Before You Begin
Question #45831
The Question
A hemophilic man marries a homozygous normal woman. They have a child diagnosed with Turner's syndrome (45, XO). Clinical tests reveal that the child has normal blood clotting. Which of the following statements correctly explains the meiotic error and the genetic basis of this phenotype?
Options
- A.
Non-disjunction during maternal meiosis produced an 'O' ovum, which was fertilized by an X-bearing sperm from the father.
- B.
Non-disjunction during paternal meiosis produced a nullo-sex sperm, which fertilized a normal X-bearing ovum from the mother.
- C.
The child inherited the X^h chromosome from the father, but the recessive hemophilia allele is not expressed due to the absence of a second X chromosome.
- D.
The child inherited the X^h chromosome from the father, but the trait is masked by X-chromosome inactivation (dosage compensation).
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Hemophilia|Turner Syndrome|X-linked Genes
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often rigidly apply the Mendelian rule that a daughter must inherit an X chromosome from her father.
In aneuploidy (Turner's syndrome), the single X chromosome can be exclusively maternal.
The trap tests the ability to deduce the source of the meiotic error (paternal non-disjunction) based on the absence of the father's X-linked phenotype.
It also addresses the misconception that a single recessive allele in a female is always masked, failing to recognize pseudo-dominance in XO individuals.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Sex-Linked Recessive Inheritance |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |