A woman who is homozygous for Incontinentia pigmenti is married to a normal man. In their children, IP appears in

Options

A. only sons
B. 50% of chilren
C. Only daughters
D. All the children

Answer

To solve the question regarding the inheritance of Incontinentia pigmenti (IP) in children of a homozygous woman and a normal man, we can follow these steps:

### Step 1: Understand the Genetic Basis of Incontinentia Pigmenti
Incontinentia pigmenti is an X-linked dominant disorder. This means that the gene responsible for the disorder is located on the X chromosome, and only one copy of the mutated gene is sufficient to express the trait.

**Hint:** Remember that X-linked traits are passed down through the X chromosome, and the inheritance pattern differs between males and females.

### Step 2: Determine the Genotype of the Parents
The woman is homozygous for Incontinentia pigmenti, which means her genotype is XX^IP (where X^IP represents the X chromosome carrying the IP allele). The normal man has a normal X chromosome and a Y chromosome, so his genotype is XY.

**Hint:** Identify the genotypes of both parents clearly to understand how the trait will be passed on.

### Step 3: Predict the Genotypes of the Children
When these two parents have children, the mother will pass on one of her X chromosomes (X^IP), while the father will pass on either his X or Y chromosome. This results in the following possible combinations for their children:
- Daughters: X^IP from the mother and X from the father (X^IPX)
- Sons: X^IP from the mother and Y from the father (X^IPY)

**Hint:** Consider the combinations of X and Y chromosomes from both parents to determine the potential genotypes of the offspring.

### Step 4: Analyze the Offspring's Traits
Since all daughters will have the genotype X^IPX, they will express the trait of Incontinentia pigmenti. All sons will have the genotype X^IPY, and they will also express the trait. Therefore, all children, regardless of sex, will exhibit the trait.

**Hint:** Check how the trait manifests in both male and female offspring based on their genotypes.

### Step 5: Conclusion
Based on the analysis, the trait of Incontinentia pigmenti will appear in all children of the couple. Therefore, the correct answer is that IP appears in all the children.

**Hint:** Summarize your findings clearly to arrive at the final answer.

### Final Answer:
Incontinentia pigmenti appears in all the children (Option D).

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