A term used in genetics to loosely mean “half of a genotype.” A haplotype is a combination of genes inherited as a group from one parent. It can technically refer to all of the genes from that parent, or to just a specific group of genes from one chromosome, or even one area on a chromosome. There are also more complicated definitions involving more advanced genetic concepts such as single-nucleotide polymorphisms and short tandem repeats.

In blood banking circles, however, “haplotype” is usually used to refer to the closely linked alleles inherited from one parent for a particular blood group. For example, in the Rh blood group, the alleles for D and CcEe expression were previously thought to be passed from a parent to a child as a unit (see the discussion on Rh genetics for more detail). So, for Rh, a child receives one “Rh haplotype” from his mother and one from his father, and the combination of alleles determines the Rh antigens that will be expressed on his red blood cells. The same term is used for non-red cell antigenic groups such as the “Human Leukocyte Antigen” or “HLA” system.

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