Recessiv

Term from genetics. Recessive means "receding". Hereditary factors in "mixed" (heterozygous) alleles are recessive if they do not appear in the expression of the trait compared to a dominant hereditary factor. In order for the recessive factor to prevail, it must be "homozygous", i.e. it must be inherited from both parents. The hereditary factor must therefore be present twice.

A good example of "dominant and recessive" can be found in blood groups. The blood group is determined by the antigens on the surface of the erythrocytes. These are coded by different alleles. Dominant alleles code for the two most common blood groups A and B. If a person has alleles A and B at the same time, they produce both antigens at the same time and in the same quantity (codominance). Therefore, a person with the AG genotype also has the AB phenotype (and the AB blood group).

In blood group 0, there are no antigens on the cell surface of the red blood cells. The allele for O is recessive, and therefore there are two inheritance patterns for the blood groups in the ABO system:

Codominance for A and B

Dominant-recessive: A or B paired with the O allele.