Review your ability to understand inheritance of blood types with the worksheet and quiz. A couple of the quiz questions will test your knowledge of the number of alleles that exist for blood types in addition to asking you to identify a blood type that reflects codominance.
Blood Type And Inheritance Homework Answers
The discovery of the ABO blood group, over 100 years ago, caused great excitement.Until then, all blood had been assumed to be the same, and the often tragicconsequences of blood transfusions were not understood. As our understanding of theABO group grew, not only did the world of blood transfusion become a great dealsafer, but scientists could now study one of the first human characteristics provento be inherited. A person's ABO blood type was used by lawyers in paternity suits,by police in forensic science, and by anthropologists in the study of differentpopulations.
However, despite their obvious clinical importance, the physiological functions ofABO blood group antigens remain a mystery. People with the common blood type Oexpress neither the A nor B antigen, and they are perfectly healthy. Numerousassociations have been made between particular ABO phenotypes and an increasedsusceptibility to disease. For example, the ABO phenotype has been linked withstomach ulcers (more common in group O individuals) and gastric cancer (more commonin group A individuals). Another observation is that individuals with blood type Otend to have lower levels of the von Willebrand Factor (vWF), which is a proteininvolved in blood clotting.
In 1910, scientists proved that the RBCs antigens were inherited, and that the Aand B antigens were inherited codominantly over O. There was initially someconfusion over how a person's blood type was determined, but the puzzle wassolved in 1924 by Bernstein's "three allele model".
The four basic ABO phenotypes are O, A, B, and AB. After it was found that bloodgroup A RBCs reacted differently to a particular antibody (later calledanti-A1), the blood group was divided into two phenotypes, A1 andA2. RBCs with the A1 phenotype react with anti-A1 andmake up about 80% of blood type A. RBCs with the A2 phenotype do notreact with anti-A1 and they make up about 20% of blood type A. A1 redcells express about 5 times more A antigen than A2 red cells, butboth types of red cell react with anti-A, and as far as transfusion purposes areconcerned, the A1 and A2 blood groups are interchangeable.
The immune system forms antibodies against whichever ABO blood group antigens arenot found on the individual's RBCs. Thus, a group Aindividual will have anti-B antibodies and a group B individual will have anti-Aantibodies. Blood group O is common, and individuals with this blood type willhave both anti-A and anti-B in their serum. Blood group AB is the least common,and these individuals will have neither anti-A nor anti-B in their serum.
The O allele encodes an enzyme with no function, and therefore neither A or Bantigen is produced, leaving the underlying precursor (the H antigen) unchanged.These antigens are incorporated into one of four types of oligosaccharide chain,type 2 being the most common in the antigen-carrying molecules in RBC membranes.Some of the other enzymes involved in the earlier stages of ABO antigensynthesis are also involved in producing antigens of the Hh blood group and theLewis blood group.
A number of illnesses may alter a person's ABO phenotype. Patients can "acquire"the B antigen during a necrotizing infection during which bacteria release anenzyme into the circulation that converts the A1 antigen into a B-like antigen(3). During this time,patients should not receive blood products that contain the B antigen becausetheir sera will still contain anti-B. Once the underlying infection is treated,the patients' blood groups return to normal.
No diseases are known to result from the lack of expression of ABO blood groupantigens, but the susceptibility to a number of diseases has been linked with aperson's ABO phenotype. Such correlations remain controversial and include theobservation that gastric cancer appears to be more common in group A individuals(4), whereas gastric andduodenal ulcers occur more often in group O individuals (5).
A clear correlation has been established between the ABO phenotype and the levelof two proteins involved in blood clotting; factor VII (FVIII) and vonWillebrand factor (vWF) (6).Blood group O individuals have about 25% less FVIII and vWF in their plasma. Itis well established that low levels of FVIII and vWF are a cause of excessbleeding, and therefore it may also be the case that increased levels makeclotting more likely, increasing the risk of both arterial (ischemic heartdisease) and venous (thromboembolic disease) problems. Indeed, non-group Oindividuals have been shown to be at an increased risk of both arterial andvenous disease (6).
HDN caused by ABO antibodies occurs almost exclusively in infants of blood groupA or B who are born to group O mothers (10). This is because the anti-A and anti-B formedin group O individuals tend to be of the IgG type (and therefore can cross theplacenta), whereas the anti-A and anti-B found in the serum of group B and Aindividuals, respectively, tends to be of the IgM type. Although uncommon, casesof HDN have been reported in infants born to mothers with blood group A2 (11) and blood group B (12).
Individuals who are homozygous for null alleles at this locus (h/h) do notproduce H antigen, and because the H antigen is an essential precursor tothe ABO blood group antigens, they cannot produce A and B antigens.Therefore, their serum contains anti-A and anti-B, in addition to potentanti-H. This rare phenotype of H-deficient RBCs is called the "Bombayphenotype" (Oh) after the city in which it was first discovered.Individuals with the Bombay phenotype are healthy, but if they ever needed ablood transfusion, the antibodies in their serum would place them at a highrisk of having an acute hemolytic transfusion reaction. This can be avoidedby using only blood products from a donor who also has the Bombay phenotype(usually a relative).
Distinct molecules called agglutinogens (a type of antigen) are attached to the surface of red bloodcells. There are two different types of agglutinogens, type "A" and type "B". Each type has differentproperties. The ABO blood type classification system uses the presence or absence of these molecules tocategorize blood into four types.
Another level of specificity is added to blood type by examining the presence or absence of the Rh protein.Each blood type is either positive "+" (has the Rh protein) or negative "-" (no Rh protein). For example, aperson whose blood type is "A positive" (A +), has both type A and Rh proteins on the surface of their red bloodcells.
When conducting a blood transfusion, it is important to carefully match the donor and recipient bloodtypes. If the donor blood cells have surface molecules that are different from those of the recipient,antibodies in the recipient's blood recognize the donor blood as foreign. This triggers an immuneresponse resulting in blood clotting. If the donor blood cells have surface molecules that are thesame as those of the recipient, the recipient's body will not see them as foreign and will not mountan immune response.
There are two special blood types when it comes to blood transfusions. People with type Oblood are universal donors because there are no molecules on the surface of the red blood cellsthat can trigger an immune response. People with type AB blood are universal recipients becausethey do not have any antibodies that will recognize type A or B surface molecules.
The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes.[1] For human blood transfusions, it is the most important of the 43 different blood type (or group) classification systems currently recognized by the International Society of Blood Transfusions (ISBT) as of June 2021.[2][3] A mismatch (very rare in modern medicine) in this, or any other serotype, can cause a potentially fatal adverse reaction after a transfusion, or an unwanted immune response to an organ transplant.[4] The associated anti-A and anti-B antibodies are usually IgM antibodies, produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses.
The ABO blood types were discovered by Karl Landsteiner in 1901; he received the Nobel Prize in Physiology or Medicine in 1930 for this discovery.[5] ABO blood types are also present in other primates such as apes and Old World monkeys.[6]
The ABO blood types were first discovered by an Austrian physician, Karl Landsteiner, working at the Pathological-Anatomical Institute of the University of Vienna (now Medical University of Vienna). In 1900, he found that red blood cells would clump together (agglutinate) when mixed in test tubes with sera from different persons, and that some human blood also agglutinated with animal blood.[7] He wrote a two-sentence footnote:
[It] may be said that there exist at least two different types of agglutinins, one in A, another one in B, and both together in C. The red blood cells are inert to the agglutinins which are present in the same serum.[9]
In 1910, Ludwik Hirszfeld and Emil Freiherr von Dungern introduced the term O (null) for the group Landsteiner designated as C, and AB for the type discovered by Sturli and von Decastello. They were also the first to explain the genetic inheritance of the blood groups.[13][14]
Czech serologist Jan Janský independently introduced blood type classification in 1907 in a local journal.[15] He used the Roman numerical I, II, III, and IV (corresponding to modern O, A, B, and AB). Unknown to Janský, an American physician William L. Moss devised a slightly different classification using the same numerical;[16] his I, II, III, and IV corresponding to modern AB, A, B, and O.[12]
The IA allele gives type A, IB gives type B, and i gives type O. As both IA and IB are dominant over i, only ii people have type O blood. Individuals with IAIA or IAi have type A blood, and individuals with IBIB or IBi have type B. IAIB people have both phenotypes, because A and B express a special dominance relationship: codominance, which means that type A and B parents can have an AB child. A couple with type A and type B can also have a type O child if they are both heterozygous (IBi and IAi). The cis-AB phenotype has a single enzyme that creates both A and B antigens. The resulting red blood cells do not usually express A or B antigen at the same level that would be expected on common group A1 or B red blood cells, which can help solve the problem of an apparently genetically impossible blood group.[33] 2ff7e9595c
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