What is synapsis in meiosis?

Synapsis is the process that occurs during prophase I of meiosis where homologous chromosomes pair up closely along their lengths. This pairing is crucial for genetic recombination, as it allows for crossing over to occur, leading to genetic diversity in the resulting gametes. During synapsis, proteins called synaptonemal complexes form between homologous chromosomes, which facilitates this close association and ensures proper alignment for recombination.

The other options relate to different stages or processes in cell division. The separation of sister chromatids happens later in meiosis, specifically during anaphase II. The formation of the spindle apparatus is essential for chromosome movement during division, but it occurs after synapsis. Duplication of chromosomes refers to interphase, which precedes meiosis and is not directly connected to the pairing of homologous chromosomes. Thus, the correct understanding of synapsis firmly aligns with the pairing of homologous chromosomes during prophase I, making it an essential concept in understanding meiosis and genetic variation.