Question

‘XX’ is a phase of mitosis, in which the chromatin condenses into discrete chromosomes. During ‘XX’ phase, nuclear envelope breaks down and spindles forms at opposite ends of the cell Identify ‘XX’

• A. Interphase
• B. Anaphase
• C. Telophase
• D. Prophase

Answer 1

The correct option is D Prophase

Before entering cell division, a cell spends a period of its growth under interphase. It undergoes the following phases when in interphase:

• G1 Phase: This is the period before the synthesis of DNA.
• S Phase: This is the phase during which DNA synthesis takes place.
• G2 Phase: This is the phase between the end of DNA synthesis and the beginning of prophase.

Prophase is generally identified by the initiation of condensation of chromosomal material. The chromosomal material condenses to form chromosomes. The nuclear envelope breaks down and spindles start to assemble at opposite ends of the cell. Thus, 'XX' stage is prophase.

At metaphase, the microtubules start pulling the chromosomes with equal force and the chromosome ends up in the middle of the cell. This region is known as the metaphase plate. Thus, each cell gets an entire functioning genome.

At anaphase, splitting of the sister chromatids marks the onset of anaphase. These sister chromatids become the chromosome of the daughter nuclei. The chromosomes are then pulled towards the pole by the fibres attached to the kinetochores of each chromosome. The centromere of each chromosome leads at the edge while the arms trail behind it.

At telophase, the chromosomes that cluster at the two poles start coalescing into an undifferentiated mass, as the nuclear envelope starts forming around it. The nucleolus, Golgi bodies and ER complex, which had disappeared after prophase start to reappear.

Telophase is followed by cytokinesis, which denotes the division of the cytoplasm to form two daughter cells. Thus, it marks the completion of cell division.