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Molecular Biology and Bioinformatics Glossary




A statistical parameter used in calculating BLAST scores that can be thought of as a natural scale for scoring system. The value lambda is used in converting a raw score (S) to a bit score (S'). (NCBI)


An unordered collection of clones (i.e., cloned DNA from a particular organism) whose relationship to each other can be established by physical mapping.
See also: genomic library, arrayed library (ORNL)


The proximity of two or more markers (e.g., genes, RFLP markers) on a chromosome; the closer the markers, the lower the probability that they will be separated during DNA repair or replication processes (binary fission in prokaryotes, mitosis or meiosis in eukaryotes), and hence the greater the probability that they will be inherited together. (ORNL)

Linkage disequilibrium

Where alleles occur together more often than can be accounted for by chance. Indicates that the two alleles are physically close on the DNA strand.
See also: Mendelian inheritance (ORNL)

Linkage map

A map of the relative positions of genetic loci on a chromosome, determined on the basis of how often the loci are inherited together. Distance is measured in centimorgans (cM). (ORNL)

Local Alignment

The alignment of some portion of two nucleic acid or protein sequences (NCBI)


Numbers of domains that are thought from SwissProt annotations to be present in different cellular compartments (cytoplasm, extracellular space, nucleus, and membrane-associated) are shown in annotation pages. (SMART)


Determination of the original position (locus) of a gene or other marker on a chromosome. (ORNL)

Locus (pl. loci)

The position on a chromosome of a gene or other chromosome marker; also, the DNA at that position. The use of locus is sometimes restricted to mean expressed DNA regions.
See also: gene expression (ORNL)

Long-Range Restriction Mapping

Restriction enzymes are proteins that cut DNA at precise locations. Restriction maps depict the chromosomal positions of restriction-enzyme cutting sites. These are used as biochemical "signposts," or markers of specific areas along the chromosomes. The map will detail the positions where the DNA molecule is cut by particular restriction enzymes. (ORNL)

Low Complexity Region (LCR)

Regions of biased composition including homopolymeric runs, short-period repeats, and more subtle overrepresentation of one or a few residues. The SEG program is used to mask or filter LCRs in amino acid queries. The DUST program is used to mask or filter LCRs in nucleic acid queries. (NCBI)


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