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A:

See adenine

AA:

See amino acid

AD:

See autosomal dominant

Allele:

An alternate form of a gene at a given locus or location in the genome. Each locus has two alleles, one inherited from each parent.

Affected:

An individual diagnosed with a disease or disorder of who shows signs or symptoms of a condition.

Allelic heterogeneity:

Variant alleles found at a single locus which can result in the same phenotype.

Amino Acid:

One of 20 molecules made by instructions contained in DNA. These molecules are linked together to form proteins.

Anticipation:

An earlier age of onset and/or greater severity of disease with subsequent generations in a family seen with certain genetic disorders, notably the trinucleotide repeat disorders.

AR:

See autosomal recessive

Association:

A statistical relationship between two variables. Most commonly an allele found more or less frequently with a specific disease than in the general population.

Autonomy:

The right to make decisions about oneself.

Autosome:

A chromosome that is not a sex chromosome. Humans have 22 pairs of autosomes.

Autosomal:

Inheritance of a gene on an autosome. A disease caused by a gene not on a sex chromosome has autosomal inheritance.

Autosomal Dominant:

A disease caused by a gene not on a sex chromosome. The phenotype/disease/trait is expressed by individuals who have one copy of the gene variant. Individuals with an autosomal dominant condition have a 50% chance of passing the gene variant to offspring with each pregnancy.

Autosomal Recessive:

A disease caused by a gene not on a sex chromosome. The phenotype/disease/trait is expressed by individuals who have inherited two genetic variants at the same locus or gene. Most often one changed copy of the gene is inherited from each parent.