Case Study:

In a family from Maharashtra, a 10-year-old boy named Aarav was diagnosed with haemophilia, a genetic disorder that affects blood clotting. His parents appeared normal, but further medical investigation revealed that his mother was a carrier of the defective gene. The disorder is known to be X-linked recessive.

A genetic counselor constructed a pedigree chart for three generations. It showed that Aarav’s maternal grandfather also had haemophilia, while his maternal grandmother was normal. Aarav’s sister showed no symptoms but had a 50% probability of being a carrier.

Statistical analysis suggested that if Aarav’s sister marries a normal male, there is a 25% chance that their male child may inherit haemophilia. The family faced an important decision regarding genetic testing and future family planning.

Doctors recommended prenatal diagnosis techniques such as amniocentesis to detect the disorder early in pregnancy. However, ethical concerns and lack of awareness posed challenges in decision-making.

This case demonstrates the inheritance pattern of sex-linked disorders, the importance of pedigree analysis, probability in genetics, and the role of genetic counseling in India’s healthcare system.

Questions:

Section A - MCQs

1. Why is haemophilia more common in males?

A. Males have more chromosomes
B. It is an autosomal disorder
C. Males have only one X chromosome
D. It affects only females

2. Aarav’s mother is a carrier because:

A. She shows symptoms of disease
B. She has one normal and one defective allele
C. She has two defective alleles
D. She lacks X chromosome

3. If a carrier female marries a normal male, the probability of an affected son is:

A. 0%
B. 25%
C. 50%
D. 75%

4. Pedigree analysis is useful to:

A. Cure genetic diseases
B. Identify inheritance patterns
C. Change DNA sequence
D. Increase mutation rate

Section B - Short Answer Questions

1. Explain why females are less affected by X-linked recessive disorders.

2. How does pedigree analysis help in genetic counseling? 

3. Calculate the probability of a carrier female having a normal daughter.

Section C - Long Answer Question

1. Suppose Aarav’s sister undergoes genetic testing and is found to be a carrier.

• Predict the possible genotypes and phenotypes of her children if she marries a normal male.
• Explain the role of prenatal diagnosis in such cases.
• Discuss ethical concerns related to genetic testing in India.

Answer Key:

MCQs:

1. C
2. B
3. B
4. B

Short Answers:

1. Females have two X chromosomes, so a normal allele can mask the defective one. Males have only one X chromosome, so the disorder is expressed if the gene is present.

2. Pedigree analysis helps trace inheritance patterns, identify carriers, and predict risk of genetic disorders, aiding informed decision-making.

3. Carrier female (XᴴXʰ) × normal male (XᴴY)
    Possible daughters:

• XᴴXᴴ (normal)
• XᴴXʰ (carrier)
  Probability of normal daughter = 50%

Long Answer:

Genotypes & Phenotypes:

• Sons: 50% haemophilic, 50% normal
• Daughters: 50% carriers, 50% normal

Prenatal Diagnosis:
Techniques like amniocentesis detect genetic disorders before birth, helping in early decision-making.

Ethical Concerns:

• Misuse for sex selection
• Emotional stress
• Privacy issues