Question

Which of the following causes mutation (not polyploidy)?

• A. Crossing over
• B. NaCl
• C. Colchine
• D. $\gamma$-rays

Answer 1

Answer: (D)

$\gamma$-rays

Crossing over is the process of exchange of genetic material between non-sister chromatids of homologous chromosomes to produce new genetic combinations or variations, no changes in chemical structure of the gene and hence no mutation. Colchicine disrupts the normal sequence of a nuclear division and induces somatic doubling by inhibiting microtubule formation which in turn prevents the spindle formation and thereby prevents the chromosomes from moving apart during cell division (either mitosis or meiosis). This results in is a cell with doubled chromosome number; the polyploidy, not mutation. NaCl affects the packaging of DNA; DNA is present as highly compact and bent interwound states at high salt concentration and as much more open and loosely interwound structure under low salt concentration, but no mutations. $\gamma$-rays are ionizing radiations that can penetrate deep in cell and cause chromosomal aberrations by introducing chromosomal breaks, alteration of nitrogenous bases, or by initiating the chain of chemical reactions. The correct option is D.