BIOL 221 Lecture Notes - Lecture 1: Hemolytic Disease Of The Newborn, Fetal Circulation, Rh Blood Group System

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10 Feb 2020

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Erythroblastosis fetalis is a hemolytic disorder in which antibodies against the rh factor cross the placenta from an rh negative female into the blood of the rh positive child. (what must the father"s rh have been to have produced an rh positive child?) In order for this to happen, the mother must have been exposed to rh positive blood. Maternal and fetal blood doesn"t normally mix, but when placental blood vessels rupture during birth, the mother may be exposed. Previous miscarriages or abortions and previous blood transfusions are also possible routes of exposure. The drug rhogam has been used successfully to suppress rh negative mothers" immune responses to rh positive blood. For additional practice, complete this table of blood types. I, indicate all the blood types of the recipients to whom the indicated type of blood may be given. (for example, ab+ blood may only be given to ab+ recipients. )

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As we discussed in âlectureâ, Rh is the most complex of the blood group types, involving at least 45 different antigens. The most clinically important antigen, D or RhO, is encoded by the gene RhD which is found on chromosome 1. Individuals that are Rh-positive have either one or two RhD genes, whereas the Rh-negative phenotype is caused by the absence of the RhD gene. (The antithetical allele d does not exist, however the letter "d" is used to indicate the D-negative phenotype). For the purpose of this homework, we will simplify things. Assume that the Rh blood group has only two alleles: the Rh-positive allele (D) and the Rh-negative allele (d). Erythroblastosis fetalis (EF) is a condition that causes the mother's red blood cells to attack those of the baby as if they were any foreign invaders. It is referred to as hemolytic anemia of the newborn. It is caused by anti-Rh antibodies from the mother which pass through the placenta and attack fetal blood cells that happen to be Rh-positive. Babies that are at risk for this condition are those with Rh-positive blood, whose mothers are Rh-negative (dd).

Consider a population under Hardy-Weinberg equilibrium, where the frequency of the Rh-negative allele, d, is 0.3. What is the frequency of crosses that could potentially produce children with erythroblastosis fetalis?

tealplatypus721

As we discussed in âlectureâ, Rh is the most complex of theblood group types, involving at least 45 different antigens. Themost clinically important antigen, D orRh_O, is encoded by the gene RhD whichis found on chromosome 1. Individuals that are Rh-positive haveeither one or two RhD genes, whereas the Rh-negativephenotype is caused by the absence of the RhD gene. (Theantithetical allele d does not exist, however the letter"d" is used to indicate the D-negative phenotype). For the purposeof this homework, we will simplify things. Assume that the Rh bloodgroup has only two alleles: the Rh-positive allele (D) andthe Rh-negative allele (d).

Erythroblastosis fetalis (EF) is a condition that causes themother's red blood cells to attack those of the baby as if theywere any foreign invaders. It is referred to as hemolytic anemia ofthe newborn. It is caused by anti-Rh antibodies from the motherwhich pass through the placenta and attack fetal blood cells thathappen to be Rh-positive. Babies that are at risk for thiscondition are those with Rh-positive blood, whose mothers areRh-negative (dd).

Side note: Hereâs a current headline thataddresses this condition. Itâs well worth a read!

http://www.cnn.com/2015/06/09/health/james-harrison-golden-arm-blood-rhesus/index.html

Consider a population under Hardy-Weinberg equilibrium, where thefrequency of the Rh-negative allele, d, is 0.3. What isthe frequency of crosses that could potentially produce childrenwith erythroblastosis fetalis?

blushporpoise137

The A antigen (the protein that makes A blood A blood) is embedded in the red blood cell (RBC) membrane. Blood group A individuals will automatically carry antibodies (proteins that are in the blood plasma-liquid part of blood) that will attack blood group B cells. Blood group B individuals will carry antibodies that will attack blood group A cells. Blood group O individuals, lacking either of the A or B antigens will carry BOTH types of antibodies and will attack either A or B cells. When there is a transfusion with incompatible blood groups, cells can clump creating blockages in arteries throughout the body. Other pathways can lead to the lysing of RBCâs which will release their contents into the bloodstream elevating these component in the blood which can have sever effects on the heart (potassium primarily-in case you are interested).

Remember, the Rh is a typical one gene, two allele scenario. Rh+ blood can accept Rh+ or Rh- blood. A person with Rh- blood can only receive Rh- blood. Unlike ABO where an individual manufactures the antibody to an antigen they lack without prior exposure, the Rh factor requires previous exposure to illicit an immune response. If a Rh- person is exposed to Rh+ blood, the individual will create the antibody against the Rh antigen. Now, if Rh+ blood is introduced into this individual again, the recipientâs blood contains anti-Rh antibodies and will attack the Rh+ cells-Bad news for the recipient. This is the same thing that happens with an Rh- mom who gets pregnant with an Rh+ baby. By the time the first Rh+ baby is born and blood mixing may have occurred during late pregnancy (small breaks in the placenta can cause some of babyâs blood to mix with that of mom), first baby escapes unharmed. Subsequent babies arenât so lucky.

If there are small tears in the placenta (which are normal), momâs anti Rh antibodies can go in and attack the Rh+ babyâs blood. This can kill the baby. Now, Rh- moms are given a substance that will coat the babyâs RBCâ; kind of like putting them into stealth mode so they canât be seen by momâs immune system. Later-poof, out pops unaffected baby.

1. What blood type(s) can be given to an A positive individual?

2. If you have B negative blood, what blood types can you receive?

3. What blood types can an O negative receive? O positive?

4. If a man is blood group B and his wife is blood group A what blood type(s) are you 100% sure they could produce in their children?

5. If you have a blood group O father and a blood group B mother, can they produce an O child? Explain your answer.

6. You have a male friend who is blood group AB. He is successful in business but knows very little about biology. His wife just had an O child. Knowing that you have been studying the genetics of blood groups, he asks you for an education on blood groups. What do you think about this situation?

7. A woman is AB and her husband is A. They have a B child. What are all the blood groups possible in their children if he is heterozygous?

8. A woman is Rh- and her husband is Rh+. Their first baby is Rh-. What is the genotype, with respect to Rh, of the parents? What is the probability their next child will be Rh+? Does the woman have to worry about any issues with future children? Explain!

BIOL 221 Lecture Notes - Lecture 1: Hemolytic Disease Of The Newborn, Fetal Circulation, Rh Blood Group System

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