Question

Choose the correct statement(s) with respect to Down's syndrome
i. Down's syndrome results from non-disjunction of \( 21^{st} \) chromosome during gamete formation.
ii. Down's syndrome is a sex chromosomal disorder observed in immature mothers who are below the age of 18 .
iii. These patients have mild mental retardation, poor skeletal development, flat hands, stubby fingers and palms are broader.
iv. The have 44 A with XO type of karyotype.
v. The risk of giving birth to a Down Syndrome child is more in mothers who are over 45 years of age.

• A. ii and iv only
• B. i, iii and v only
• C. i and ii only
• D. only V

Hint:

Down’s syndrome: Trisomy 21 + risk ↑ with maternal age.

Answer 1

The Correct Option is B

Concept:
Down's syndrome is an autosomal aneuploidy caused by trisomy of chromosome 21.

Step 1: Analyze statement i. Non-disjunction of chromosome 21 during meiosis leads to trisomy 21. \checkmark

Step 2: Analyze statement ii. It is not a sex chromosomal disorder and is more common in older mothers, not younger ones. $\times$

Step 3: Analyze statement iii. Typical features include:
• Mild intellectual disability
• Broad palms, stubby fingers
• Poor skeletal development \checkmark

Step 4: Analyze statement iv. XO karyotype corresponds to Turner's syndrome, not Down's syndrome. $\times$

Step 5: Analyze statement v. Risk increases with maternal age, especially above 40–45 years. \checkmark

Step 6: Conclusion. \[ \text{Correct statements = i, iii, v} \]