Question

the drug colchicine inhibits the formation of spindle fibers during mitosis. if you treat dividing plant cells with colchicine, what would you expect the result to be?
a the chromosomes are halved during cell division and the result is a cell that has half the number of chromosomes than it would normally have
b. the chromosomes do not pull apart in an orderly fashion during cell division and the result is two cells with unequal numbers of chromosomes.
c the chromosomes are separated during prophase and each of the four daughter cells receives a haploid number of chromosomes.
d. the chromosomes do not pull apart during cell division and the result is a cell that has double the number of chromosomes than it would normally have

Explanation:

Spindle fibers are crucial for chromosome separation during mitosis. If their formation is inhibited (by colchicine in this case), chromosomes cannot be pulled apart to opposite poles. Mitosis proceeds up to metaphase (where chromosomes are lined up at the equator) but then cannot complete anaphase (chromosome separation). So, the cell does not divide into two daughter cells. Instead, the cell ends up with double the number of chromosomes (since DNA replication occurs in S - phase before mitosis).

• Option A: Incorrect. Chromosomes are not halved in mitosis (that occurs in meiosis).
• Option B: Incorrect. There is no division into two cells as spindle - mediated separation is inhibited.
• Option C: Incorrect. Chromosomes are not separated in prophase, and mitosis results in two daughter cells (not four), and it is for somatic (diploid - maintaining) cells.
• Option D: Correct. As spindle fibers are needed for chromosome separation to opposite poles. Without them, after DNA replication (which still occurs before mitosis), the cell has double the chromosome number.

Answer:

D. The chromosomes do not pull apart during cell division and the result is a cell that has double the number of chromosomes than it would normally have