A

Allele

Alternative forms of one and the same gene. Every human being always has two alleles for one and the same gene on account of the diploid set of chromosomes.

Allergy

An overreaction by the immune system triggered by certain substances (allergens). In the case of a food allergy, certain food constituents are not tolerated by the body and are attacked by the body's immune system.

Amino Acid

Organic acids that are physiologically very important. They are the building blocks of proteins.

Antigen

A molecular structure which is identified by the immune system as being foreign and which triggers an immune response.