Tyson Greg [e-mail]
Genetics Handout Week 9 Fill in the table Blood type Possible genotypes A AA, AO B BB, BO AB AB____ O OO____
Antigen A_____ B_____ A and B None__
Antibodies anti-B anti-A None anti-A and anti-B
1. Multiple alleles are for traits with more than 2 alleles in a population, but there are only 2 in each individual. 2. Blood types A and B are codominant, and are dominant compared to blood type O. 3. Why do they no longer call blood type O the universal donor and AB the universal acceptor? Because there are many other antigens on blood cells besides A and B, so some of these other antigens may be attacked by antibodies in the person who received blood. 4. Why do people naturally make antibodies for A and B antigens if they have blood type O? What happens if they get a blood transfusion from someone with blood type AB? There are bacteria that have antigens similar to those on A and B red blood cells, so these same antibodies produced to attack the bacteria can attack the transfused red blood cells. If you get a blood transfusion from someone with blood type AB, the foreign red blood cells will be attacked, and clumps of red blood cells and antibodies will form, which will kill you. 5. You add an unknown blood sample to one of type O. No blood clumping is observed. You then add a drop of type A blood, which causes clumping to form. What is the blood type of the original unknown sample? (The antibodies in the blood samples have not been removed) The answer is blood type O. Type O blood has anti-A and anti-B antibodies. Since there is no clumping observed when type O blood is added with the unknown blood, that person must not have neither A nor B antigens, and must be blood type O. The anti-A antibodies attack the type A red blood cells when they are added, causing clumping to form. 6. The Rhesus factor determines another an antigen on red blood cells (independent of blood group). Someone with phenotype DD is Rh+, Dd is Rh+, and dd is Rh- . Someone who is DD or Dd has the D antigen. Someone who is dd lacks the D antigen. 7. A woman is Rh- and her husband is Rh+. Will there be problems with the first Rh+ child? The second? How about a mother who is Rh+, with a child who is Rh-? There will not be a problem with the first child. However, during childbirth, some of the childs blood becomes exposed to the mother. This means that she will be sensitized the to D antigen, and any future Rh+ child will be attacked by the mothers antibodies against the antigen and will die in the womb. This is because these small IgG molecules can cross the placental barrier. A mother who is Rh+ who has an Rh- child will not have a problem no matter how many Rh- children she has. This is because the mother has the D antigen, and the child does not. None of the mothers antibodies will attack the fetus.
Greg Tyson [e-mail]
8. The antibodies that attack the A and B antigens on red blood cells are called IgM. These cannot cross the placental barrier because they are too big. 9. Peters mom is blood type A+ and his dad is B+. He wants to know what his possible blood types are. What do you tell him? His mom could be AO or AA, and his dad could be BB or BO. If both his parents are heterozygous, he could have any blood type: A, B, AB, or O. Additionally, his parents could be DD or Dd for the Rhesus factor. This means if they are both heterozygous, he could be + or -. As a result, he could have any blood type. (You can draw the Punnett squares). 10. On the TV show Maury Francine claims that Bob is the father of her baby. Francine is blood type A and Bob is blood type AB. The baby is blood type O. Bob is going to leave her because he thinks shes been cheating on him. What do you tell them? The baby has the Bombay phenotype. The baby must have an hh genotype, so that whatever the babys blood type genotype, she has type O blood. This is because this is a case of recessive epistasis, where the genotype at one locus masks expression of alleles at a different locus. (Dont worry much about term epistasis; you will learn more about it next week). The hh genotype causes her to show type O blood, independent of her true genotype. 11. Someone with the Bombay Phenotype is lacking the H substance. A normal person with HH or Hh genotype at this locus has the H substance, and can modify the glycosphingolipid to form the A and B antigens. Without this modification dependent on the presence of an H allele, the A and B antigens cannot be made. 12. From what blood types can someone with the Bombay Phenotype receive a transfusion? Trick question: they can only receive blood from other people with the Bombay phenotype. This is because the H antigen that is created in normal peoples blood stimulates an immune reaction in people with the Bombay phenotype.