The Blood Group Systems Inheritance and Genetics Nawsherwan sadiq 2012-2013
•The blood group you belong to depends onwhat you have inherited from your parents.
• There are more than 20 genetically determinedblood group systems known today• The AB0 and Rhesus (Rh) systems are themost important ones used for blood transfusions.• Not all blood groups are compatible with eachother. Mixing incompatible blood groups leads toblood clumping or agglutination, which isdangerous for individuals.
AB0 blood grouping system Blood group A If you belong to the blood group A, you have A antigens on the surface of your RBCs and B antibodies in your blood plasma. Blood group B If you belong to the blood group B, you have B antigens on the surface of your RBCs and A antibodies in your blood plasma.
Blood group ABIf you belong to the blood groupAB, you have both A and Bantigens on the surface of yourRBCs and no A or B antibodiesat all in your blood plasma.Blood group OIf you belong to the blood group O,you have neither A or B antigens onthe surface of your RBCs but you haveboth A and B antibodies in your bloodplasma.
• The "A“ and "B" antigens are also producedby some other plants and microorganisms.Thus, individuals who do not recognize one ormore of these antigens as "self" will produceantibodies against the plant or microbialantigens.• These antibodies will also react with humanantigens of the same kind whether introducedvia a blood transfusion or a tissue graft.
Inheritance of ABO GroupsAllele from Allele from Genotype of Blood types ofthe mother the father offspring offspring A A AA A A B AB AB A O AO A B A AB AB B B BB B B O BO B O O OO O 7
ABO Typing• Cell Group • Reverse Group – Test Washed Cells – Test plasma/serum With: with: – Monoclonal Anti-A – Known A1 cells – Known B cells – Monoclonal Anti-B – Known O cells – Inert control – ? Known A2 cells• Agglutination is a • Reactions may be positive result weaker than cell group 8
Significance of ABO Group• ABO mismatched transfusions: – Rare – May be life threatening – Can be caused by technical or clerical error – Intravascular haemolysis – More severe in group O patients 9
The Rh(D) Antigen• RH is the most complex system, with over 45 antigens• Discovered in 1940 after work on Rhesus monkeys• Subsequently discovered to be unrelated to monkeys• RH gene located on short arm of chromosome 1 10
Simple Genetics of Rh(D)• 86% of caucasians are Rh(D) pos• The antigen d has not been found• The d gene is recessive: – Dd, dD, DD, persons are Rh(D) pos – Only dd persons are Rh(D) neg 11
Distribution of Rh(D) TypesPopulation Rh(D) pos Rh(D) negCaucasian 86% 14% African- 95% 5%American Oriental >99% <1% 12
Significance of Rh(D)• 80% of Rh(D) neg persons exposed to Rh(D) pos blood will develop anti-D• Anti-D can also be stimulated by pregnancy with an Rh(D) positive baby – Sensitisation can be prevented by the use of anti-D immunoglobulin, antenatally and post natally• Rh(D) neg females of childbearing potential should never be given Rh(D) positive blood products 13
Inheritance• ABO & RH genes are not linked• ABO & Rh(D) type are inherited independentlyFor example: An A Rh(D) pos mother and a B Rh(D) pos father could have an O Rh(D) neg child ABO & Rh(D) 14
Inheritance of ABO and Rh(D) Mother Father Group A AO Group B BO Rh(D) pos Dd Rh(D) pos DdGroup A AO Group B BO Group O OORh(D) pos Dd Rh(D) pos Dd Rh(D) neg dd 15
ABO inheritance and genetics • The ABO gene is autosomal (the gene is not on either sex chromosomes) • The ABO gene locus is located on the chromosome 9.• A and B blood groups are dominant over the O blood group• A and B group genes are co-dominant• Each person has two copies of genes coding for their ABO bloodgroup (one maternal and one paternal in origin)
Principles of Heredity• Antigens and enzymes are genetically controlled – Genes: responsible for transfer of hereditable material – Genes are found on chromosomes, which are found in the nucleus of every cell• Human Cells contain 46 chromosomes with the exception of the egg and sperm, which contain only 23. – 23 of these chromosomes are inherited from mother – 23 of these chromosomes are inherited from father
Genes Come in Pairs• The position a gene occupies on a chromosome is called a locus.• Genes for the same trait are located at the same locus on both the mother and the father’s chromosomes.• Alternative forms of genes that influence a given characteristic are called alleles. – Father: allele for brown eyes – Mother: allele for blue eyes
Blood Types are Genetic• A and B Blood Types are Dominant – Dominant: Characteristic is shown• Blood Type O is Recessive – Recessive: Characteristic is hidden – Recessive characteristics only appear when both alleles are recessive • Homozygous recessive OO
Phenotype V. Genotype• Phenotype: individual’s outward characteristics• Genotype: individual’s pair of allele genes together• Example: – Phenotype Genotype Type B Blood Could be BO or BB depending on parents
Important Parts for Forensic Science• Red Blood Cells—because of their importance in blood typing• Serum—because of its’ importance in carrying antibodies
• The term serology refers to a broad scope of laboratory tests that use specific antigen and serum antibody reactions.• Blood typing falls into this category.
ABO and H Antigen Genetics• Genes at three separate loci control the occurrence and location of ABO antigens• The presence or absence of the A, B, and H antigens is controlled by the H and ABO genes
Location• The presence or absence of the ABH antigens on the red blood cell membrane is controlled by the H gene• The presence or absence of the ABH antigens in secretions is indirectly controlled by the Se gene
ABO Antigen Genetics• H gene – H and h alleles (h is an amorph)• Se gene – Se and se alleles (se is an amorph)• ABO genes – A, B and O alleles
H Antigen• The H gene codes for an enzyme that adds the sugar fucose to the terminal sugar of a precursor substance (PS)• The precursor substance (proteins and lipids) is formed on an oligosaccharide chain (the basic structure)
Formation of the H antigen RBC GlucoseH antigen Galactose N-acetylglucosamine Galactose Fucose
H antigen• The H antigen is the foundation upon which A and B antigens are built• A and B genes code for enzymes that add an immunodominant sugar to the H antigen – Immunodominant sugars are present at the terminal ends of the chains and confer the ABO antigen specificity
A and B Antigen• The ―A‖ gene codes for an enzyme (transferase) that adds N-acetylgalactosamine to the terminal sugar of the H antigen – N-acetylgalactosaminyltransferase• The ―B‖ gene codes for an enzyme that adds D- galactose to the terminal sugar of the H antigen – D-galactosyltransferase
Formation of the A antigen RBC Glucose Galactose N-acetylglucosamine Galactose N-acetylgalactosamine Fucose
Formation of the B antigen RBC Glucose Galactose N-acetylglucosamine Galactose Galactose Fucose
Genetics• The H antigen is found on the RBC when you have the Hh or HH genotype, but NOT from the hh genotype• The A antigen is found on the RBC when you have the Hh, HH, and A/A, A/O, or A/B genotypes• The B antigen is found on the RBC when you have the Hh, HH, and B/B, B/O, or A/B genotypes
A A A A Group O Group A Many H Fewer Aantigen sites H antigen sites Most of the H antigen sites in a Group A individual have been converted to the A antigen
ABO Antigens in Secretions• Secretions include body fluids like plasma, saliva, synovial fluid, etc• Blood Group Substances are soluble antigens (A, B, and H) that can be found in the secretions. This is controlled by the H and Se genes
Secretor Status• The secretor gene consists of 2 alleles (Se and se)• The Se gene is responsible for the expression of the H antigen on glycoprotein structures located in body secretions• If the Se allele is inherited as SeSe or Sese, the person is called a ―secretor‖ – 80% of the population are secretors
Secretors• Secretors express soluble forms of the H antigen in secretions that can then be converted to A or B antigens (by the transferases)• Individuals who inherit the sese gene are called ―nonsecretors‖ – The se allele is an amorph (nothing expressed) – sese individuals do not convert antigen precursors to H antigen and has neither soluble H antigen nor soluble A or B antigens in body fluids
Secretor Status Summary• The Se gene codes for the presence of the H antigen in secretions, therefore the presence of A and/or B antigens in the secretions is contingent on the inheritance of the Se gene and the H gene A antigenSe gene (SeSe H antigen in and/or or Sese) secretions B antigense gene (sese) No antigens secreted in saliva or other body fluids
ABO Subgroups• ABO subgroups differ in the amount of antigen present on the red blood cell membrane – Subgroups have less antigen• Subgroups are the result of less effective enzymes. They are not as efficient in converting H antigens to A or B antigens (fewer antigens are present on the RBC)• Subgroups of A are more common than subgroups of B
Subgroups of A• The 2 principle subgroups of A are: A1 and A2 – Both react strongly with reagent anti-A – To distinguish A1 from A2 red cells, the lectin Dolichos biflorus is used (anti-A1) – 80% of group A or AB individuals are subgroup A1 – 20% are A2 and A2B
A2 Phenotype• Why is the A2 phenotype important? – A2 and A2B individuals may produce an anti-A1 – This may cause discrepancies when a crossmatch is done (incompatibility)• What’s the difference between the A1 and A2 antigen? – It’s quantitative – The A2 gene doesn’t convert the H to A very well – The result is fewer A2 antigen sites compared to the many A antigen sites
A1 and A2 Subgroups* Anti-A Anti-A1 Anti-H ABO # of antisera antisera lectin antibodies antigen in serum sites per RBCA1 4+ 4+ 0 Anti-B 900 x103A2 4+ 0 3+ Anti-B & 250 x103 anti-A1 *Adapted from Flynn, J. (1998). Essentials of Immunohematology
Other A subgroups• There are other additional subgroups of A – Aint (intermediate), A3, Ax, Am, Aend, Ael, Abantu• A3 red cells cause mixed field agglutination when polyclonal anti-A or anti-A,B is used• Mixed field agglutination appears as small agglutinates with a background of unagglutinated RBCs• They may contain anti-A1
B Subgroups• B subgroups occur less than A subgroups• B subgroups are differentiated by the type of reaction with anti-B, anti-A,B, and anti-H• B3, Bx, Bm, and Bel
Landsteiner’s Rule:• Normal, Healthy individuals possess ABO antibodies to the ABO antigen absent from their RBCs
Blood Group Systems• Most blood group systems (ABO and others) are made up of: – An antigen on a red cell and the absence of it’s corresponding antibody in the serum (if you’re A, you don’t have anti-A)• If you do NOT have a particular antigen on your red cells then it is possible (when exposed to foreign RBCs) to illicit an immune response that results in the production of the antibody specific for the missing antigen
ABO• Remember: – The ABO Blood Group System does NOT require the presence of a foreign red blood cell for the production of ABO antibodies – ABO antibodies are ―non-red blood cell stimulated‖ probably from environmental exposure and are referred to as ―expected antibodies‖
Anti-A1• Group O and B individuals contain anti-A in their serum• However, the anti-A can be separated into different components: anti-A and anti-A1• Anti-A1 only agglutinates the A1 antigen, not the A2 antigen• There is no anti-A2.
Anti-A,B• Found in the serum of group O individuals• Reacts with A, B, and AB cells• Predominately IgG, with small portions being IgM• Anti-A,B is one antibody, it is not a mixture of anti-A and anti-B antibodies
ABO antibodies• IgM is the predominant antibody in Group A and Group B individuals – Anti-A – Anti-B• IgG (with some IgM) is the predominant antibody in Group O individuals – Anti-A,B (with some anti-A and anti-B)
ABO antibody facts• Reactions phase: Room temperature• Complement can be activated with ABO antibodies (mostly IgM, some IgG)• High titer: react strongly (4+)
ABO Antibodies• Usually present within the first 3-6 months of life• Stable by ages 5-6 years• Decline in older age• Newborns may passively acquire maternal antibodies (IgG crosses placenta) – Reverse grouping (with serum) should not be performed on newborns or cord blood
Paternity Tests• No blood group can be present in a child without being present in one of the parents• Paternity tests can be resolved in this way unless disputed fathers have the same blood type• Paternity tests can also be determined by using DNA testing
Blood as Evidence• Blood typing not so useful anymore because of DNA technology• Scientists can now characterize biological evidence by selecting regions of our DNA
AUTOSOMAL CHROMOSOME The alleles for Blood group are in the same A place on the B chromosome 9. However the genes have a different code giving the different blood group DadMom
What do co-dominant genes mean?This meant that if a person inherited one A group gene and oneB group gene their red cells would possess both the A and Bblood group antigens.These alleles were termed A ( which produced the A antigen ),B (which produced the B antigen) and O (which was "nonfunctional"and produced no A or B antigen)
Possible Blood group GenotypesParent A B OAlleleABO
Possible Blood group GenotypesParent A B OAlleleA AA AB AOB AB BB BOO AO BO OO
The ABO blood groups• The most important in assuring a safe blood transfusion.• The table shows the four ABO phenotypes ("blood groups") presentin the human population and the genotypes that give rise to them. Blood Antigens Antibodies in Serum Genotypes Group on RBCs A A Anti-B AA or AO B B Anti-A BB or BO AB A and B Neither AB O Neither Anti-A and anti-B OO
The ABO Blood Group SystemLaboratory Determination of the ABO System
Several methods for testing the ABO group of anindividual exist. The most common method is:Serology: This is a direct detection of the ABOantigens. It is the main method used in bloodtransfusion centres and hospital blood banks.This form of testing involves two components:a) Antibodies that are specific at detecting aparticular ABO antigen on RBCs.b) Cells that are of a known ABO group thatare agglutinated by the naturally occurringantibodies in the persons serum.
• Illustration of the forward and reversegrouping reaction patterns of the ABOgroups using a blood group tile
When RBCs carrying one or both antigens are exposed to thecorresponding antibodies, they agglutinate; that is, clumptogether. People usually have antibodies against those red cellantigens that they lack. Human RBC before (left) and after (right) adding serum containing anti-A antibodies. The agglutination reaction reveals the presence of the A antigen on the surface of the cells.
Blood Antigens Antibodies Can give CanGroup blood to receive blood from AB A B O
Blood Antigens Antibodies Can give CanGroup blood to receive blood from AB A and B None AB AB, A, B, O A A B A and AB A and O B B A B and AB B and O O None A and B AB, A, B, O O
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