Cell Cycle and Cell Division

During the zygotene stage of prophase I of meiosis, the chromosomes start pairing together; this process of association is called synapsis.
The paired chromosomes are the homologous chromosomes, one from each parent.
Synapsis is accompanied by the formation of a synaptonemal complex, and the pair so formed is called a bivalent or tetrad.
The fusion of male and female gametes is syngamy, not synapsis.
Hence synapsis occurs between two homologous chromosomes.