Final answer:
Synapsis is the initiating event in meiotic homologous recombination, essential for aligning homologous chromosomes and enabling crossing over, which is crucial for genetic variation.
Step-by-step explanation:
The initiating event in meiotic homologous recombination is synapsis. During prophase I of meiosis, as chromosomes condense, the nuclear envelope breaks down and homologous chromosomes come together. The synaptonemal complex forms between them, facilitating the tight pairing of the homologs known as synapsis.
Synapsis is essential for the aligned genes on the chromatids of homologous chromosomes, and it precedes the exchange of chromosomal segments - or crossing over - between non-sister homologous chromatids. Crossing over, observable as chiasmata under a microscope, is a critical source of genetic variation in meiosis.