The ability of heterozygous lymphoid cells to produce only one allelic form of antigen-specific receptor when they have the genetic endowment to produce both. Genes other than those for the specific receptors are usually expressed codominantly.
This occurs when the use of a gene from the maternal or paternal chromosome prevents the use of the other. This is seen with antibody and T-cell receptor genes.
Humans and many other organisms are diploid, i.e. they have two copies of each chromosome (one inherited from each parent) in all their somatic cells. Both chromosomes within the pair contain essentially the same genes, but these genes may contain a small number of nucleotide differences. The two copies of a gene on a pair of chromosomes are called alleles.