Question

Which of the following statements are true for DNA: A. DNA specimens isolated from different tissues of the same species have same base composition. B. DNA extracted from similar species have same base composition. C. Adenine residue can be different from thymine residues. D. Guanine residues are always equal to cytosine residues. E. Base composition cannot be used to classify organism.

• A. A, B, D and E only
• B. A, B and D only
• C. A, B, C and E only
• D. A, B, C and D only

Hint:

For double-stranded DNA, remember Chargaff's rule: \(A=T\) and \(G=C\). DNA base composition is useful for comparison and classification.

Answer 1

The Correct Option is B

Concept:
DNA base composition follows Chargaff's rule. According to Chargaff's rule, in double-stranded DNA: \[ A = T \] and \[ G = C \]

Step 1: Check statement A.
DNA isolated from different tissues of the same species has the same base composition because the genome is the same in different tissues. \[ A \text{ is correct} \]

Step 2: Check statement B.
Closely related or similar species may show similarity in base composition. Therefore, this statement is considered correct in the given context. \[ B \text{ is correct} \]

Step 3: Check statement C.
In double-stranded DNA, adenine pairs with thymine. Therefore, the amount of adenine is equal to thymine. \[ A = T \] So adenine residues cannot be different from thymine residues in normal double-stranded DNA. \[ C \text{ is incorrect} \]

Step 4: Check statement D.
Guanine pairs with cytosine. Therefore, guanine residues are equal to cytosine residues. \[ G = C \] \[ D \text{ is correct} \]

Step 5: Check statement E.
Base composition can help in classification and comparison of organisms. Therefore, statement E is incorrect. \[ E \text{ is incorrect} \] Thus, the correct statements are: \[ A,\ B \text{ and } D \] \[ \therefore \text{Correct Answer is (B)} \]