Meiosis II follows meiosis I without an intervening round of DNA replication. Its defining operation is the separation of sister chromatids from chromosomes that are already in haploid nuclei or cell compartments.

After meiosis I, each nucleus contains one homolog of each chromosome type, so it is haploid. However, each chromosome still consists of two sister chromatids.

The spindle geometry now resembles mitosis

During meiosis II, the sister kinetochores of each replicated chromosome attach toward opposite spindle poles. This is the same basic segregation geometry used in mitosis.

At metaphase II:

pole A ← [sister 1 | sister 2] → pole B

At anaphase II, the remaining cohesion holding sister chromatids together is released, and the sisters move to opposite poles.

Once separated, each former chromatid is an independent chromosome.

Meiosis II does not reduce ploidy again

The crucial counting distinction is:

after meiosis I:   haploid, replicated chromosomes

after meiosis II:  haploid, unreplicated chromosomes

Both states contain one homologous chromosome set. Meiosis II reduces DNA content per nucleus by separating sister chromatids, but it does not reduce the number of chromosome sets from $n$ to something smaller.

Meiosis II is therefore called an equational division with respect to ploidy.

One replication supports two divisions

The overall meiotic sequence is

S phase
   ↓
replicated diploid chromosomes
   ↓ meiosis I: homologs separate
haploid nuclei with replicated chromosomes
   ↓ no DNA replication
meiosis II: sisters separate
   ↓
haploid nuclei with unreplicated chromosomes

Starting from one diploid cell, two successive divisions commonly produce four haploid nuclear products, although later cell differentiation and cytokinesis vary among organisms.

The conceptual contrast between the two meiotic divisions is therefore simple but fundamental:

• meiosis I separates homologous chromosomes and reduces ploidy;
• meiosis II separates sister chromatids and preserves the already haploid ploidy.