russian botanist Mikhail Tswett invents paper chromatography, initially to study the make-up of plant proteins such as chlorophyll.

1926

Theodor Svedberg

Ultracentrifuge Developed

Swedish chemist Theodor Svedberg builds the first ultracentrifuge—a machine that separates particles by mass—making it possible to determine precisely the molecular weights of highly complex proteins. Svedberg wins the Nobel Prize for Chemistry in 1926 for his invention of the ultracentrifuge and studies in the chemistry of colloids.

1941

Arnold Beckman, Howard Cary and Warren Baxter at National Technical Laboratories (now Beckman Coulter)

Ultraviolet Spectrophotometer Introduced

The Beckman model DU spectrophotometer is the first instrument to probe the ultraviolet region with high precision and accuracy. According to Bruce Merrifield, Nobel Laureate in chemistry, the DU is "probably the most important instrument ever developed in the advancement of bioscience."

1948

Arne Tiselius

Electrophoresis and Adsorption Developed

During the 1920s and 1930s, Swedish chemist Arne Tiselius helps develop and improve electrophoresis and analysis by adsorption. In 1948, he receives the Nobel Prize in Chemistry for his work.

1950s

New Technologies Incorporated

Ultraviolet and infrared spectrometry, X-ray diffraction, and paper chromatography are applied to forensic science.

1952

Richard L. M. Synge and Archer J. P. Martin

Partition Chromatography Developed

British biochemists Archer J. P. Martin and Richard L. M. Synge demonstrate partition chromatography to the Biochemical Society at a 1941 meeting in London. They share the Nobel Prize in Chemistry in 1952 for their development of partition chromatography.

1953

Gas Chromatography Developed

The first commercial gas chromatograph is manufactured.

1966

New Technologies Incorporated

Fourier-transformed infrared spectroscopy (FTIR), a technique that measures various infrared wavelengths, and atomic absorption spectroscopy, which uses the absorption of light to measure the concentration of gas-phase atoms, are invented.

"I got a hit…and it took the wind out of my lungs. It was a real homicide…The patients had died a terrible death."

—Brian Andresen, Ph.D., American forensic chemist, 2004

In 1998 a respiratory therapist at a Glendale, California hospital told police that he had ended the lives of 50 patients. Efren Saldivar stated that he had deliberately overdosed patients with pancuronium bromide (Pavulon) or succinylcholine chloride. But, when he recanted his confession, police were forced to release him for lack of evidence.

Experts then referred detectives to the Lawrence Livermore National Laboratory's Forensic Science Center, sometimes called the "lab of last resort." There, Dr. Brian Andresen said Pavulon might still be detectable in the victims' bodies. If so, police could prove that murder had been committed.

1901

Wilhelm Conrad Röntgen

X-ray Discovered

German physicist Wilhelm Röntgen, working with a cathode ray tube in his laboratory, in 1895, discovers "a new kind of ray that can travel great distances, penetrate solid matter, activate fluorescent screens, and expose photographic plates." He receives the first Nobel Prize in Physics in 1901 for his work in discovering the X-ray.

1942

Karl Theodore Dussik

Ultrasound First Applied to Medicine

Austrian physiatrist Karl Theodore Dussik publishes a paper on the medical application of ultrasonics in his investigation of the brain. While important to diagnostic medicine, ultrasonics has few applications to forensics.

1952

Felix Block and Edward Purcell

Nuclear Magnetic Resonance (NMR) Developed

Working independently, during the 1940s, Swiss-born physicist Felix Block at Stanford University and American physicist Edward Purcell at Harvard University find that atomic nuclei placed in a magnetic field absorb energy in the range of the spectrum. The nuclei re-emit this energy when they are transferred to their original state. Block and Purcell share the 1952 Nobel Prize in Physics for this work.

When applied to human subjects, the term (NMR) technology becomes known as "magnetic resonance imaging."

1973

Michael E. Phelps and Edward J. Hoffman

PET Scan Developed

American scientists Michael E. Phelps and Edward J. Hoffman develop position emission tomography (PET) scans, a nuclear medicine medical imaging technique which maps the functional processes of the body. The technology is important to diagnostic medicine, but has little application to forensics.

1979

Godfrey N. Hounsfield and Allan M. Cormack

Computed Tomography Developed

During the 1960s, South African-born physicist Allan Cormack of Tufts University and British engineer Godfrey Hounsfield of EMI Laboratories in England contribute separately to the development of computer-assisted tomography. They share the 1979 Nobel Prize in Physiology or Medicine.

2003

Paul C. Lauterbur and Peter Mansfield

Magnetic Resonance Imaging (MRI) Developed

During the 1970s, American chemist Paul Lauterbur and British physicist Peter Mansfield made pioneering contributions which led to the application of magnetic resonance in medical imaging. They share the 2003 Nobel Prize in Physiology or Medicine.

The term "nuclear magnetic resonance" (NMR) was dropped because it was feared that people would associate it with atomic radiation. The technique was renamed "magnetic resonance imaging."

Multi-slice computed tomography (MSCT) and magnetic resonance imaging (MRI), when used with 3-D imaging technology, create vivid images of the interior of the human body. Dr. Richard Dirnhoter and Dr. Michael Thali and thier team of specialists at the University of Bern's Institute of Forensic Medicine, Switzerland are using these new imaging technologies to develop "Virtopsy"—a bloodless and minimally invasive "virtual autopsy" procedure to examine bodies for causes of death.

Virtopsy detects internal bleeding, bullet paths, and hidden fractures hard to find in a traditional autopsy. The MSCT and MRI aid in picturing fracture patterns, bone and missile fragmentation, brain contusion, 3-D bullet localization, gas embolism, and blood aspiration to the lung.

Unlike traditional autopsy, Virtopsy does not destroy human tissue. It can be used when religious beliefs prohibit, or families object to, the cutting open of the body. The developers of Virtopsy do not envision the procedure as a replacement for traditional autopsy but as a tool to be used in cases where dissection of the body is not feasible or where forensic evidence is particularly hard to visualize.

At the 1901 Pan-American Exposition in Buffalo, New York, an assassin shot President William McKinley twice at close range with a .32 caliber revolver. One bullet grazed McKinley's sternum (breastbone) and another penetrated his stomach.

A hastily assembled medical team, headed by a gynecological surgeon, operated immediately at the small Exposition hospital, but the second bullet could not be found. After cleaning the stomach cavity, the surgeon closed the incision with black silk thread and a straight sewing needle. A worried McKinley aide sent word to inventor Thomas Edison to rush an X-ray machine to Buffalo to find the stray bullet. It arrived but wasn't used.

The medical team reported that the president was improving. McKinley's family, Congress, and the public believed he was going to recover. Instead, he died the morning of September 14. At the autopsy, physicians found that the unrecovered bullet did not cause the death of the President through loss of blood and resultant shock. Instead, gangrene had developed along the path of the bullet, and McKinley died of septic shock due to bacterial infection.

Courtesy Stephen Ferry

In the "Dirty War" that took place between 1976 and 1983, Argentina's military regime committed massive human rights violations. Nearly 20,000 men, women and children were "disappeared" (los desaparecidos)—abducted, tortured, raped, and murdered—with no information provided on their whereabouts.

When the junta fell, the new civilian government invited forensic scientists from the American Association for the Advancement of Science to help investigate. Outside aid was critical—many Argentinean forensic professionals were implicated in the crimes of the junta, compromised by their association with the state, or poorly trained under a regime that discouraged investigation.

In 1984, anthropologist Clyde Snow recruited a group of Argentinean university students who lacked training in forensics, but were eager to learn. Together, they excavated hundreds of clandestine mass graves. This painstaking work led to the formation of the Equipo Argentino de Antropología Forense (Argentine Forensic Anthropology Team, or EAAF in the Spanish acronym), a nongovernmental organization dedicated to using forensic science to investigate human rights abuses.

"I'm not an advocate, I'm an expert. Unless you maintain…objectivity, you lose credibility.…and the best way is to let the bones speak for themselves."

—Clyde Snow, American forensic anthropologist

Bones as witnesses

In a landmark trial in 1985, forensic testimony helped convict six of nine former Argentinean military junta leaders for the deaths of the "disappeared." The forensic investigation focused on the exhumation of human remains at individual graves, using archaeological techniques and laboratory identification methods. The forensic volunteers, led by Clyde Snow, decided to present representative cases at the trial. One of the most dramatic was the case of Liliana Pereyra, a young woman who was abducted, tortured, raped, and murdered—after giving birth to a child whose identity and whereabouts are still unknown.

"Bones make great witnesses, they speak softly but they never forget and they never lie…."

—Clyde Snow, American forensic anthropologist

In 1984, after the fall of the Argentinean junta, anthropologist Clyde Snow recruited a group of Argentinean university students who lacked training in forensics, but were eager to learn. Together, they excavated hundreds of clandestine mass graves. This painstaking work led to the formation of the Argentine Forensic Anthropology Team (EAAF in the Spanish acronym), a nongovernmental organization dedicated to using forensic science to investigate human rights abuses.

In 1984, after the fall of the Argentinean junta, anthropologist Clyde Snow recruited a group of Argentinean university students who lacked training in forensics, but were eager to learn. Together, they excavated hundreds of clandestine mass graves. This painstaking work led to the formation of the Argentine Forensic Anthropology Team (EAAF in the Spanish acronym), a nongovernmental organization dedicated to using forensic science to investigate human rights abuses.

In 1984, after the fall of the Argentinean junta, anthropologist Clyde Snow recruited a group of Argentinean university students who lacked training in forensics, but were eager to learn. Together, they excavated hundreds of clandestine mass graves. This painstaking work led to the formation of the Argentine Forensic Anthropology Team (EAAF in the Spanish acronym), a nongovernmental organization dedicated to using forensic science to investigate human rights abuses.

In 1984, after the fall of the Argentinean junta, anthropologist Clyde Snow recruited a group of Argentinean university students who lacked training in forensics, but were eager to learn. Together, they excavated hundreds of clandestine mass graves. This painstaking work led to the formation of the Argentine Forensic Anthropology Team (EAAF in the Spanish acronym), a nongovernmental organization dedicated to using forensic science to investigate human rights abuses.

In 1984, after the fall of the Argentinean junta, anthropologist Clyde Snow recruited a group of Argentinean university students who lacked training in forensics, but were eager to learn. Together, they excavated hundreds of clandestine mass graves. This painstaking work led to the formation of the Argentine Forensic Anthropology Team (EAAF in the Spanish acronym), a nongovernmental organization dedicated to using forensic science to investigate human rights abuses.

In 1984, after the fall of the Argentinean junta, anthropologist Clyde Snow recruited a group of Argentinean university students who lacked training in forensics, but were eager to learn. Together, they excavated hundreds of clandestine mass graves. This painstaking work led to the formation of the Argentine Forensic Anthropology Team (EAAF in the Spanish acronym), a nongovernmental organization dedicated to using forensic science to investigate human rights abuses.

In 1984, after the fall of the Argentinean junta, anthropologist Clyde Snow recruited a group of Argentinean university students who lacked training in forensics, but were eager to learn. Together, they excavated hundreds of clandestine mass graves. This painstaking work led to the formation of the Argentine Forensic Anthropology Team (EAAF in the Spanish acronym), a nongovernmental organization dedicated to using forensic science to investigate human rights abuses.