Genomics is the study of the structure, function, and inheritance of the genome (entire set of genetic material) of an organism. A major part of genomics is determining the sequence of molecules that make up the genomic DNA content of an organism. Every organism contains a basic set of chromosomes, unique in number and size for every species, that includes the complete set of genes plus any DNA between them. While the term genome was not brought into use until 1920, the existence of genomes has been known since the late 19th century, when chromosomes were first observed as stained bodies visible under the microscope. The initial discovery of chromosomes was then followed in the 20th century by the mapping of genes on chromosomes based on the frequency of exchange of parts of chromosomes by a process called chromosomal crossing over, an event that occurs as a part of the normal process of recombination and the production of sex cells (gametes) during meiosis. The genes that could be mapped by chromosomal crossing over were mainly those for which mutant phenotypes (visible manifestations of an organism’s genetic composition)had been observed, only a small proportion of the total genes in the genome. The discipline of genomics arose when the technology became available to deduce the complete nucleotide sequence of genomes, sequences generally in the range of billions of nucleotide pairs.
Functional Genomics:
Analysis of genes at the functional level is one of the main uses of genomics, an area known generally as functional genomics. Determining the function of individual genescan be done in several ways. Classical, or forward, genetic methodology starts with a randomly obtained mutant ofinteresting phenotype and uses this to find the normal gene sequence and its function. Reverse genetics starts with the normal gene sequence (as obtained by genomics), induces a targeted mutation into the gene, then, by observing howthe mutation changes phenotype, deduces the normal function of the gene. The two approaches, forward and reverse, are complementary. Often a gene identified by forward genetics has been mapped to one specific chromosomal region, and the full genomic sequence reveals a gene in this position with an already annotated function.
Functional Genomics:
Analysis of genes at the functional level is one of the main uses of genomics, an area known generally as functional genomics. Determining the function of individual genescan be done in several ways. Classical, or forward, genetic methodology starts with a randomly obtained mutant ofinteresting phenotype and uses this to find the normal gene sequence and its function. Reverse genetics starts with the normal gene sequence (as obtained by genomics), induces a targeted mutation into the gene, then, by observing howthe mutation changes phenotype, deduces the normal function of the gene. The two approaches, forward and reverse, are complementary. Often a gene identified by forward genetics has been mapped to one specific chromosomal region, and the full genomic sequence reveals a gene in this position with an already annotated function.
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