Restriction endonucleases are enzymes that make double-
DNA fragments can be separated with the use of gel electrophoresis and visualized by staining the gel with a dye that is specific for nucleic acids or by labeling the fragments with a radioactive or chemical tag.
In gene cloning, a gene or a DNA fragment is inserted into a bacterial cell, where it will multiply as the cell divides.
Plasmids, small circular pieces of DNA, are often used as vectors to ensure that a cloned gene is stable and replicated within the recipient cells. Expression vectors contain sequences necessary for foreign DNA to be transcribed and translated.
The polymerase chain reaction is a method for amplifying DNA without cloning.
Genes can be isolated by creating a DNA library: a set of bacterial colonies or viral plaques that each contain a different cloned fragment of DNA. A genomic library contains the entire genome of an organism; a cDNA library is created from mRNA that is converted into cDNA.
Positional cloning uses linkage relations to determine the location of genes without any knowledge of their products.
The Sanger (dideoxy) method of DNA sequencing uses special substrates for DNA synthesis (dideoxyribonucleoside triphosphates) that terminate synthesis after they have been incorporated into the newly made DNA. Next-
Short tandem repeats, or microsatellites, are used to identify people by their DNA sequences (DNA fingerprinting).
Forward genetics begins with a phenotype and conducts analyses to locate the responsible genes. Reverse genetics starts with a DNA sequence and conducts analyses to determine its phenotypic effect.
Transgenic animals, produced by injecting DNA into fertilized eggs, contain foreign DNA that is integrated into a chromosome. Knockout mice are transgenic mice in which a normal gene is disabled. Knock-
The mouse (Mus musculus) is an excellent model genetic organism because of its similarity to humans, small size, and short generation time.
RNA interference is used to silence the expression of specific genes.
Techniques of molecular genetics are being used to create products of commercial importance, to develop diagnostic tests, and to treat diseases.