GenotypeAnti-M
Reaction		Anti-N
Reaction		Blood
Type
 
MM+-M
NN-+N
MN++MN
The human MN blood group is determined by codominant alleles for two specific molecules located on the surface of red blood cells.

Homozygous MM individuals have red blood cells with only M molecules.

Homozygous NN individuals have red blood cells with only N molecules.

Heterozygous (MN) individuals have both M and N molecules.