Question

What is transition and transversion mutations respectively means?

• A. Purine is replaced by pyrimidine in transition and purine is replaced by purine in transversion
• B. Purine is replaced by purine in transition and purine is replaced by pyrimidine in transversion
• C. Purine is replaced by purine in transition and transversion
• D. Pyrimidine is replaced by pyrimidine in transition and in transversion

Hint:

• Transition Purine \(\leftrightarrow\) Purine (A \(\leftrightarrow\) G); Pyrimidine \(\leftrightarrow\) Pyrimidine (C \(\leftrightarrow\) T). (Same type of base).
• Transversion Purine \(\leftrightarrow\) Pyrimidine (A/G \(\leftrightarrow\) C/T). (Different type of base).
• Remember: PuR}ines are A}, G} (Pure As Gold). Pyrimidines are C}, T}, U} (CUT the Py).

Answer 1

The Correct Option is B

Point mutations are changes in a single nucleotide base in DNA. They are classified based on the type of base substitution:

• Transition: A type of point mutation where a purine nucleotide is replaced by another purine nucleotide (A \(\leftrightarrow\) G), OR a pyrimidine nucleotide is replaced by another pyrimidine nucleotide (C \(\leftrightarrow\) T in DNA, or C \(\leftrightarrow\) U in RNA). The type of base (purine or pyrimidine) remains the same.
• Transversion: A type of point mutation where a purine nucleotide is replaced by a pyrimidine nucleotide, OR a pyrimidine nucleotide is replaced by a purine nucleotide. The type of base changes. (Purine \(\leftrightarrow\) Pyrimidine; e.g., A \(\leftrightarrow\) C, A \(\leftrightarrow\) T, G \(\leftrightarrow\) C, G \(\leftrightarrow\) T).

Purines are Adenine (A) and Guanine (G). Pyrimidines are Cytosine (C) and Thymine (T) (Uracil (U) in RNA). Let's analyze the options (interpreting "X is replaced by Y in transition" as one example of transition): (a) "Purine is replaced by pyrimidine in transition..." - Incorrect. This is transversion. "...and purine is replaced by purine in transversion" - Incorrect. This is transition. (b) "Purine is replaced by purine in transition..." - Correct (this is one type of transition, A\(\leftrightarrow\)G). "...and purine is replaced by pyrimidine in transversion" - Correct (this is one type of transversion, e.g., A\(\rightarrow\)C or A\(\rightarrow\)T). This option captures one example of each correctly. (c) "Purine is replaced by purine in transition and transversion": Incorrect for transversion. (d) "Pyrimidine is replaced by pyrimidine in transition and in transversion": Incorrect for transversion. (Pyrimidine replaced by pyrimidine is a transition). Option (b) provides correct examples for each: Transition: Purine \(\leftrightarrow\) Purine (e.g., A to G) OR Pyrimidine \(\leftrightarrow\) Pyrimidine (e.g., C to T). Option says "Purine is replaced by purine". Transversion: Purine \(\leftrightarrow\) Pyrimidine (e.g., A to C). Option says "purine is replaced by pyrimidine". This option best describes the two types based on the examples given. \[ \boxed{\text{Purine is replaced by purine in transition and purine is replaced by pyrimidine in transversion}} \]