Final answer:
In Prophase I of meiosis, the chromosomes condense and homologous chromosomes pair up to form tetrads, during which crossing over occurs, leading to genetic recombination.
Step-by-step explanation:
In Prophase I of meiosis, the replicated chromosomes condense, the homologous chromosomes form bivalents, and crossing over occurs. This phase is marked by several critical events that distinguish it from other phases of cell division. Chromosomes first become visible under a microscope as they condense. As the nuclear envelope breaks down, homologous chromosomes come together in a process called synapsis, forming a structure known as a tetrad.
The synaptonemal complex, a protein scaffold, forms between homologous chromosomes to support the exchange of genetic material, an event known as crossing over. This process results in the recombination of genetic material, leading to genetic diversity in the offspring. Ultimately, crossing over and the subsequent segregation of chromosomes contribute to the genetic variation essential for evolution.