Q.6 Read the following structure which is a combination of:
Clinical Syndrome : Karyotype : Chromosome Formula : Estimated Frequency at Birth
- (A) Down Syndrome : 47, +13 : 2n+1 : 1/20,000
- (B) Patau Syndrome : 47, +21 : 2n+1 : 1/2,000
- (C) Edward Syndrome : 47, +18 : 2n+1 : 1/8000
- (D) Klinefelter Syndrome : 47, XXY : 2n+1 : 1/500 male births
Choose the correct answer for the above statements from the options given below:
Introduction
Chromosomal disorders arise due to abnormalities in chromosome number caused by meiotic non-disjunction.
The most common condition is aneuploidy where the chromosome number becomes
2n ± 1. Trisomy indicates the presence of one extra chromosome, represented as
2n + 1 (47 chromosomes).
Let us analyse each clinical syndrome with its correct karyotype, chromosome formula and birth frequency.
(A) Down Syndrome
Correct Facts:
- Karyotype: 47, +21
- Chromosome formula: 2n + 1
- Frequency: 1/700–800 births
Down syndrome is caused by Trisomy 21. The question incorrectly mentions
+13, which belongs to Patau syndrome.
Conclusion: ❌ Incorrect
(B) Patau Syndrome
Correct Facts:
- Karyotype: 47, +13
- Chromosome formula: 2n + 1
- Frequency: 1/10,000–20,000 births
Patau syndrome results from Trisomy 13. The question incorrectly shows +21.
Conclusion: ❌ Incorrect
(C) Edward Syndrome
Correct Facts:
- Karyotype: 47, +18
- Chromosome formula: 2n + 1
- Frequency: 1/8000 births
Edward syndrome is due to Trisomy 18. All details in the statement match correctly.
Conclusion: ✅ Correct
(D) Klinefelter Syndrome
Correct Facts:
- Karyotype: 47, XXY
- Chromosome formula: 2n + 1
- Frequency: 1/500 male births
This is a sex chromosome aneuploidy where males possess an extra X chromosome (XXY).
The information given is accurate.
Conclusion: ✅ Correct
Quick Revision Table
| Syndrome | Karyotype | Formula | Frequency | Status |
|---|---|---|---|---|
| Down | 47, +21 | 2n + 1 | 1/700–800 | Incorrect |
| Patau | 47, +13 | 2n + 1 | 1/10,000–20,000 | Incorrect |
| Edward | 47, +18 | 2n + 1 | 1/8000 | Correct |
| Klinefelter | 47, XXY | 2n + 1 | 1/500 males | Correct |
Final Answer
(C) and (D) only
