Which of the following should be avoided in biological marriage?

Options

A. `A^(+)` boy and `A^(+)` girl
B. `A^(+)` boy and `A^(-)` girl
C. `O^(+)` boy and `O^(+)` girl
D. `O^(-)` boy and `O^(+)` girl

Explanation

**Step-by-Step Solution:**

1. **Understanding Biological Marriage**: Biological marriage refers to the union between individuals of different Rh blood types, specifically an Rh positive male and an Rh negative female.

2. **Rh Factor Basics**: The Rh factor is a protein that can be present on the surface of red blood cells. If a person has this protein, they are Rh positive (Rh+); if they do not, they are Rh negative (Rh-). The Rh positive trait is dominant over the Rh negative trait.

3. **First Pregnancy Scenario**: In a marriage where the father is Rh positive and the mother is Rh negative, the first child conceived could be Rh positive. The Rh negative mother does not have the Rh antigen but has antibodies against it.

4. **Immune Response**: During the first pregnancy, the mother's immune system does not react against the Rh positive fetus because she has not yet been exposed to the Rh antigen. However, her body will start producing antibodies against the Rh factor.

5. **Second Pregnancy Scenario**: If the mother becomes pregnant again with another Rh positive child, her body already has antibodies from the first pregnancy. These antibodies can cross the placenta and attack the Rh positive blood cells of the fetus.

6. **Consequences of Antibody Attack**: The attack by the mother's antibodies can lead to severe complications for the fetus, such as hemolytic disease of the newborn, which can cause jaundice, anemia, or even fetal death. This condition is known as erythroblastosis fetalis.

7. **Conclusion**: Due to the risk of these severe complications, a biological marriage between an Rh positive father and an Rh negative mother should be avoided.

**Final Answer**: The biological marriage that should be avoided is between an Rh positive male and an Rh negative female.

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