GENETICS OF HUMAN BLOOD TYPE Introduction The genetics of blood types is relatively simple when considering any one blood protein. However, the complexity increases when one considers all the different proteins associated with the surface of a red blood cell (RBC). Three of the most common blood typing systems (or groups) are the ABO, Rh, and MN systems (note: there are additional systems). In the ABO system, one locus with three possible alleles (I A, I B, i) determines the genotype of an individual. I A and I B are codominant to each other. Each is dominant to the i allele. Each allele determines the presence of a particular protein on the surface of a RBC. For example, the I A allele will produce a functional A protein. The presence of the i allele indicates the presence of a nonfunctional surface protein. Individuals that are genotypically ii will have type O blood and, thus, neither the A nor the B proteins on the surfaces of their RBCs. The proteins located on the surface of RBCs act as antigens (sometimes referred to as surface antigens). If they are introduced into an individual who does not produce that same surface antigen(s), the recipients immune system will recogize the protein(s) as a foreign substance and use specific antiboides (produced by the immune system) to neutralize it (e.g. remove or destroy it). Table 1 below summarizes the various surface antigen and antibody characteristics within the ABO blood group system. Table 1. The ABO Blood Types Blood Phenotype Blood Genotype Surface Antigen Present Antibody That Recognizes the Antigen Antibodies Typically Present in the Blood A I A I A or I A i A anti-a anti-b B I B I B or I B i B anti-b anti-a AB I A I B A & B anti-a & anti-b none O ii None None anti-a & anti-b The Rh system is simpler, with only two alleles. The dominant allele (D) means that the RBCs will have the Rh antigen on their surface (i.e. they are Rh+). The recessive allele (d) means that they will not have the Rh antigen on the surface of their RBCs (i.e. they are Rh). Table 2 below summarizes the characteristics of the various types of the Rh system. 27
Table 2. The Rh Blood Group System Phenotype Genotype RBC Surface Antigen Antibodies Present in Blood Rh+ DD or Dd Rh none Rh- dd no Rh anit-rh The genetic basis for the MN system is also simple, consisting of two alleles (L M and L N ). Each allele results in the production of an RBC surface antigen (M or N, respectively), resulting in three possible phenotypes (MM, NN, and MN). Red blood cells can be typed by reacting them with various types of antisera, each specific for/recognizing a single RBC antigen. If the cells agglutinate (form granular clumps) when reacted with a particular antibody, then that indicates the presence of that particular antigen on the surfaces of the RBCs. One use of these immunoagglutination reactions is the determination of parentage. For example, when a mother sues a potential father for child support blood types can be used to eliminate genetically incompatible individuals and can suggest genetically compatible individuals as possible fathers. The greater the number of different blood type antigens analyzed, the greater the probability of eliminating all non-fathers and thereby establishing paternity with a reasonable degree of accuracy. Blood types have also been used to establish parentage when mixups have occurred in hospital nurseries. This lab exercise involves two separate activities that require you to utilize blood type genetics. In Part A you will resolve a hospital mixup by typing blood samples from two unwed mothers and their three children. Part B will employ blood type genetics to determine paternity by typing blood samples from a mother, her daughter, and two potential fathers. A. Maternity Testing In this investigation you will analyze the blood types of two unwed mothers and three children. With the data you will determine which children are fraternal twins and which children belong to which mother. In the wee hours of the morning, Opal had a set of fraternal twins and Abby gave birth to her first child. It is now two years later and Abby is claiming that the hospital sent her home with the wrong child and that her baby was given to someone else (Opal). You must determine the blood types of Opal, Abby, and the three children in order to straighten out this mess. Opal was sent home with babies #1 and 2. Abby was sent home with baby #3. Procedure 1. You will need the following materials: 5 blood test plates OR plastic trays with 10 wells 10 mixing sticks/ tooth picks 28
Anti-A serum (blue) and Anti-B serum (yellow) Blood samples: Opal, Abby, Baby #1, Baby #2, Baby #3 2. Each well will be used only once. Label each plate (or tray) with the individual to be tested. 3. Put a drop of anti-a serum in the appropriate well on each plate/tray. 4. Put a drop of anti-b serum in the appropriate well on each plate/tray. 5. Put a drop of Opal's blood in the appropriate wells on her plate/tray. 6. Put a drop of Abby's blood in the appropriate wells on her plate/tray. 7. Put a drop of Baby #1's blood in the appropriate wells on his/her plate/tray. 8. Put a drop of Baby #2's blood in the appropriate wells on his/her plate/tray. 9. Put a drop of Baby #3's blood in the appropriate wells on his/her plate/tray. 10. Mix the blood and serum with separate sticks. Mix until the surface tension allows the blood and serum to spread evenly over the support surface. 11. Gently rock the plates for 1-2 minutes. 12. Record the results for each individual as yes (agglutination) or no (no agglutination) in the table below. NOTE: IT MAY BE NECESSARY TO VIEW REACTION UNDER A MICROSCOPE (AGGLUTINATION MAY NOT BE VISIBLE TO THE NAKED EYE). IF THIS IS THE CASE, REACTIONS MUST BE PERFORMED ON MICROSCOPE SLIDES. Anti-A Anti-B Opal Abby Baby #1 Baby #2 Baby #3 B. Paternity Testing In this investigation you will determine the blood types of Betty (the mother), Abby (the daughter), and 3 potential fathers (Father #1, Father #2, Father #3). You will use the data obtained to identify Abby s father. 29
Procedure 1. You will need the following materials: 5 blood test plates OR a plastic trays) with 15 wells total 15 mixing sticks/tooth picks Anti-A serum (blue) Anti-B serum (yellow) Anti-Rh serum (colorless) Blood samples: Betty, Abby, Father #1, Father #2, Father #3 2. Each plate/tray will be used to type one of the blood samples. Label each plate with the individual to be tested. 3. Put a drop of anti-a serum in the appropriate well of each plate. 4. Put a drop of anti-b serum in the appropriate well of each plate. 5. Put a drop of anti-rh serum in the appropriate well of each plate. 6. Put a drop of Betty's blood in each of the 3 wells on her plate. 7. Put a drop of Abby's blood in each of the 3 wells on her plate. 8. Put a drop of Father #1's blood in each of the 3 wells of his plate. 7. Put a drop of Father #2's blood in each of the 3 wells of his plate. 8. Put a drop of Father #3's blood in each of the 3 wells of his plate. 10. Mix the blood and serum with separate sticks. Mix until the surface tension allows the blood and serum to spread evenly over the support surface. 11. Gently rock the cards/plates for 1-2 minutes. NOTE: Agglutination of RBCs with anti-rh serum often requires a longer incubation (3 5 minutes). 12. Record the results for each individual as yes (agglutination) or no (no agglutination in the table below. Note: it may be necessary to view reaction under a microscope (agglutination may not be visible to the naked eye). If this is the case, reactions must be performed on microscope slides. Anti-A Anti-B Anti-Rh Betty Abby Father #1 Father #2 Father #3 30
A. Maternity Testing - answer the following questions: 1. What is Opal's blood type (i.e. phenotype)? 2. What is Abby's blood type? 3. What are the blood types of the 3 children? Baby #1: Baby #2: Baby #3: 4. What ABO gene(s) could Opal give to her children? (use proper numenclature) 5. What ABO gene(s) could Abby give her children? (use proper nomenclature) 6. Which blood samples are from Opal's twins? Explain. 7. Which blood sample is from Abby's child? Explain. 8. There are two potential fathers for Opal's twins. Lewis's blood type is type A, while Ben's blood type is AB. Which alleged father is the father of Opal's twins? Explain. 31
B. Paternity Testing - answer the following questions: 1. What is Betty's blood type? 2. What is Abby's blood type? 3. What are the blood types of the 3 potential fathers? Father #1: Father #2: Father #3: 4. What ABO gene(s) did Abby receive from her mother? Explain. 5. What ABO gene(s) did Abby receive from her father? Explain. 6. Which, if any, of the potential fathers can be eliminated based on the ABO results? Explain. 7. Rh+ individuals can be homozygous (DD) or heterozygous (Dd), while Rhindividuals must be homozygous recessive (dd). Based on this information, what Rh gene did Abby receive from her mother? Explain. 8. What Rh gene did Abby receive from her father? 9. Which, if any, of the potential fathers can be eliminated on the basis of the Rh type? Explain. 10. Which alleged father, if any, is a good candidate for paying child support for Abby? 32