sickle cell anemia fact sheetBiology: checking my answers to questions?

**These are questions on practice sheet for my upcoming test. Questions not graded, just for practice**

Question 1:

ABO blood-type in humans is determined by 3 alleles for the I gene (I^A, I^B and i) where i is recessive and I^A and I^B are codominant. In a case of disputed paternity, a mother is type O blood and the child is type B blood. One possible father has type AB blood and one has type A blood. Which is the father? [My answer: type AB] What is the genotype of the father? [my answer: I^A I^B] What is the genotype of the mother? [not sure] What is the genotype of the child? [not sure]


Question 2:
The inheritance of sickle cell anemia is governed by incomplete dominance. The Hb gene codes for hemoglobin in red blood cells. There are two alleles for this gene: Hb^A which codes for normal hemoglobin and Hb^S which codes for sickle cell hemoglobin. A woman with normal hemoglobin marries a man with sickle cell trait. Their children have ____% chance of having a normal hemoglobin, a ___% chance of having sickle cell trait and a __% chance of having sickle cell anemia. (the fact that there was two answers for sickle cell threw me off)

Question 3:
Hemophilia is determined by a recessive allele for the H gene on the X chromosome. A man with hemophilia marries a woman who does not have hemophilia and is not a carrier. What is the genotype of the man? [ i put: Hh]sickle cell anemia fact sheet Genotype of the woman?: [ i put: HH ?] They have a __% chance of having a son without hemophilia. They have a ___% chance of having a son with hemophilia. They have a ___% chance of having a daughter with hemophilia and a __% chance of having a daughter who is a carrier.

Really getting confused...can someone help me?
Question 1: You're correct for the first two. To answer the next two, remember that the recessive allele will be i, not I^A or I^B. I^A codes for antigen A to be produced in blood cells, and I^B codes for antigen B to produce antigen B in blood cells. i doesn't code for any antigen. When someone's blood type is O, neither type of antigen is present. Therefore, the mother's genotype is ii.

The mother can only pass on an i to her child. The father can pass on I^A or I^B. If he passed on I^A, the child's genotype would be I^A i, so the blood type would be A. If he passed on I^B, the genotype of the child would be I^B i, and the blood type would be B. You already know that the child has type B blood, so the genotype must be I^B i.


Question 2: The difference between sickle cell trait and sickle cell anemia is the severity of the disease. If you have sickle cell anemia, your genotype is Hb^S Hb^S. ALL of your blood cells look like sickles. If you have sickle cell trait, your genotype is Hb^A Hb^S, and only some of your blood cells look like sicklesickle cell anemia fact sheets. The rest of your blood cells look normal and function as usual. Since the woman has normal hemoglobin, her genotype is Hb^A Hb^A. The man has sickle cell trait, so his genotype is Hb^A Hb^S.

For the kids to have normal hemoglobin, they must have Hb^A Hb^A. The woman can only pass on Hb^A, so the chance of them getting that one allele is 100%. The man can pass on Hb^A OR Hb^S, so there's a 1 in 2 chance, or 50% chance, that the kids will inherit the Hb^A allele. Multiply those two chances together to get the chance of having normal hemoglobin: 1 * .5 = .5 = 50%. I'll let you work out the other two on your own.


Question 3: We write sex-linked traits like this: X^H X^h (for a woman who is a carrier of the hemophilia trait) or X^H Y (for a man who does not have hemophilia and is not a carrier). Remember that human females are XX and males are XY. The trait is on the X chromosome, so males cannot be carriers of this disease - they either have the recessive allele or they don't. Females, on the other hand, could carry the trait without expressing it, because the allele on the other X chromosome would make up for it. Once you've figured out the genotypes of the parents, you can go through the same process that we did for Question 2 to figure out the chances of having kids with these traits.