A man woman are both affected by vitamin D resistance rickets, which is a dominant sex-linked allele. All of the female of springs of this couple are affected with rickets but some of the male offsprings are not. What are the genotypes of the parents ?

Options

A. Both are homozygous for the trait.
B. Two woman has two dominant alleles and man han one dominant allele.
C. Both parents have only recessive alleles.
D. Each parent has only one dominant allele.

Answer

To determine the genotypes of the parents affected by vitamin D resistant rickets, we need to analyze the information given in the question step by step.

### Step 1: Understand the inheritance pattern
Vitamin D resistant rickets is described as a dominant sex-linked trait. This means that the gene responsible for this condition is located on the X chromosome, and only one copy of the dominant allele is needed for an individual to express the trait.

### Step 2: Define the alleles
Let's denote the dominant allele for vitamin D resistant rickets as "T" and the normal allele as "t". Since it is a sex-linked trait, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).

### Step 3: Analyze the parents' conditions
Both parents are affected by the condition, which means they must have at least one copy of the dominant allele "T".

- The male parent can have the following genotype:
- X^T Y (where X^T represents the X chromosome with the dominant allele)

- The female parent must have at least one dominant allele as well. Since all female offspring are affected, the female parent must have the genotype:
- X^T X^t (heterozygous, one affected X and one normal X)

### Step 4: Analyze the offspring
According to the question, all female offspring are affected, which is consistent with the female parent being X^T X^t.

For male offspring, since some are affected and some are not, we can deduce the following:
- Males inherit their X chromosome from their mother and their Y chromosome from their father. Therefore, if a male offspring is affected, he must inherit the X^T from his mother. If he is unaffected, he must inherit the normal X^t from his mother.

### Step 5: Conclusion of genotypes
Thus, the genotypes of the parents are:
- Male parent: X^T Y
- Female parent: X^T X^t

### Final Answer:
- Male Parent Genotype: X^T Y
- Female Parent Genotype: X^T X^t

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