Final answer:
The diploid cell in a phase where sister chromatids are migrating to opposite poles is in anaphase. Following anaphase, telophase and cytokinesis conclude the cell division, resulting in haploid cells in meiosis or diploid cells in mitosis.
Step-by-step explanation:
Phases of Cell Division and Sister Chromatids
When a diploid cell with 2n=6 is in the phase of cell division where structures, which are pairs of sister chromatids (dyads), are migrating to opposite poles, the cell is in anaphase of either mitosis or meiosis II. During this phase, each pair of sister chromatids that were replicated during the S phase of interphase is pulled apart by the spindle fibers towards the opposite poles of the cell, ensuring that each new cell will receive an identical set of chromosomes.
After anaphase, during telophase and cytokinesis, the sister chromatids arrive at the poles and begin to decondense. Nuclear envelopes reform around the separated sister chromatids, which are now individual chromosomes, resulting in the formation of two distinct nuclei. Cytokinesis then divides the cytoplasm, forming two separate haploid cells if the process was meiosis or two diploid cells if the process was mitosis.
It is crucial to differentiate between the pair of sister chromatids and a homologous pair of chromosomes. Sister chromatids are identical copies of a single chromosome connected at the centromere after DNA replication. A homologous pair consists of chromosomes that are similar in shape, size, and gene content but come from different parents.