Question

Spindle apparatus is formed during which stage of mitosis?
a. Prophase
b. Metaphase
c. Anaphase
d. Telophase

Answer 1

Hint: Spindle apparatus is responsible for separation of chromosomes during cell division. It is formed during prometaphase. Spindle apparatus is formed from centromere present in cell cytoplasm. It is the characteristic features of eukaryotic cells.

Complete answer:
The mitotic cell division is carried out in various stages. The stages are prophase, prometaphase, metaphase, anaphase, Telophase and finally cytokinesis. Prophase starts with condensation of chromosomes into sister chromatids. It is the most important event of prophase. Prometaphase starts abruptly with breakdown of nuclear membrane. Formation of spindle apparatus occurs during this stage. The spindle apparatus attach to the centromere and undergo active movement. The chromosomes inside form protein structures called kinetochores. Kinetochore microtubules emerging from the centrosomes at the ends of the spindle reach the chromosomes and attach to the kinetochores. Other spindle microtubules make contact with microtubules coming from the opposite pole.

In metaphase, chromosomes are aligned at the equator of the spindle, midway between spindle poles. The kinetochore microtubules attach sister chromatids to opposite poles of the spindle.
In anaphase, the sister chromatids separate to form two daughter chromosomes and each is pulled toward the spindle pole. The kinetochores microtubules get shortened and chromosome segregation occurs.

Anaphase, the stage of mitosis, occurs after the process of metaphase. In this phase, replicated chromosomes are split and the newly-copied chromosomes (sister chromatids) are moved to opposite poles of the cell. This process occurs because of rapid polymerization and depolymerisation of microtubules in spindle fibres.

In Telophase, two sets of daughter chromosomes arrive at poles of spindle and decadence. Nuclear membranes start to reform around them. The division of cytoplasm begins with contraction of contractile rings.

Hence, the correct answer is option (B).

Note: Spindle apparatus is involved in separation of chromosomes and its formation begins in prometaphase and binds to sister chromatids in metaphase. The microtubules in spindle apparatus are mainly involved in separation of sister chromatids. They undergo rapid polymerization and depolymerisation.