When we talk about meiosis I and II we talk about gametes formation.
The objective is to create cells with half DNA charge, called haploids.
At the meiosis I, in prophase I, crossing over happens and anaphase separated homologous chromosomes.
In the end, you still have cells with all DNA charges (2n).
To start meiosis II cells does not duplicate its DNA. When anaphase II happens sister chromatids split, and you end with half DNA charge cells. Haploids or (n).
