What process begins during the leptotene stage of prophase I?

During the leptotene stage of prophase I in meiosis, the process that begins is the condensation of duplicated chromosomes. This stage is characterized by the chromosomes becoming more visible as they start to coil and shorten, transitioning from a diffuse chromatin state to a more condensed form. While the chromosomes have already been duplicated during the S phase of the cell cycle prior to prophase I, the leptotene stage marks the initial step where these chromosomes begin to take on a compact structure, which is essential for the subsequent stages of meiosis.

It is important to note that while synapsis and the formation of bivalents occur later during the zygotene and pachytene stages, respectively, the leptotene stage primarily focuses on chromatids condensing in preparation for pairing. This condensation is crucial for the proper alignment and segregation of homologous chromosomes in later stages of meiosis.