Why Do Chromosomes Resemble the Letter X When Viewed During

Question

Why do chromosomes resemble the letter X when viewed during metaphase?
A) Because they all appear and function as X chromosomes at that stage.
B) Because there are two sister chromatids joined at a point in the middle (the centromere).
C) Because microtubules encircle and attach pairs of chromosomes to each other at the centromere.
D) Because each X-shaped structure is actually four chromosomes joined at the centromere.

Accepted Answer

During metaphase, the chromosomes have already duplicated and each chromosome consists of two identical sister chromatids attached at a point called the centromere. The X shape occurs when the sister chromatids are aligned in the middle of the cell, and the microtubules from the spindle fibers attach to the centromeres to pull the chromatids apart during cell division.