Q: My blood group is B positive and my husband's blood group is A positive and my son's is O negative, is this possible? If so, please explain genetically?

A:ABO Group A and B (& H) are antigens (proteins) found on the surface of red blood cells (and some other tissues). The ability to form these antigens is governed by genes inherited from parents. The pattern of genes we have is called genotype and the form in which they are expressed is called phenotype. It is the genotype (genetic make-up) which decides what the blood group (phenotype) will be. There are four possible blood groups in the ABO system: AB, A, B and O. Blood group A individuals possess A antigen on their red cells and have naturally occurring antibodies (anti-B) in their serum that react with group B and AB people. Blood group B individuals possess B antigen on their red cells and have naturally occurring antibodies (anti-A) in the serum that react with group A and AB people. Individuals with group AB possess both A and B antigens on their red cells and produce no naturally occurring antibodies. Finally, individuals with group O have neither A or B antigens on their red cells and have naturally occurring antibodies (anti- A and anti - B) in their serum that react with red cells from group A, B and AB people. In the ABO system there are three alleles (one member of a pair or series of genes that occupy a specific position on a specific chromosome): Ia - producing the antigen A, Ib - producing the antigen B and Io - producing neither antigen. IA and IB are co-dominant i.e. if both alleles are present, both antigens (A and B) will be formed on the surfaces of red blood cells and the individual will have blood group AB. Io is recessive and produces neither antigen and thus an individual will have blood group O if two of these alleles are present. The genotypic make-up can have 6 possibilities resulting in the following phenotypes: Ia Ib - AB, Ia Ia - A, Ia Io - A, Ib Ib - B, Ib Io - B, Io Io – O If either parent has group AB it will not be possible for any of the children to inherit Group O. If both parents have group O, all their children must have Group O and if both parents belong to blood group A (or B), it is still possible for some of their children to have Group O. Rh Group The Rh (rhesus) factor is a protein (antigen) present on the surface of red blood cells (RBCs). As it was first discovered in the rhesus monkey, it has been so named. Individuals carrying this antigen are called Rh-positive (Rh+) while those lacking it are Rh-negative blood group type (Rh-). Two closely linked but separate genes on the short arm of chromosome 1 encode Rh proteins - the RHD gene that encodes the D antigen and the RHCE gene encoding the Cc and Ee antigens. Rh-negative phenotype represents absence of D protein on RBCs and results from deletion of the RHD gene on both chromosomes. Rh antigens exist in 3 loci: Cc, Dd, and Ee. Of individuals who are Rh positive, 45% are homozygous and 55% are heterozygous. Frequency of Rh negativity is rare in Asians. The paternal heterozygosity determines the likelihood of an Rh-positive child being born to an Rh-negative mother. The Rh system is much more complicated than the ABO system because there are more than 30 combinations possible when inherited, however for general usage, the Rh proteins are grouped into two families - either positive or negative.