Which one of the following statements is not true regarding gel electrophoresis technique?
Answer: (C) The presence of chromogenic substrate gives blue coloured DNA bands on the gel. Answer: (c) The presence of chromogenic substrate gives blue coloured DNA bands on the gel Solution: The chromogenic-substrate blue colour belongs to the β-galactosidase insertional-inactivation method of selecting recombinants (blue = no insert), NOT to gel electrophoresis, so statement (c) is the false one.
- A.The process of extraction of separated DNA strands from gel is called elution
- B.The separated DNA fragments are stained by using ethidium bromide
- C.The presence of chromogenic substrate gives blue coloured DNA bands on the gel✓
- D.Bright orange coloured bands of DNA can be observed in the gel when exposed to UV light
Correct Answer
(C) The presence of chromogenic substrate gives blue coloured DNA bands on the gel
Solution & Explanation
Answer: (c) The presence of chromogenic substrate gives blue coloured DNA bands on the gel Solution: The chromogenic-substrate blue colour belongs to the β-galactosidase insertional-inactivation method of selecting recombinants (blue = no insert), NOT to gel electrophoresis, so statement (c) is the false one. The true statements: elution is extraction of separated DNA from the gel (p.168), DNA is stained with ethidium bromide, and bright orange bands appear under UV light (p.168). NCERT clearly attributes the blue colour to chromogenic substrate in the vector-selection section, not to gel staining. NCERT Reference: Ch 9, p.170, line(s) 14 — "inactivation. The presence of a chromogenic substrate gives blue"