Final answer:
Prophase I is the stage in which chromosomes condense and the synaptonemal complex allows for the exchange of chromosomal segments between homologous chromosomes.
Step-by-step explanation:
Prophase I is the stage in which chromosomes begin to condense and become visible inside the nucleus. During this stage, the synaptonemal complex forms between homologous chromosomes, allowing for the alignment and exchange of chromosomal segments between non-sister chromatids in a process called crossing over. The pairs of homologous chromosomes are held together only at chiasmata, and they are called tetrads because the four sister chromatids of each pair of homologous chromosomes are now visible.