Advanced Placement (AP) Biology Practice Exam

What happens to the chromosomes during anaphase of mitosis?

1. They condense

2. They align at the equatorial plate

3. They are pulled apart

4. They decondense

The correct answer is: They are pulled apart

During anaphase of mitosis, the key event is that the sister chromatids, which are the duplicated chromosomes, are separated and pulled apart towards opposite poles of the cell. This separation is facilitated by the spindle fibers, which attach to the centromeres of the chromatids and help in their movement. As the chromatids are separated, each chromatid is now considered an individual chromosome, ensuring that when the cell divides, each daughter cell will receive an identical set of chromosomes. This critical step is essential for the accurate distribution of genetic material during cell division. Condensation of chromosomes occurs earlier in prophase, where they become more tightly packed to ensure proper segregation. Alignment at the equatorial plate happens during metaphase, where all chromosomes are lined up in preparation for separation. Decondensation takes place after mitosis is complete, during telophase, when the chromosomes begin to unravel back into a less condensed form as the cell starts to enter interphase. Hence, the process described in this scenario is specifically the separation of chromatids, characteristic of anaphase.