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APPLICATIONS OF BLOOD GROUP SYSTEMS AND DNA FINGERPRINTINGS

ARISE, R. O. (Ph. D)Department of Biochemistry,University of Ilorin, Ilorin, Nigeria

INTRODUCTIONBlood is the red viscid fluid filling the heart and blood vessels. It consists of a

colourless fluid, known as the plasma, in which are suspended the red blood cells orerythrocytes, the white cell or leucocytes, and the platelets, or thromobocytes. Theplasma contains a great many substances in solution including factors which enable theblood to clot. The normal composition of blood is 55% plasma and 45% cells. The redblood cells are small, flat and plate-like in shape, with a rim round the edge, and a hollowin the middle. In each cubic millimeter of blood, there are approximately 5.5 million redblood cells (RBC). The RBC does not have a nucleus. The life of a red blood cell is aboutfour months. The blood provides a transport system connecting all parts of the body withall cells in the tissues. The blood transports oxygen from the lungs to all parts of thebody. It also transports digested food particles such as amino acids and glucose to theliver and consequently to the circulatory system. The blood also helps to transportexcretory products such as water, carbon dioxide, and urea.

Blood group is a characteristic of an individual's red blood cells, defined in terms ofspecific substances (carbohydrates and proteins) on the cell membrane while DNAfingerprinting is a very quick way to compare shorter DNA sequence of any two livingorganisms. More realistically, knowledge of DNA sequences and blood groups can proveuseful in identification projects. These include reuniting families torn apart by war or bythe actions of repressive regimes, identifying corpses, checking paternity, and mostcommonly, investigating and prosecuting crimes. Forensic uses of blood groupings andDNA finger printing technology inspires great hope but arouses considerablecontroversy.BLOOD GROUP SYSTEMS

The two most important classifications to describe blood types in humans are ABOand the Rhesus factor (Rh factor). There are 46 other known types (antigens) in humans,most of which are much rarer than ABO and Rh. Blood transfusions from incompatiblegroups can cause an immunological transfusion reaction, resulting in hemolytic anemia,renal failure, shock, and death. When a patient has suffered a severe loss of blood, ablood transfusion is given to make up the quantity of blood lost. Blood transfusion is theintravenous replacement of lost or destroyed blood by compatible citrated human blood.The blood given in the transfusion must be of the correct type, called a BLOOD GROUP;otherwise the tissues reject the new blood by forming a clot. Tissues generally reject anyforeign body (antigen) and a transfusion of blood can, if of the wrong groups, be taken asan antigen. The ABO blood types also exist among chimpanzees and bonobos. Bloodtype is determined by the antigens (epitopes) on the surface of a red blood cell. Some ofthese are proteins, while others are proteins with polysaccharides attached. The absence

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of some of these markers leads to production of antibodies against this marker.Administration of the wrong blood type would lead to immediate destruction of theinfused blood. The breakdown products cause acute medical illness; hence, it is of, quiteliterally, vital importance that the blood types of the donor and receptor are properlymatched.

Austrian scientist Karl Landsteiner is widely credited with the discovery of themain blood type system (ABO) in 1901; he was awarded the Nobel Prize in Physiologyor Medicine in 1930 for his work. Landsteiner described A, B, and O. Landsteinerand Wiener also discovered the second most important antigen set, the Rhesus system, in1937. It is named after the Rhesus monkey, in which the factor was first identified byKarl Landsteiner and Wiener. The phrases "blood group" and "blood type" are often usedinterchangeably, although this is not technically correct. "Blood group" is used to referspecifically to a person's ABO status, while "blood type" refers to both ABO and Rhfactors.THE ABO SYSTEM

There are four groups in the ABO blood grouping system; they include bloodgroup A, B, AB and O. The cells of these groups contain the correspondingantigens, A, B, & A and B except group O cells which contain neither antigen A nor B.In the plasma there are agglutinins which will cause agglutination of any cell carrying thecorresponding antigen.Blood group A: This group contains antigen A in their blood cells and antibody anti-B in

their plasma. People with blood group A can receive and give blood to peoplewith blood group A only (provided they are compatible for Rh factor).

Blood Group B: This group contains antigen B in their blood cells and antibody anti-Ain their plasma. People with blood group B can receive and give blood to peoplewith blood group B only (provided they are compatible for Rh factor)

Blood Group AB: This group contains both antigens A and B in their blood cells andnone of the antibodies in their plasma. People with blood group AB are knownas universal recipients as they can receive blood from any person belonging toany of the ABO group (with matching rhesus status). Thus people with AB bloodtype can receive blood from people with blood group A, B, AB or O(however, compatibility with other antigens like rhesus needs to be matched).

Blood Group O: This group contains none of the antigen (A or B in their blood cellsbut contain both the antibodies (anti A and anti-B) in their plasma. People withblood group O are known as universal donors as they can donate their bloodto a person belonging to any of the ABO group (with matching rhesus status).Thus people with O blood type can donate blood to people with blood groupA, B AB or O (however, compatibility with other antigens like rhesusneeds to be matched).Overall, the O blood type is the most common blood type in the world, although

in some areas, such as Sweden and Norway, the A group dominates. The A antigen isoverall more common than the B antigen. Since the AB blood type requires thepresence of both A and B antigens, the AB blood type is the rarest of the ABO bloodtypes. There are known racial and geographic distributions of the ABO blood types.

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According to Benes in 1993, it can be partly attributed to the relation among blood typesand particular illnesses: apparently, certain blood types give greater (or lesser) resistanceto various diseases. For instance, type O people have lessened resistance to the BlackPlague, and therefore type O is less common in European populations. This ABOgrouping system is determined by testing a suspension of red cells with anti-A and anti-Bserum or testing serum with known cells.

THE RHESUS BLOOD GROUPIn rhesus blood grouping, the red cells contain four pairs of antigens which are

known by the letters Cc, Dd, Ee and Ff. The letters denote allelomorphic genes whichare present in all cells except the sex cells where a chromosome can carry C or c, but notboth. In this way, the Rhesus genes and blood groups are derived equally from eachparent. When the cells contain only the cde groups, then the blood is said to be Rhesusnegative (Rh -ve); when the cells contain C, D or E singly or in combination with cde,then the blood is Rhesus positive (Rh +ve). These groups are antigenic and can, undersuitable conditions produce the corresponding antibody in the serum. These antibodiesare then used to detect the presence of Rh groups in cells. Matching the Rhesus factor isvery important, as mismatching (an Rh positive donor to an Rh negative recipient) maycause the production in the recipient of an antibody to the Rh(D) antigen, which couldlead to subsequent haemolysis. This is of particular importance in females of or belowchildbearing age, where any subsequent pregnancy may be affected by the antibodyproduced. For one-off transfusions, particularly in older males, the use of Rh(D) positiveblood in an Rh(D) negative individual (who has no atypical red cell antibodies) may beindicated if it is necessary to conserve Rh(D) negative stocks for more appropriate use.The converse is not true: Rh +ve patients do not react to Rh -ve blood.

Rh disease occurs when an Rh negative mother who has already had an Rhpositive child (or an accidental Rh +ve blood transfusion) carries another Rh positivechild. After the first pregnancy, the mother develops IgG antibodies against Rh +ve redblood cells, which can cross the placenta and hemolyse the red cells of the second child.This reaction does not always occur, and is less likely to occur if the child carries eitherthe A or B antigen and the mother does not. In the past, Rh incompatibility couldresult in stillbirth, or in death of the mother, or both. Rh incompatibility was untilrecently the most common cause of long term disability in the United States. At first, thiswas treated by transfusing the blood of infants who survived. At present, it can be treatedwith certain anti-Rh +ve antisera, the most common of which is Rhogam (anti-D). It canbe anticipated by determining the blood type of every child of an RhD -ve mother; if it isRh +ve, the mother is treated with anti-D to prevent development of antibodies againstRh +ve red blood cells.USES OF ABO AND RHESUS BLOOD GROUPS

a. TransfusionThe blood donated by healthy persons is tested to ensure that the level of hemoglobin

is satisfactory and that there is no risk of transmitting certain diseases, such as AIDS or

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hepatitis. It is then fractionated (split) into its component parts, particularly red cells,plasma, and platelets. Correct matching for the ABO system is vital. The most importantblood group systems for transfusion of red cells are ABO and Rh. Persons who haveeither of the red cell antigens (A and B) have antibody present in their serum of the typethat will oppose an antigen of its opposite nature; for example, group A blood containsA antigens on red cell surfaces and anti-B antibodies in the surrounding serum. On theother hand, O group individuals lack both the A and the B antigen and thus have bothanti-A and anti-B in their serum. If these antibodies combine with the appropriateantigen, the result is hemolytic transfusion reaction and possibly death. Red celltransfusions must therefore be ABO compatible. The blood groups A and B have varioussubgroups (e.g., A1, A2, A3, and B1, B2, and B3). The only common subgroups that arelikely to affect red cell transfusions are the subgroups of A.

Potential donors are also tested for some of the antigens of the Rh system, since it isessential to know whether they are Rh-positive or Rh-negative. Rh-negative indicates theabsence of the D antigen. Rh-negative persons transfused with Rh-positive blood willmake anti-D antibodies from 50 to 75 percent of the time. Antibody made in response toa foreign red cell antigen is usually not harmful but does require subsequent transfusionsto be antigen-negative. Rh-positive blood should never be given to Rh-negative femalesbefore or during the childbearing age unless Rh negative blood is not available and thetransfusion is lifesaving. If such a woman subsequently became pregnant with an Rh-positive fetus, she might form anti-Rh antibody, even though the pregnancy was the first,and the child might develop erythroblastosis fetalis (hemolytic disease of the newborn).

b. Organ transplantsThe ABO antigens are widely distributed throughout the tissues of the body.

Therefore, when organs such as kidneys are transplanted, most surgeons prefer to useorgans that are matched to the recipient's with respect to the ABO antigen system,although the occasional survival of a grafted ABO-incompatible kidney has occurred.The remaining red cell antigen systems are not relevant in organ transplantation.

c. Paternity testingAlthough blood group studies cannot be used to prove paternity, they can provide

unequivocal evidence that a male is not the father of a particular child. Since the red cellantigens are inherited as dominant traits, a child cannot have a blood group antigen that isnot present in one or both parents. For example, if the child in question belongs to groupA and both the mother and the putative father are group O, the man is excluded frompaternity. Furthermore, if one parent is genetically homozygous for a particularantigenthat is, has inherited the gene for it from both the grandfather and grandmotherof the childthen that antigen must appear in the blood of the child. For example, on theMN system, a father whose phenotype is M and whose genotype is MM (in other words, aman who is of blood type M and has inherited the characteristic from both parents) willtransmit an M allele to all his progeny. In medicolegal work it is important that the blood

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samples are properly identified. By using multiple red cell antigen systems and addingadditional studies on other blood types (HLA [human leukocyte antigen], red cellenzymes, and plasma proteins), it is possible to state with a high degree of statisticalcertainty that a particular male is the father.

d. Blood groups and diseaseIn some cases an increased incidence of a particular antigen seems to be associated

with a certain disease. Stomach cancer is more common in people of group A than inthose of groups O and B. Duodenal ulceration is more common in nonsecretors of ABHsubstances than in secretors. For practical purposes, however, these statistical correlationsare unimportant. There are other examples that illustrate the importance of blood groupsto the normal functions of red cells.DNA FINGERPRINTING TECHNOLOGY

Each person has a unique DNA fingerprint like the fingerprints that came into useby detectives and police laboratory during the 1930s. Unlike conventional finger printthat occurs only on the finger tips and can be altered by surgery, a DNA fingerprint is thesame for every cell, tissue, and organ of a person. It cannot be altered by any knowntreatment. Consequently, DNA fingerprinting is rapidly becoming the primary method foridentifying and distinguishing among individual human beings.

The characteristics of all living organisms including humans are essentiallydetermined by information contained within DNA (deoxyribonucleic acid) that theyinherit from their parents. The molecular structure of DNA can be imagined as a zipperwith each tooth represented by one of four letters (A, C, G or T), and with opposite teethforming one or two pairs, either A-T or G-C. The letters A, C, G and T stand for adenine,cytosine, guanine and thymine, the basic building blocks of DNA

The information contained in DNA is determined primarily by the sequence ofletters along the zipper. For example, the sequence ACGCT represents differentinformation than the sequence AGTCC in the same way that the word POST has adifferent meaning from STOP or POTS, even though they use the same letters. Thetraits of a human being are the result of information contained in the DNA code.

The chemical structure of everyones DNA (or any animal) is the order of thebase pairs. There are so many million of base pairs in each persons DNA that everyperson has different sequence. Using these sequences, every person could be identifiedsolely by the sequence of their base pairs. However, because there are also many millionsof base pairs, the task would be very time-consuming. Instead, scientists are able to use ashorter method, because of repeating patterns in DNA. These patterns do not, however,give an individual fingerprint, but they are able to determine whether two DNAsamples are from the same person, related people, or non-related people.

Living organisms that look different or have different characteristics also havedifferent DNA sequence. The more varied the organisms, the more varied the DNAsequences. DNA fingerprinting is a very quick way to compare shorter DNA sequence ofany two living organisms. DNA fingerprinting is a laboratory procedure that requires sixsteps:

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1. Isolation of DNA: DNA must be recovered from the cells or tissues of the body.Only a small amount of tissue, (blood, hair, or skin) is needed. For example theamount of DNA found at the root of one hair strand is usually sufficient.

2. Cutting, sizing and sorting: Special enzymes called restriction enzymes are usedto cut the DNA at specific places. For example, an enzyme called EcoR1, foundin bacteria, will cut DNA only when the sequence GAATTC occurs. The DNApieces are sorted according to size by a sieving technique called electrophoresis.The DNA pieces are passed through a gel made from seaweed agarose (a jelly-like product made from seaweed).

3. Transfer of DNA to nylon: The distribution of DNA pieces is transferred to anylon sheet by placing the sheet on the gel and soaking them overnight.

4. Probing: A radioactive genetic probe is used in a hybridization reaction with theDNA in question.

5. Probing: Adding radioactive or coloured pobes to the nylon (nitrocellulose paper)sheet produces a pattern called the DNA fingerprint. Each probe typically sticksin only one or two specific places on the nylon sheet.

6. DNA fingerprint: The final DNA fingerprint is built by using several probes (5-10 or more) simultaneously.USES OF DNA FINGERPRINTS

DNA fingerprints are useful in several applications of human health careresearch and the justice system:

a) Diagnosis of inherited disorder: DNA fingerprinting is used to diagnoseinherited disorders in both parental and newborn babies in hospitals around theworld. These disorders may include cystic fibrosis, hemophilia, sickle cellaenemia and others. Early detection of such disorders enables medical practionersand the parents for proper treatment of the child. Genetic counselors use DNAfingerprint information to help prospective parents understand the risks of havingan affected child and in their decision concerning affected pregnancies as well asmarriages.

b) Developing cures for inherited disorders: Research programmes aimed atlocating inherited disorders on the chromosomes depend on the informationcontained in DNA fingerprint. By studying the DNA fingerprints of relatives whohave history of some particular disorder, or by comparing larger groups of peoplewith and without the disorder, it is possible to identify DNA patterns associatedwith the disease in question. This is a necessary first step in designing andeventual genetic cure for these disorders

c) Paternity and maternity: Because a person inherits his or her variable numbertandem repeats (VNTRs) from his/her parents, VNTR patterns can be used toestablish paternity and maternity. The patterns are so specific that a parentalVNTR pattern can be reconstructed even if only the childrens VNTR patterns areknown.

d) Criminal identification and forensic: DNA isolated from blood, hair, skin, cellsor other genetic evidence left at the scene of crime can be compared, throughVNTR patterns, with the DNA of a criminal suspect to determine guilt or

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innocence. VNTR patterns are also useful in establishing identity of a homicidevictim, either from DNA found as evidence or from the body itself.

e) Personal identification: The notion of using DNA fingerprints as a sort ofgenetic bar code to identify individuals is likely to happen anytime in the nearestfuture. The technology required to isolate, keep on file, and then analyze millionof much specified VNTR patterns is both expensive and impractical.CONCLUSION

The successful applications of blood groups and DNA finger prints wouldchange the relations between criminals and victims in unpredictable ways.Obviously, adding a powerful new weapon to the arsenal of the law will increaserate of detection and conviction, removing dangerous people from circulation-and, we should remember, it will also prove valuable in clearing the innocent. Yetit will be naive to think that criminals will remain passive in the face of the newtechnology, or that the prospect of inevitable capture and incarceration will staytheir hands. Helpful though blood groupings and DNA finger prints may be, it isnot a panacea.ReferencesAgre, P and Carton, J.P. (1991): Molecular biology of the Rh antigens. Blood78:551-563.Avent, N.D., Liu, W. and Warner, K.M. (1996): Immunochemical Analysis of thehuman erythrocyte Rh polypeptide. J. Biol. Chem. 271: 14233- 14239.Landsteiner, K. and Wiener, A.S. (1940): An agglutinable factor in human bloodrecognized by immune sera for rhesus blood. Proc. Soc. Exp. Biol. Med. 43:223-224.