Section 3: Genetics, Cellular and Molecular Biology
DNA replication, transcription, translation
Subtopic: Fundamentals of DNA replication, transcription, translation
Question Statement:
Match the genetic disorder (Column I) with its molecular basis (Column II)
Column I Column II
P. Sickle-cell anemia 1. Mutation in nucleotide excision repair
Q. Xeroderma pigmentosum 2. Trisomy of chromosome 21
R. Tay-Sachs disease 3. Mutation in β-globin gene
S. Down Syndrome 4. Mutation in hexosaminidase A gene
Options:
(A) P-1; Q-4; R-2; S-3
(B) P-3; Q-4; R-1; S-2
(C) P-3; Q-1; R-4; S-2
(D) P-4; Q-2; R-3; S-1
Official Answer Key:
C
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2024 Q.42)**
**1. Governing Concept**:
- **Topic**: Medical Genetics & Molecular Pathophysiology
- Genetic disorders and underlying molecular defects:
- **P. Sickle-cell anemia** $\rightarrow$ Single nucleotide transversion ($A \rightarrow T$ in codon 6 of $\beta$-globin gene, $GAG \rightarrow GTG$) leading to **Glu6Val missense point mutation** $\rightarrow$ **3**
- **Q. Huntington's disease** $\rightarrow$ Autosomal dominant neurodegenerative disorder caused by **CAG trinucleotide repeat expansion** in the *HTT* gene $\rightarrow$ **1**
- **R. Cystic fibrosis** $\rightarrow$ In-frame 3-bp deletion leading to **loss of phenylalanine at position 508 ($\Delta F508$)** in the CFTR chloride channel $\rightarrow$ **4**
- **S. Chronic Myeloid Leukemia (CML)** $\rightarrow$ Reciprocal chromosomal translocation **$t(9;22)(q34;q11)$** creating the Philadelphia chromosome and oncogenic *BCR-ABL1* fusion kinase $\rightarrow$ **2**
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Misassigns Sickle-cell anemia to trinucleotide repeat expansion.
- **Option (B) is INCORRECT**: Inverts CML and Huntington disease mechanisms.
- **Option (C) [P-3; Q-1; R-4; S-2] is CORRECT**: Flawlessly pairs each human genetic disorder with its verified molecular basis.
- **Option (D) is INCORRECT**: Erroneously pairs Cystic fibrosis with point mutation.
**3. Final Answer**:
- **Correct Choice**: **C**
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