Allele: A variation of a gene.
Antigen: A substance or molecule capable of activating or stimulating an immune response. Immunogen is an interchangeable term.
Cluster of differentiation (CD): Cell surface membrane receptors or markers used to characterize cells by their functions. Used in flow cytometry to identify cells, can also be used to identify cell clones associated with leukemias and lymphomas.
Codominant: Mendelian law that two genes are inherited and expressed together. One does not dominate the other.
Epitope: A region on an antigen that is the site of antigenic stimulation for the immune response. Antibodies bind to this part of the antigen.
Exon: The portion of a gene that codes for amino acids. Also refers to the gene sequence that is expressed in the protein.
Gene: A segment of DNA that is transcribed and translated into a protein.
Gene locus: A region or cluster of genes that are closely related. These are usually within the same exon and give rise to similar gene products with slight variation. HLAs have four main HLA loci: A, B, C, and D. D can be further subdivided into DP, DQ, and DR.
Genotype: The complete set of genes inherited by both parents to a viable offspring.
Germinal center: Important sites of antibody affinity maturation.
Haplotype: A set of alleles that are inherited from one parent.
Heterozygous: Having two different kinds of genes. Example: XY sex chromosomes.
Homozygous: Having two of the same kinds of genes. Example: XX sex chromosomes.
Linkage disequilibrium: The phenomenon that occurs when the inheritance of certain gene patterns is higher than statistically anticipated in given populations.
Polymorphism: Several different forms or genetic variations of genes in a given population.
