Question

Doubling of the chromosome number may be achieved by:
A. Use of spindle inhibitors
B. Marker-assisted breeding
C. Fusion of unreduced gametes
D. Protoplast fusion
Choose the correct answer from the options given below:

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

Hint:

To Double chromosomes, you need to Block division (Inhibitors) or Add cells together (Fusion).

Answer 1

The Correct Option is A

Concept: Chromosome doubling is necessary to restore fertility in haploids or create polyploid plants. This can be done chemically, biologically, or through cellular manipulation.

Step 1: Chemical Inhibition (A).
The Use of spindle inhibitors (A) (like Colchicine or Trifluralin) is the most common method. By stopping the spindle fibers from pulling chromosomes apart during cell division, the cell ends up with a double set of DNA.

Step 2: Cellular and Genetic Fusion (C and D).
Fusion of unreduced gametes (C) occurs when gametes that failed to undergo meiosis properly ($2n$ instead of $n$) fuse, naturally doubling the chromosome count. Protoplast fusion (D) (Somatic hybridization) physically merges two cells into one, combining their chromosome sets.

Step 3: Eliminating Breeding Techniques.
Marker-assisted breeding (B) is a method for selecting plants with specific genes using DNA markers; it is a tool for selection, not a mechanism for changing the actual number of chromosomes in a cell.