-
"Experiments on Plant Hybridization" is published.
Through experimentation, Gregor Mendel discovered that one inheritable trait would invariably be dominant to its recessive alternative. This model, later known as Mendelian inheritance or Mendelian genetics, provided an alternative to blending inheritance, which was the prevailing theory at the time. Mendel's work received little attention from the scientific community and was largely forgotten. -
DNA is identified as an acidic substance found in cell nuclei.
Friedrich Miescher devised different salt solutions eventually producing one with sodium sulfate. The cells were filtered. Since centrifuges were not present at this time the cells were allowed to settle at the bottom of a beaker. He then tried to isolate the nuclei free of cytoplasm. He subjected the purified nuclei to an alkaline extraction followed by acidification resulting in a precipitate being formed which Miescher called nuclein (now known as DNA). -
The chromosome theory of heredity is proposed.
Sutton was the first to point out that chromosomes obey Mendel's rules—the first clear argument for the chromosome theory of heredity. Sutton worked with grasshopper chromosomes, and it was in this paper that he showed that chromosomes occur in distinct pairs, which segregate at meiosis. -
The word "genetics" is coined.
Bateson was the first to suggest the word "genetics" (from the Greek gennō, to give birth) to describe the study of inheritance and the science of variation in a personal letter to Alan Sedgwick. Bateson first used the term "genetics" publicly at the Third International Conference on Plant Hybridization in London in 1906. -
First ever linkage map created.
Columbia undergraduate Alfred Sturtevant (working with T.H. Morgan) provides his analysis of genetic “linkage groups,” which became classical method of chromosome mapping that we still use today. In 1913, he determined that genes were arranged on chromosomes in a linear fashion, like beads on a necklace. He also showed that the gene for any specific trait was in a fixed location (locus). -
Genetic material can be transferred laterally between bacterial cells.
In 1946 and 1947, Joshua Lederberg took a leave of absence to study under the mentorship of Edward Tatum at Yale. They showed that the bacterium Escherichia coli entered a sexual phase during which it could share genetic information through bacteriaunder the mentorship of Tatum at Yale University. Lederberg and Tatum showed that the bacterium Escherichia coli entered a sexual phase during which it could share genetic information through bacterial conjugation. -
In DNA, there are equal amounts of A and T, and equal amounts of C and G.
In DNA, there are equal amounts of A and T, and equal amounts of C and G, as shown by Erwin Chargaff. However, the A+T to C+G ratio can differ between organisms. -
DNA is the molecule that mediates heredity.
Alfred Hershey and Martha Chase show through bacteriophage labeling experiments that DNA is the genetic material. 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. -
DNA is defined by a double-helix structure.
James D. Watson and Francis Crick were the two co-discoverers of the structure of DNA in 1953. They used x-ray diffraction data collected by Rosalind Franklin and proposed the double helix or spiral staircase structure of the DNA molecule. Their article, Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid, is celebrated for its treatment of the B form of DNA (B-DNA), and as the source of Watson-Crick base pairing of nucleotides. -
The genetic code is cracked.
A number of researchers (including Nirenberg, Matthaei, Leder, and Khorana) used RNA homopolymer and heteropolymer experiments as well as tRNA labeling experiments to crack the genetic code. -
The first restriction enzyme is purified.
Hamilton Smith discovered the first type II restriction enzyme that is now reffered to as Hindll. -
DNA sequencing technology is developed.
Fred Sanger and colleagues introduced the "dideoxy" chain-termination method for sequencing DNA molecules, also known as the "Sanger method". It was a major breakthrough and allowed long stretches of DNA to be rapidly and accurately sequenced. The new method was used by Sanger and colleagues to sequence human mitochondrial DNA. -
DNA microarrays are invented.
Pat Brown and colleagues discover a DNA microarray (also commonly known as gene chip, DNA chip, or biochip) is a collection of microscopic DNA spots attached to a solid surface. -
The sequence of the human genome is released.
Key findings include
1. There are approximately 23,000 genes in human beings, the same range as in mice and roundworms. Understanding how these genes express themselves will provide clues to how diseases are caused.
2. Between 1.1% to 90% of the genes code for proteins
3. The human genome has significantly more segmental duplications than other mammalian genomes.
4. At the time when the draft sequence was published less than 7% of protein families appeared to be vertebrate specific. -
The first cloning of a mammal is performed.
Ian Wilmut and colleagues, from the Roslin institute in Scotland, clone the first anaimal, Dolly the sheep.After cloning was successfully demonstrated through the production of Dolly, many other large mammals have been cloned, including horses and bulls.
