Final answer:
Before the first meiotic division, homologous chromosomes undergo synapsis and crossing over during prophase I, which are essential steps for genetic recombination and reduction of chromosome numbers.
Step-by-step explanation:
Before the first division in meiosis, homologous chromosomes must undergo a critical process known as synapsis and crossing over. During prophase I, homologous chromosomes are brought close together, align precisely with each other, and form a synaptonemal complex. This pairing, called synapsis, supports the exchange of chromosomal segments between non-sister homologous chromatids, an event termed crossing over. The chiasmata that appear visually post-exchange mark the sites of such crossovers. This recombination event contributes to genetic diversity in the resulting gametes and is essential for the reduction of chromosome numbers that occurs following the first meiotic division.