CHAPTER 4 P ABO BLOOD GROUPS

ABO Blood groups are a case of Multiple Alleles ABO blood groups are a case of multiple alleles where there are three alternative alleles for one gene Discovered by Karl Landersteiner in the early 1900’s Controlled by a gene located on c-some 9. One combination of alleles in the ABO system exhibits codominance.

How is the ABO blood complex determined? ABO phenotype is ascertained by mixing a blood sample with antiserum containing type A or B antibodies Antigen – molecule ( often a surface protein), that is capable of elliciting the formation of antibodies Antibody – Protein (Immunoglobulin) produced in response to an antigenic stimulus  binds to antigen If the antigen is present on the surface of the person’s red blood cells, it will react with the antibody causing clumping or agglutination of the red blood cells

Phenotypes The 4 possible Phenotypes are  A antigen ( A Phenotype)  B antigen ( B Phenotype)  AB (A and B antigens present  AB Phenotype)  O (no antigens  O Phenotype)

Isoagglutinogen The ‘I’ designation is utilized for isoagglutinogen, another term for antigen I A – A blood  B antibody I B – B Blood  A Antibody I AB - AB Blood  No Antibodies  Universal Recipient (i)I O – O Blood  A and B Antibodies present  Universal Donor

I A and I B behave dominantly to I O but behave codominantly to each other

Rh Antigens Rh antigens were also thought to illustrate multiple allelism Important because of their involvement in the disorder Erythroblastosis fetalis  Form of Anemia  Occurs when mother is Rh- and father is Rh+ and those factors contribute to the allele of the fetus  This combination results in an immunological incompatibility of the mother and the fetus

If the fetal blood passes through a ruptured placenta at birth and enters the maternal circulation, the mother’s immune system will recognize the Rh antigen from the fetal blood and build immunities against it. During a second pregnancy, the antibody concentration becomes high enough that when they pass across the placenta into fetal circulation they will begin to destroy the fetal blood cells – fatal to fetus

Preventative Measures Rh – mothers are given anti-sera Destroys Rh-positive cells that may have entered the mother’s circulatory system

Rh Factors and blood typing reference

Fisher-Race Theory of Rh Inheritance Rh inheritance is controlled by 3 closely linked loci on each chromosome of a homologous pair Each locus has its own set of alleles which are Dd, Cc, and Ee. The D gene is dominant to the d gene, but Cc and Ee are co-dominant. The 3 loci are so closely linked that crossing over does NOT occur, and the 3 genes on one chromosome are always inherited together

Wiener Theory of Rh Inheritance There is one Rh locus at which occurs one Rh gene, but this gene has multiple alleles. For example, one gene R1 produces one agglutinogen (antigen) Rh1 which is composed of three "factors": rh', Rh(o), and hr''. The three factors are analogous to C, D, and e respectively The main difference between the Fisher-Race and Wiener theories is that the Fisher-Race theory has three closely linked loci, the Wiener theory has only one gene locus at which multiple alleles occur.

WEINER & FISHER-RACE TERMINOLOGY