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1856-1863
Gregor Mendel discovers the basic laws of inheritance by experimenting with 7 characteristics of pea plants.
He proposes three laws:
-The law of dominance and recessiveness (3:1 dominant-to-recessive ratio)
-The law of random fertilization
-The law of segregation
* He publishes his findings in 1865 -
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Miescher studies the nuclei of white blood cells obtained from pus, and discovers a substance that contains nitrogen and phosphorus, which he names nuclein. In 1874 'nuclein' is renamed nucleic acid, when Miescher separates it into protein and acid components. Today it is kknown as DNA, or deoxyribonucleic acid.
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While studying cells he discovers a substance he names chromatin, along with its relation with chromosomes.
By using fins and gills of salamanders he studies the process of (body and prokaryote) cell division, which he calls mitosis. -
Through work with sea urchin eggs, Boveri dicovers that, contrary to what was previously believed, the nuclei of a sperm and an egg do not fuse, but, as they contain half set of chromosomes (haploid) contribute to the same amount of genetic information.
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Gregor Mendel's neglected laws are rediscovered (independently) by Carl Correns, Hugo de Vries and Erich von Tschermak.
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Carl Erich Correns discovers incomplete dominance. A case in some gene pairs where neither gene is dominant nor recessive (the genes work together producing a blended or mixed trait).
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Soon after Mendel's theory is rediscovered, Sutton studies grashopers' sperm cells. By understanding Mendel's work as well as meiosis, he proposes that chromosomes are located inside a nucleus, and inside chromosomes genes are located.
His theory along with Theodor Boveri's are now called the
Boveri-Sutton chromosome theory. -
Bateson proposes that the action of several genes together may result in one trait. Thus, different combinations of alleles result in a different shade of eye colour, for example.
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He presents the basic terminology of genetics:
-Genes:units of heredity
-Genotype: the genetic constitution of an organism
-Phenotype: an organism's totality of inherited characteristics that appear in an organism -
Morgan demonstrates the hypothesis that genes are located on chromosomes.
He publishes in one of his books three principles:
- Distinct pairs of genes located on chromosomes like beads on a string bear hereditary information, which combine during reproduction.
- Certain characteristics are sex-linked.
-Genes close to one another tend to remain together. But sometimes, as a mechanistic consequence of reproduction, this linkage between genes is broken, allowing new combinations of traits. -
While working in Thomas Morgan's laboratory, he creates the first genetic map of a chromosome.
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Brachet proves that DNA is found in chromosomes and that RNA is present in the cytoplasm of all cells.
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They study together Neurospora crassa, a bread mold, and propose the following hypothesis: "One gene specifies the production of one enzyme." It is said today, more accurately, that each gene specifies the production of a single polypeptide (a protein or protein component.) Thus, two or more genes may contribute to the synthesis of a particular enzyme. In addition, some products of genes are not enzymes but structural proteins.
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They studied together the bacterial genetics and , in their Fluctuation Test, propose that bacteria, genetic mutations arise in the absence of selection, rather than being a response to selection.
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Through their experiments, they are able to identify DNA as the "transforming principle" responsible for specific characteristics in bacteria.
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He discovers regularity in proportions of DNA bases for different species. In each organism he studies, the amount of adenine (A) approximately equals that of thymine (T), and guanine (G) equals cytosine (C).
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She was able, by using X-ray diffraction, to make images of DNA molecules, which suggested that it has a spiral shape.
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They discover the molecular structure of DNA and make a model of it.
Their discovery suggested that DNA—not a protein, as was widely imagined—was the master molecule that contains the genes, self-replicates and recombines during reproduction. -
He is able to crystallize DNA polymerase, the enzyme needed for synthesizing DNA.
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Theye report that humans have 46 chromosomes, instead of 48, as previously believed.
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Marshall Nirenberg discovers the first "triplet"—a sequence of three bases of DNA that codes for one of the twenty amino acids that serve as the building blocks of proteins. Within five years, the entire genetic code was deciphered.
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Mary Weiss and Howard Green employ somatic cell hybridization to advance human gene mapping.
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In 1969, Jonathan Beckwith detaches, or isolates, a bacterial gene.
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Howard Temin and David Baltimore independently discover reverse transcriptase, an enzyme that makes DNA from an RNA template.
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Paul Berg assembles the first DNA molecules that combine genes from different organisms.
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In his research involving Bacteriophage MS2, he was the first to establish the complete nucleotide sequence of a gene.
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They report the construction of functional organisms that combine and replicate genetic information from different species, thus showing that genetically engineered DNA molecules may be cloned in foreign cell.
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Fiers establishes the complete nucleotide sequence of a viral genome (bacteriophage MS2).
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Walter Gilbert and Frederick Sanger separately formulate techniques for sequencing DNA. The methods invented by them make it possible to read the nucleotide sequence for entire genes, which run from 1,000 to 30,000 bases long.
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David Botstein initiates the use of restriction fragment length polymorphisms (RFLPs) in mapping genes to indicate genetic differences among individuals.
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Kary Mullis conceives and helps develop polymerase chain reaction (PCR), which is used for rapid multiplication of DNA fragments.
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Hood develops develops the automated sequencer, which uses fluorescent tracers instead of radioisotopes to label the DNA.
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The effort for sequencing the human genome begins.
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In the United States, the government-funded Human Genome Project was launched in 1990.
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Venter portrays a new fast approach to gene discovery usicng Expressed Sequence Tags (ESTs), which offer an efficient way to find genes and explore their functions.
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The genome of Haemophilus influenzae Rd. is sequenced.
Success in its sequence (taking about a year) demonstrated that random shotgun sequencing could be applied to whole genomes with speed and accuracy. -
Scientists in Maryland sequence the genome of Methanococcus jannaschiiand, a type of archaea, and find many genes unseen until then.
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About 600 scientists around the world finish sequencing the genome of baker’s yeast, which carries versions of many human genes.
Results showed that yeast has about 6,000 genes. -
Dolly becomes the first mammal to be cloned from an adult somatic cell, using the process of nuclear transfer.
She had three mothers: one provided the egg, another the DNA and a third carried the cloned embryo to term. -
A microscopic worm called Caenorhabditis elegans has its genome sequenced.
Many genes in the worm are also present in humans.
It has primitive digestive and neuromuscular systems.
Its translucent body pemits easy observation of biological development as the worm grows from a fertilized egg to an adult containing 959 cells exactly. -
Drosophila's entire genome is sequenced and collected by Celera Genomics, in union with the federally funded Berkeley Drosophila Genome Project (BDGP), in the course of about eight months.
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The human genome is sequenced and collected by Celera Genomics.
Gathering of the 3.12 billion base pairs of DNA required some 500 million trillion sequence comparisons, -
It was found that humans have around 30,000 genes that carry within them the instructions for making the body's diverse collection of proteins.
It was also reported that the DNA of human beings is 99.9% alike. -
In April 2001, Celera Genomics announce the achievement
of a draft mouse genome sequence. It is found that more than 700 mouse genes are present in humans. -
Despite some opposition to the genome sequence of another rodent, in 2004 a draft of the rat genome appears.
Nature reports that rats have many of the genes known to cause disease in humans. -
Scientists have identified how a protein enables sections of 'junk' DNA to be cut and pasted within genetic code – a finding which could speed development of gene therapies.
