Which event occurs only during prophase i of the first meiotic division?

At the start of prophase I, chromosomes have duplicated already and during the prophase I, they coil and become thicker and shorter which can be seen under light microscope. After which, crossing-over follows and eventually the nucleolus disappears. In the cytoplasm, the meiotic spindle forms and the nuclear envelope disappears. This phase is considered as the longest phase of meiosis consuming almost 90 percent of the time for the two divisions.
The unique event that happens in prophase I of first meiotic division is the synapsis of homologous pairs.

Six amino acids have side chains that are polar but not charged. these are serine (ser), threonine (thr), cysteine (cys), asparagine (asn), glutamine (gln), and tyrosine (tyr). these amino acids are usually found at the surface of proteins, as discussed in the proteins 2 module.