Q.An organism has two pair of chromosomes (i.e., chromosome number = 4). Diagrammatically represent the chromosomal arrangement during different phases of meiosis-II.

With a chromosome number of 4 (two homologous pairs), meiosis I has already reduced each resulting cell to 2 chromosomes (still double-stranded) before meiosis II begins, and meiosis II then simply separates the sister chromatids of those 2 chromosomes.

• Prophase II: each cell entering this stage carries 2 chromosomes, each still made up of two sister chromatids joined at a centromere (no longer paired as homologues, since meiosis I already separated the homologous pairs); the chromosomes condense again and the nuclear envelope breaks down by the end of this stage.
• Metaphase II: the 2 (double-stranded) chromosomes line up individually along the equator, each attached by its kinetochores to spindle fibres coming from both poles — unlike metaphase I, there are no bivalents here, since each chromosome now aligns on its own.
• Anaphase II: the centromere of each of the 2 chromosomes splits simultaneously, and the sister chromatids separate, so 2 single-chromatid daughter chromosomes move to each pole. …

A text description of the arrangement at each stage, in place of a drawing, is given below, tracking a single cell as it passes through meiosis II.

Before meiosis II begins, meiosis I has already taken the original diploid cell (chromosome number 4, i.e. two homologous pairs) through pairing, crossing over and the separation of homologues, producing two dyad cells, each now haploid with a chromosome number of 2 — but each of those 2 chromosomes is still made up of two sister chromatids joined at one centromere, since only the homologues, not the chromatids, were separated in meiosis I.

• Prophase II. Each cell carries 2 chromosomes, each still a two-chromatid structure. Unlike prophase I, there is no pairing of homologues here, since each cell now holds only one member of what was originally each homologous pair. The chromosomes condense once again, and by the end of this stage the nuclear membrane disappears, much as in an ordinary mitotic prophase.

• Metaphase II. The 2 (still double-stranded) chromosomes line up individually along the equator of the cell, at the metaphase plate. Microtubules from the two opposite spindle poles attach to the kinetochores of the sister chromatids of each chromosome — this time it is the two chromatids of a single chromosome that are gripped by fibres from opposite poles, rather than two homologues as in metaphase I. …

Step 1 — Determine the starting chromosome number and what meiosis I has already done: with 2n = 4 (two homologous pairs), meiosis I reduces each resulting cell to the haploid number, n = 2, with each of those 2 chromosomes still double-stranded (2 sister chromatids each), since only homologues — not chromatids — separated in meiosis I.

Step 2 — Track each meiosis-II stage for that one cell: Prophase II (2 double-stranded chromosomes re-condense, no homologue pairing since homologues are already separate), Metaphase II (the 2 chromosomes align individually at the equator, kinetochores attached to fibres from both poles), Anaphase II (each centromere splits, sister chromatids separate, 2 single-chromatid chromosomes move to each pole), Telophase II (nu …