Final answer:
Option (A), The process during meiosis I in which homologous chromosomes line up side by side is called synapsis, facilitated by the synaptonemal complex, and essential for genetic recombination.
Step-by-step explanation:
During meiosis I, homologous chromosomes line up side by side, a process called synapsis. This event occurs in prophase I, where chromosomes condense and the nuclear envelope begins to break down, allowing homologous chromosomes to pair closely together.
The pairing is facilitated by a protein structure known as the synaptonemal complex. Synapsis ensures that the genes on the chromatids of the homologous chromosomes are precisely aligned, which is crucial for the subsequent process of crossing over, allowing the exchange of genetic material between chromosomes and introducing genetic diversity.
Therefore, the correct answer is A. Synapsis.