Final answer:
The formation of a tetrad in spermatogenesis is called synapsis, which occurs during prophase I of meiosis.
Step-by-step explanation:
The formation of a tetrad of maternal and paternal chromosomes during spermatogenesis is called synapsis. This process occurs specifically during prophase I of meiosis, where homologous chromosomes come together and exchange segments of DNA in a process known as crossing over. This exchange of chromosomal segments is a crucial source of genetic variation and results in the formation of tetrads, which consist of four sister chromatids of each pair of homologous chromosomes.