During which prophase I phase does synapsis complete?

Synapsis is the process during prophase I of meiosis where homologous chromosomes pair up and become closely associated. This pairing is crucial for the exchange of genetic material through a process called crossing over. In the context of prophase I, synapsis reaches completion during the pachytene stage.

During the zygotene phase, the homologous chromosomes start to pair up, but it is during the pachytene phase that this process is fully realized. Each paired set of chromosomes is known as a tetrad, which consists of two homologous chromosomes, each made up of two sister chromatids. The completion of synapsis in pachytene allows for the formation of structures called chiasmata, where crossing over occurs, leading to genetic variation in the resulting gametes.

This is why the correct answer is pachytene. It is the stage where the chromosomes have maximally paired and genetic recombination is prepared to occur, setting the stage for further processes that lead to the eventual formation of gametes.