During anaphase of mitosis, what exactly is being pulled to opposite poles of the cell?
AHomologous chromosome pairs separating from each other
BSister chromatids separating after the cohesin holding them is cleaved
CReplicated chromosomes moving before DNA synthesis
DIndividual nucleotides being distributed to daughter cells
During S phase, each chromosome is duplicated into two identical copies called sister chromatids, held together at the centromere by a protein complex called cohesin. During anaphase of mitosis, cohesin is cleaved, releasing the sister chromatids from each other, and spindle fibers pull them to opposite poles. Each former chromatid becomes a full chromosome in the daughter cell. Homologous chromosome separation happens in meiosis I, not mitosis.
Question 2 True / False
Homologous chromosomes are separated from each other during anaphase of mitosis.
TTrue
FFalse
Answer: False
This is a critical distinction between mitosis and meiosis. During mitosis, it is sister chromatids (copies of the same chromosome) that separate — homologous chromosomes never pair up or separate during mitosis. Homologous chromosome separation occurs in anaphase I of meiosis. Confusing these two processes is one of the most common errors in understanding cell division.
Question 3 Short Answer
What role does the spindle apparatus play in mitosis, and how does it actually move chromosomes?
Think about your answer, then reveal below.
Model answer: The spindle apparatus is a structure of microtubule fibers that attaches to chromosomes at protein complexes called kinetochores. It physically moves chromosomes by controlled polymerization and depolymerization of microtubules — shortening the kinetochore microtubules pulls chromosomes toward the poles, while polar microtubules push the poles apart. The force is mechanical, not chemical signaling.
Understanding the spindle as a mechanical pulling machine (not a passive scaffold) clarifies why chromosome segregation errors occur when spindle dynamics are disrupted. Many cancer chemotherapy drugs (e.g., taxol, vincristine) work by interfering with microtubule dynamics, which halts mitosis and triggers cell death — which is why they target rapidly dividing cancer cells.