Sequencing: determining the sequence of genetic letters in a piece of DNA or an entire genome. (GNN)

A laboratory technique used to determine the exact sequence of ("nucleotide") bases (A, C, G, and T) in a ("nucleic acid") molecule. The order of “base sequences” in a DNA or RNA molecule or the order of “amino acids” in a “protein.” (HGPIA) The "DNA sequence" carries the information a "cell" needs to assemble protein and RNA molecules. DNA sequence information is important to scientists investigating the functions of genes. (NHGRI) Researchers have found that DNA variations outside the “exons” can affect gene activity and protein production and lead to "genetic disorders" - variations that “whole exome sequencing” would miss. "Whole genome shotgun sequencing" determines the order of all the nucleotides in an individual’s DNA and can determine variations in any part of the "genome." (GHR) Editor’s note - “sequencing” may refer to decoding a protein, a piece of DNA, a piece of RNA, or a full genome.

DNA Sequencing: the sequence of consecutive DNA letters spanning all the chromosomes of a cell from start to finish. (GNN) A multistage process that includes “cloning,” physical mapping, sub-cloning, determination of the DNA sequence, and information analysis. (MeSH) A method to determine the base sequence of DNA. The technology of DNA sequencing was made faster and less expensive as a part of the “Human Genome Project.” (NHGRI) The investigation of genetic sequences has been vital in our understanding of the genetic basis of human disease. (Brooker, 422) Also referred to as ‘DNA sequence analysis’ and ‘genome sequencing.'

Family Genome Sequencing: compares genome sequences to trace genetic disease origins. Compares the complete genome sequences of the members of a family. As the cost of genome sequencing falls, consulting the parents' genomes is helping to reveal the genes behind very rare diseases. (Lewis, 84-85)

Nanomaterial Sequencing: DNA molecule passes through 'nanopores' of a 'graphene' sheet conducting electricity differently depending on the (DNA) base passing through. (Lewis, 429)

Overlapping: an uncommon genetic arrangement where part of the... DNA sequence of one gene forms part or all of the sequence of another. (Lawrence) (During the Human Genome Project), researchers 'cut' several genomes worth of DNA into overlapping pieces of about 40,000 "DNA fragments," then randomly cut (those) pieces into small fragments. Computer "algorithms" eased the assembly of many short pieces of DNA, with overlapping end sequences, into longer sequences. (Lewis, 426)

Sanger Sequencing: widely used method of determining the order of bases in DNA. (HGPIA) Complementary copies of an unknown DNA sequence are cut into different-size pieces differing from each other by an end base. The result is a collection of partial sequences from which the end bases reveal the sequence. (Lewis, 430) The original sequencing technology. It was a breakthrough that helped scientists determine the human genetic code, but it is time-consuming and expensive. The Sanger method has been automated to make it faster and is still used in laboratories today to sequence short pieces of DNA, but it would take years to sequence all of a person’s genome. (GHR) 

Whole Exome Sequencing: with next-generation sequencing, it is now feasible to sequence large amounts of DNA, for instance all the pieces of an individual’s DNA that provide instructions for making proteins. These pieces, called exons, are thought to make up 1 percent of a person’s genome. Together, all the exons in a genome are known as the "exome," and the method of sequencing them is known as whole exome sequencing. This method allows variations in the protein-coding region of any gene to be identified, rather than a select few genes. Because most known "mutations" that cause disease occur in exons, whole exome sequencing is thought to be an efficient method to identify possible disease-causing mutations. (GHR)

Whole Genome Shotgun Sequencing: laboratory technique for determining the DNA sequence of an organism's genome. The method involves breaking the genome into a collection of small DNA fragments that are sequenced individually. A computer program looks for overlaps in the DNA sequences and uses them to place the individual fragments in their correct order to reconstitute the genome. (NHGRI) Can determine the DNA sequence for nearly the entire genome of an individual. (NCIt) One of two approaches used in Human Genome Project. (This process) shatters the entire genome, then rebuilds it. (Lewis, 426-428) The first step... is to copy a genome many times, then shred the copies into fragments of DNA that can be 'read' by machines. Next, computers identify the fragments that belong next to each other in the genome and assemble them into a complete genome sequence. (GNN) Relies on breaking genomes down into small pieces that can be easily read by DNA sequencing machines. (Venter, 68) A sequencing method that involves randomly sequenced cloned pieces of the genome, with no foreknowledge of where the piece originally came from. This can be contrasted with 'directed' strategies, in which pieces of DNA from known chromosomal locations are sequenced. Because there are advantages to both strategies, researchers used both shotgun and directed strategies in combination to sequence the human genome. (HGPIA) Also referred to 'shotgun sequencing.'

RNA Sequencing: a multistage process that includes cloning, physical mapping, sub-cloning, sequencing, and information analysis of an RNA sequence. (MeSH) Also referred to as ‘RNA sequence analysis.’

Sequencing Timeline: new technologies that allow rapid sequencing of large amounts of DNA were developed. (GHR) 

1965: Robert Holley published the sequence (77 ribonucleotides) of (alanine) "transfer RNA.” (Venter, 48) 

1967: Fred Sanger determined the sequence (120 nucleotides) of a small “ribosomal RNA.” (Venter, 48)

1976: the first actual genome that was successfully decoded was an RNA virus genome - the bacteriophage 'MSa' by Walter Fiers. (Venter, 48)

1977: Fred Sanger determined the first DNA virus genome - the bacteriophage 'phi X 174' in 1977. (Venter, 48-49)

1995: (the genome of the) first free living organism, H. influenzae, was sequenced (1.8 million base pairs). (GNN)

1996: some 600 scientists around the world finished sequencing the (16 chromosomes of the) genome of baker’s “yeast” - “S. cerevisiae.”  The organism that carries versions of many human genes. Yeast was the third species, after two types of bacteria, to have its genome (12.2 million base pairs) completely sequenced. (GNN)

1998: the nematode worm “C. elegans” genome was sequenced (100 million base pairs). (GNN, Genetics and Genomics Timeline)

1999: the (fruit fly) “Drosophila melanogaster” genome was sequenced (122 million base pairs). (GNN, Genetics and Genomics Timeline)

2003: The "Human Genome Project" sequenced the entire human genome (3.3 billion base pairs). (HGPIA)