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

2. 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

3. 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

4. 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

5. 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

6. ABO Donor/Recipient permutations

7. Inheriting the ABO blood group

9. 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

10. 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

11. 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

12. 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-

13. Rh factor genotype

14. 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)

15. Possible genotype of offspring

16. 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.

17. 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)

18. 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.

19. 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

20. 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.

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

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

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

24. 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 d_types/rh_factor.html
Genetics Home Reference at
The National Genome Research Institute at
Verma, P.S. & Agarwal, V.K. (2003). Cell Biology, Genetics, Molecular Biology, Evolution and Ecology. S. Chand & Co. New Delhi: India