Using your knowledge of ABO blood group inheritance, is it genetically possible for parents with blood group O and AB to have a child with blood group B? Show the possible genotypes.

• Mr. Conteh has blood group O, so his genotype must be $I^O I^O$.
• Mrs. Conteh has blood group AB, so her genotype must be $I^A I^B$.

Mr. Conteh can only pass on the $I^O$ allele.
Mrs. Conteh can pass on either the $I^A$ allele or the $I^B$ allele.

Possible offspring genotypes:

• If Mrs. Conteh passes $I^A$: $I^A I^O$ (Blood group A)
• If Mrs. Conteh passes $I^B$: $I^B I^O$ (Blood group B)

The possible genotypes for their children are $I^A I^O$ and $I^B I^O$.
The possible phenotypes are Blood Group A and Blood Group B.

Therefore, having a child with blood group B ($I^B I^O$) is possible.

b) If not, which parent's genotype is inconsistent with the child's blood type?

Since it is possible for them to have a child with blood group B, neither parent's genotype is inconsistent with the child's blood type.

c) Briefly explain to the parents how blood group inheritance works to clarify their misunderstanding.

Blood group inheritance involves alleles from both parents. You each contribute one allele to your child. Mr. Conteh, with blood group O, has two $I^O$ alleles. Mrs. Conteh, with blood group AB, has one $I^A$ allele and one $I^B$ allele. When they combine, Mr. Conteh always passes an $I^O$ allele. Mrs. Conteh can pass either her $I^A$ or her $I^B$ allele. If she passes her $I^B$ allele, the child's genotype will be $I^B I^O$, which results in blood group B because the $I^B$ allele is dominant over the $I^O$ allele. This means the child is biologically yours.

Q6: Mariama and Ibrahim

a) Explain how Rh factor inheritance could cause complications in this couple's pregnancy.

Rh factor inheritance can cause complications if an Rh-negative mother (Mariama) carries an Rh-positive fetus. The Rh factor is determined by a dominant allele (Rh+) and a recessive allele (Rh-). Mariama is Rh- (genotype $rr$). Ibrahim is Rh+ (genotype $RR$ or $Rr$). If Ibrahim is heterozygous ($Rr$), there is a chance their child could inherit the dominant Rh+ allele from him and be Rh-positive. During childbirth, fetal Rh+ blood cells can enter the mother's Rh-negative bloodstream, causing her immune system to produce anti-Rh antibodies. These antibodies can then attack the red blood cells of a subsequent Rh-positive fetus, leading to hemolytic disease of the newborn (HDN).

b) Why was the first baby unaffected but the second one at risk?

The first baby was likely unaffected because the mother's immune system typically gets exposed to the Rh+ blood of the fetus during the delivery of the first baby. This initial exposure sensitizes the mother, causing her to produce anti-Rh antibodies. However, these antibodies are usually produced too slowly or in insufficient quantities to harm the first baby significantly. For the second pregnancy, if the fetus is also Rh-positive, the mother's pre-existing anti-Rh antibodies, which were formed after the first pregnancy, can cross the placenta and attack the red blood cells of the second fetus, putting it at risk of HDN.

c) What preventive measure should be taken in future pregnancies, and when?

The preventive measure is the administration of RhoGAM (Rh immune globulin). This injection contains anti-Rh antibodies that destroy any fetal Rh+ red blood cells in the mother's circulation before her immune system can become sensitized and produce its own antibodies. It should be taken during pregnancy, typically around 28 weeks of gestation, and again within 72 hours after birth if the baby is found to be Rh-positive. It is also given after any event that could cause fetal-maternal blood mixing, such as miscarriage, abortion, or amniocentesis.