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Glossary Molecular Biology and Computational Biology

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Additive genetic effectsWhen the combined effects of alleles at different loci are equal to the sum of their individual effects. (ORNL)

Adenine (A) A nitrogenous base, one member of the base pair AT (adenine-thymine).
Algorithm< A fixed procedure embodied in a computer program. (NCBI)

Alignment The process of lining up two or more sequences to achieve maximal levels of identity (and conservation, in the case of amino acid sequences) for the purpose of assessing the degree of similarity and the possibility of homology. (NCBI)

Alignment Representation of a prediction of the amino acids in tertiary structures of homologues that overlay in three dimensions. Alignments held by SMART are mostly based on published observations (see domain annotations for details), but are updated and edited manually. (SMART)

All-alpha A class that has the number of secondary structures in the domain or common core described as 3-, 4-, 5-, 6- or multi- helical. (SCOP)

All-beta A class that includes two major fold groups: sandwiches and barrels. The sandwich folds are made of two beta-sheets which are usually twisted and pack so their strands are aligned. The barrel fold are made of single beta-sheet that twists and coils upon itself so, in most cases, the first strand in the beta sheet hydrogen bond to the last strand. The strand directions in the two opposite sides of a barrel fold are roughly orthogonal. Orthogonal packing of sheets is also seen in a few special cases of sandwich folds (SCOP)

Allele Alternative form of a genetic locus; a single allele for each locus is inherited from each parent (e.g., at a locus for eye color the allele might result in blue or brown eyes). (ORNL)

Allele One of the variant forms of a gene at a particular locus, or location, on a chromosome. Different alleles produce variation in inherited characteristics such as hair color or blood type. In an individual, one form of the allele (the dominant one) may be expressed more than another form (the recessive one). (NHGRI)

Allogeneic Variation in alleles among members of the same species. (ORNL)

Alternative splicing Different ways of combining a gene's exons to make variants of the complete protein (ORNL)

Amino acid Any of a class of 20 molecules that are combined to form proteins in living things. The sequence of amino acids in a protein and hence protein function are determined by the genetic code. (ORNL)

Amplification An increase in the number of copies of a specific DNA fragment; can be in vivo or in vitro.
Adding pertinent information such as gene coded for, amino acid sequence, or other commentary to the database entry of raw sequence of DNA bases.

Anticipation Each generation of offspring has increased severity of a genetic disorder; e.g., a grandchild may have earlier onset and more severe symptoms than the parent, who had earlier onset than the grandparent.

Antisense Nucleic acid that has a sequence exactly opposite to an mRNA molecule made by the body; binds to the mRNA molecule to prevent a protein from being made.

Apoptosis Programmed cell death, the body's normal method of disposing of damaged, unwanted, or unneeded cells.

Array (of hairpins) An assemble of alpha-helices that can not be described as a bundle or a folded leaf. (SCOP)

Arrayed library Individual primary recombinant clones (hosted in phage, cosmid, YAC, or other vector) that are placed in two-dimensional arrays in microtiter dishes. Each primary clone can be identified by the identity of the plate and the clone location (row and column) on that plate. Arrayed libraries of clones can be used for many applications, including screening for a specific gene or genomic region of interest.

Assembly Putting sequenced fragments of DNA into their correct chromosomal positions. (ORNL)

Autoradiography A technique that uses X-ray film to visualize radioactively labeled molecules or fragments of molecules; used in analyzing length and number of DNA fragments after they are separated by gel electrophoresis. (ORNL)

Autosomal dominant A gene on one of the non-sex chromosomes that is always expressed, even if only one copy is present. The chance of passing the gene to offspring is 50% for each pregnancy.

Autosome A chromosome not involved in sex determination. The diploid human genome consists of a total of 46 chromosomes: 22 pairs of autosomes, and 1 pair of sex chromosomes (the X and Y chromosomes).

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