ABO Blood Group; Rhesus Factor (Rh)/ Incompatibility Inheritance…2 ABO Blood Group; Rhesus Factor (Rh)/ Incompatibility

The ABO blood group system The ABO blood group exhibits the following: recessive alleles dominant alleles (IA and IB) co-dominance (IA and IB) multiple alleles (A, B and O) Red blood cells (erythrocytes) have surface markers, called antigens, which come in three or more varieties A, B, and O Possible genotypes: AA, AB, AO, BB, BO, and OO

Possible genotypes: AA, AB, AO, BB, BO, and OO Blood group A: IAIA or IAi (IAIO) Blood group B: IBIB or IBi (IBIO) Blood group AB: IAIB Blood group O: ii or IOIO

Both the A and B alleles are dominant over O, and co-dominant toward each other This means Individuals with the genotypes AA and AO both display phenotype A AB individuals display phenotype AB BB and BO individuals display phenotype B OO individuals display phenotype O

Antibodies to Antigens…1 Individuals without a specific allele see that allele’s antigen as foreign and produce antibodies which are reactive against that allele Individuals without B allele see the B-antigen as foreign and produce anti-B antibodies Individuals who do not have an A allele have antibodies which are reactive to A-antigen The existence of these antibodies makes it inadvisable to receive blood (via transfusions) from individuals whose red blood cells display the wrong (A or B) maker

ABO Donor/Recipient permutations

Inheriting the ABO blood group

Multiple Alleles…1 Multiple allelism is the phenomenon in which a gene has three or more alleles multiple allelic series Characteristics Multiple alleles of a series always occupy the same locus on a chromosome No crossing over occurs with multiple alleles of the same series because they occupy the same locus Multiple alleles always influence the same trait

Multiple Alleles…2 The wild type allele is almost always dominant The other alleles in the series (mutant types) may show dominance or there may be an intermediate phenotypic effect When any of two mutant multiple alleles are crossed, the phenotype is mutant type and not the wild type Remember Multiple alleles is the phenomenon in which the same gene has more than two alternative forms In normal Mendelian inheritance the gene has only two alleles These alleles combine in pairs to form the genotypes

The Rhesus blood group The Rhesus (Rh) blood group system (including the Rh factor) is one of the currently 30 human blood group systems The most important blood group system after ABO The Rh blood group system currently consists of 50 defined blood-group antigens among which the 5 antigens D, C, c, E, and e are the most important ones The commonly used terms Rh factor, Rh positive (Rh+) and Rh negative (Rh-) refer to the D antigen only

Rh factor The genetic information for the Rh factor is also inherited from our parents Inheritance is similar to, but independent of the ABO blood type alleles Two different alleles for the Rh factor Rh+ and Rh- An Rh positive Rh+ individual has at least one Rh+ allele Genotype could be either Rh+/Rh+ or Rh+/Rh An Rh negative Rh- person has a genotype of Rh- /Rh-

Rh factor genotype

Inheritance of the Rh factor Similar to the ABO grouping, the Rh system is based on antigens found on the surface of erythrocytes Each biological parent donates one of their two Rh alleles to their child An Rh- female can only pass an Rh- allele to her son or daughter An Rh+ male could pass either an Rh+ or Rh- allele to his son or daughter This couple could have: Rh+ children (Rh- from mother and Rh+ from father) or Rh- children (Rh- from mother and Rh- from father)

Possible genotype of offspring

Rh Incompatibility…1 If an Rh- person receives Rh+ blood, the body starts to make anti-Rh antibodies which remain in the blood Giving a second transfusion of Rh+ blood causes the previously formed anti-Rh antibodies to react against the donated blood, causing a severe reaction Under normal circumstances, human plasma does not contain anti-Rh antibodies Rh incompatibility is a problem is pregnant women carrying a foetus with a different Rh factor from the woman Under normal circumstances, human plasma does not contain anti-Rh antibodies. However, if an Rh- person receives Rh+ blood, the body starts to make anti-Rh antibodies which remain in the blood. If a second transfusion of Rh+ blood is later given, the previously formed anti-Rh antibodies will react against the donated blood, and may cause severe reaction.

Rh Incompatibility…2 If the foetus is Rh-, no problem will occur Example: Rh- woman/Rh+ foetus If the foetus is Rh-, no problem will occur Rh- blood does not contain the Rh antigen If on the other hand, the foetus is Rh+, an antigen- antibody response called haemolysis may occur in the foetal blood stream Haemolysis caused by Rh foetal-maternal incompatibility is called erythroblastosis foetalis (haemolytic disease of newborn)

Rh Incompatibility…3 Possible treatments A new born who has erythroblastosis can have all the blood slowly removed and replaced with antibody-free blood A blood transfusion into the unborn child can be performed if erythroblastosis is suspected Prevention Erythroblastosis can be prevented with an injection of an anti-Rh gamma2-globulin antibody preparation administered to Rh- mothers right after delivery These antibodies tie up foetal agglutinogens by producing antibodies In subsequent pregnancy the foetus is protected In the case of an Rh+ mother and an Rh- child, there are no complications, since the foetus cannot make antibodies Rh+ represents the marker-present phenotype while Rh- is the marker-absent one. The marker are the antigens of specific blood types.

Recap : Define the following terms in your own words Chromosome Gene Allele Diploid Gametes Features Homozygous Heterozygous Genetic engineering Dominant Recessive Monohybrid Meiosis Mitosis Sexual reproduction Asexual reproduction

chromosome The instructions that tell cells what an individual should look like are carried in these. There are 23 pairs of them in a normal human cell.

Genes These are the units which make up chromosomes. Responsible for inheritance of specific characteristics Alternative forms of the same gene are called alleles

diploid We use this word to describe cells which have the full complement of genetic material. In humans this is 46 chromosomes (23 pairs)

gametes Sperm and egg cells are both gametes. They each contain half the amount of DNA of normal diploid cells

Questions for discussion In what way can genetic counselling help an Rh+ woman carrying an Rh- foetus? References: The Biology Project website at the University of Arizona at http://www.biology.arizona.edu/human_bio/problem_sets/bloo d_types/rh_factor.html Genetics Home Reference at http://ghr.nlm.nih.gov/ The National Genome Research Institute at http://www.genome.gov/12511466 Verma, P.S. & Agarwal, V.K. (2003). Cell Biology, Genetics, Molecular Biology, Evolution and Ecology. S. Chand & Co. New Delhi: India