Final answer:
Synapsis is the process that forms a bivalent of 4 sister chromatids in meiosis, with the separation of these chromatids occurring during anaphase II of meiosis II, resulting in haploid gametes.
Step-by-step explanation:
The process that produces a bivalent of 4 sister chromatids that will separate later in meiosis is C) Synapsis. During DNA duplication of the S phase, each chromosome becomes composed of two identical copies known as sister chromatids which are held together at the centromere.
Early in prophase I of meiosis, homologous chromosomes undergo synapsis, forming a tight pairing. An exchange of chromosome segments between non-sister homologous chromatids, known as crossing over, occurs soon after. This is visually identified by the presence of chiasmata. The separation of sister chromatids occurs during anaphase II of meiosis II, leading to the formation of gametic combinations, each containing a haploid set of chromosomes.