Final answer:
During prophase I of meiosis, homologous chromosomes come together in a process called synapsis, facilitated by the synaptonemal complex, which allows for crossing over and genetic variation.
Step-by-step explanation:
During prophase I of meiosis, homologous chromosomes undergo a process known as synapsis, where they lie side by side. This contact is facilitated by the formation of a protein lattice known as the synaptonemal complex which holds the chromosomes together in perfect alignment. Synapsis allows for the homologous chromosomes to exchange DNA through a process called crossing over, which is a crucial source of genetic variation. After crossing over, the chromosomes are referred to as tetrads because they consist of four sister chromatids.