Which term describes the fusion of two gametes to form a diploid zygote?

The fusion of two gametes to form a diploid zygote is called SYNGAMY.

Explanation:

During sexual reproduction process, exchange of DNA usually occur and this introduces diversity into the offspring that are produced. One of the ways by which exchange of DNA take place is called syngamy. Syngamy involves the bonding together of two sex cells leading to the formation of cell that has double amount of the chromosomes in the parent cells. The two cells that bond together are called gametes while the diploid cells formed is called zygote.  The major function of syngamy is creation of variation; the genotypes in the formed zygote differ from those of the gametes.  

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