How many unique zygotes can a couple make?

Each person carries 23 pairs of  chromosomes in every cell that makes up their body, with the exception of gametes, which contain 23 SINGLE chromosomes. So when a sperm and egg meet, they then have 23 pairs. In the process of meiosis 'crossing-over' occurs, which means that the chromosomes get "shuffled". This means that the child can receive random traits not only from the parents, but also the grandparents. so there is about  2⁴⁶ possible pairings, excluding the risk for things such as Down-Syndrome