rhesus blood group


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rhesus blood group

a form of human blood variation in which about 85% of the UK population possess an RH factor (DANTIGEN) on the surface of red blood cells. Such people are described as being Rh-positive; those without the factor are Rh-negative. Unlike the ABO BLOOD GROUP there is normally no rhesus ANTIBODY, unless a Rh-negative person is sensitized by a rhesus antigen, which may happen, for example, in a blood transfusion or when a Rh-negative mother receives blood cells from a Rh-positive foetus (see RHESUS HAEMOLYTIC ANAEMIA). The blood group factor is controlled by a single autosomal gene on chromosome number 1, with two principal alleles. The allele for the Rh-factor is dominant.