Cell Cycle and Cell Division — NEET UG practice

1. To check Statement I, recall the sub-stages of prophase I.

Given that prophase I of meiosis has five sub-stages — leptotene, zygotene, pachytene, diplotene and diakinesis — the chromosomes keep condensing progressively through these stages.

2. Identify the last sub-stage of prophase I.

Since diakinesis is the final sub-stage of prophase I, this is the point where chromosome condensation is completed and the spindle apparatus is assembled to prepare homologous chromosomes for separation.

Therefore, by the end of prophase I, the chromosomes are indeed fully condensed, so Statement I is correct.

3. To check Statement II, recall which division of meiosis resembles mitosis.

Given that mitosis is an equational division (sister chromatids separate, chromosome number stays the same), and Meiosis I is a reductional division (homologous chromosomes separate, chromosome number is halved), Meiosis I does not resemble mitosis.

Hence, it is Meiosis II, not Meiosis I, that resembles mitosis because it is also equational in nature.

So, Statement II is false.

4. Combine both conclusions.

Since Statement I is correct and Statement II is false, the correct match is Option D.

1. Recall that the cell cycle is divided into Interphase and M Phase (Mitosis).

Given that interphase itself is divided into three sub-phases — Gap 1 ($G_1$), Synthesis (S), and Gap 2 ($G_2$) — the cell must pass through each of these before entering M phase.

2. Understand what happens in each sub-phase, in order.

Since the cell first grows and prepares for DNA replication in $G_1$ phase, then actually replicates its DNA in S phase, and then grows further and prepares for division in $G_2$ phase, the natural order is:

$$G_1 \rightarrow S \rightarrow G_2$$

3. Identify what completes the cycle.

As the cell has now duplicated its DNA and grown sufficiently, it proceeds to M phase, where actual nuclear and cell division (mitosis) occurs.

Therefore, the correct sequence is:

$$G_1 \rightarrow S \rightarrow G_2 \rightarrow M$$

Hence, the answer is Option D.

1. Recall what happens during $G_1$ phase.

Given that $G_1$ phase is the growth phase before DNA replication, the cell is metabolically active and continuously grows but does not replicate its DNA.

So, A matches II.

2. Recall what happens during S phase.

Since S stands for Synthesis phase, this is where DNA synthesis occurs and DNA content per cell doubles.

So, B matches III.

3. Recall what happens during $G_2$ phase.

Given that the cell must prepare its molecular machinery before division, proteins are synthesized while cell growth continues in $G_2$ phase.

So, C matches IV.

4. Recall what happens during M phase.

Since M phase is the mitotic phase, this is where actual cell division occurs.

So, D matches I.

Hence, the correct combination A-II, B-III, C-IV, D-I corresponds to Option D.