A

Acquired genetic mutation

See: somatic cell genetic mutation

Additive genetic effects

When the combined effects of alleles at different loci are equal to the sum of their individual effects.
See also: anticipation, complex trait

Adenine (A)

A nitrogenous base, one member of the base pair AT (adenine-thymine).
See also: base pair, nucleotide

Affected relative pair

Individuals related by blood, each of whom is affected with the same trait. Examples are affected sibling, cousin, and avuncular pairs.
See also: avuncular relationship

Aggregation technique

A technique used in model organism studies in which embryos at the 8-cell stage of development are pushed together to yield a single embryo (used as an alternative to microinjection).
See also: model organisms

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).
See also: locus, gene expression

Allogeneic

Variation in alleles among members of the same species.

Alternative splicing

Different ways of combining a gene's exons to make variants of the complete protein

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.

Amplification

An increase in the number of copies of a specific DNA fragment; can be in vivo or in vitro.
See also: cloning, polymerase chain reaction

Animal model

See: model organisms

Annotation

Adding pertinent information such as gene coded for, amino acid sequence, or other commentary to the database entry of raw sequence of DNA bases.
See also: bioinformatics

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.
See also: additive genetic effects, complex trait

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.
See also: transcription

Apoptosis

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

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.
See also: library, genomic library, gene chip technology

Assembly

Putting sequenced fragments of DNA into their correct chromosomal positions.

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.

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.
See also: autosome, dominant, gene

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).
See also: sex chromosome

Avuncular relationship

The genetic relationship between nieces and nephews and their aunts and uncles.

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