Question

For which one of the following parents, their children will NOT have the same blood group phenotype as either of the parents?

• A. Father: AB; Mother: O
• B. Father: A; Mother: O
• C. Father: AB; Mother: A
• D. Father: O; Mother: B

Hint:

An AB parent can never pass an "AB" combo in a single gamete, and an O parent can only give "i".
So, AB $\times$ O always yields 100% A and B offspring (never AB or O). This classic cross is a favorite in genetic exams!

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This genetics problem involves the ABO blood group system. We need to find the parental combination where 100% of the children will have a blood group phenotype that is completely different from both parents.

Step 2: Key Formula or Approach:
Recall the alleles of the ABO blood group system:
- $I^A$ and $I^B$ are codominant alleles.
- $i$ is the recessive allele.
- Phenotype A: $I^A I^A$ or $I^A i$.
- Phenotype B: $I^B I^B$ or $I^B i$.
- Phenotype AB: $I^A I^B$.
- Phenotype O: $ii$.

Step 3: Detailed Explanation:
Let's analyze each parent combination:

• Option (A): Father: AB ($I^A I^B$) $\times$ Mother: O ($ii$)
- The father produces gametes with either the $I^A$ or $I^B$ allele.
- The mother produces gametes only with the $i$ allele.
- Possible offspring genotypes:
- $I^A i$ (Phenotype: Blood Group A)
- $I^B i$ (Phenotype: Blood Group B)
- Parents' phenotypes are AB and O. Children's phenotypes can only be A or B.
- Therefore, none of the children will share a phenotype with either parent. This matches the condition.

• Option (B): Father: A ($I^A I^A$ or $I^A i$) $\times$ Mother: O ($ii$)
- If the father is heterozygous ($I^A i$), they can have children with genotype $ii$ (Phenotype O, same as mother) or $I^A i$ (Phenotype A, same as father).

• Option (C): Father: AB ($I^A I^B$) $\times$ Mother: A ($I^A I^A$ or $I^A i$)
- They can easily have children with genotype $I^A I^A$ or $I^A i$ (Phenotype A) or $I^A I^B$ (Phenotype AB), which match the parents.

• Option (D): Father: O ($ii$) $\times$ Mother: B ($I^B I^B$ or $I^B i$)
- If the mother is heterozygous ($I^B i$), they can have children with genotype $ii$ (O) or $I^B i$ (B), both of which match the parents' phenotypes.

Step 4: Final Answer:
Only combination (A) guarantees that none of the offspring will have the same blood group phenotype as either parent.