Question

The genotype of a husband and wife are $I^A I^B$ and $I^A I^O$. Among the blood types of their children, how many different genotypes and phenotypes are possible?

• A. 3 genotypes; 3 phenotypes
• B. 4 genotypes; 3 phenotypes
• C. 4 phenotypes; 3 genotypes
• D. 4 phenotypes; 4 genotypes

Hint:

When counting phenotypes, remember that heterozygous ($I^A I^O$) and homozygous ($I^A I^A$) results look identical in a blood test. They both count as "Phenotype A."

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Human blood groups are determined by three alleles: $I^A$, $I^B$, and $I^O$. $I^A$ and $I^B$ are co-dominant, while $I^O$ is recessive to both. Genotype refers to the genetic makeup, while phenotype refers to the expressed blood group (A, B, AB, or O).
Step 2: Detailed Explanation:
1. Perform a cross between $I^A I^B$ and $I^A I^O$:
- $I^A \times I^A \to I^A I^A$ (Genotype 1, Phenotype: A)
- $I^A \times I^O \to I^A I^O$ (Genotype 2, Phenotype: A)
- $I^B \times I^A \to I^A I^B$ (Genotype 3, Phenotype: AB)
- $I^B \times I^O \to I^B I^O$ (Genotype 4, Phenotype: B)
2. Counting Genotypes: There are 4 distinct combinations ($I^A I^A, I^A I^O, I^A I^B, I^B I^O$).
3. Counting Phenotypes:
- $I^A I^A$ and $I^A I^O$ both result in Blood Group A.
- $I^A I^B$ results in Blood Group AB.
- $I^B I^O$ results in Blood Group B.
- Total phenotypes = 3 (A, AB, and B).
Step 3: Final Answer
There are 4 different genotypes and 3 different phenotypes possible.