What is it called when the gametes,

produced by the gametophyte

generation fuse to form a new

sporophyte generation?

Answer: It is called Alternation of generation.

Explanation:

Alternation of generation or metagenesis is a type of reproductive life cycle that occur in plants and algae that have distinct haploid sexual and diploid asexual reproduction stages. The diploid sporophyte undergoes meiosis to produce haploid reproductive cells called spores. The spores then develop into haploid male and female gametes (which is the gametophyte generation) fuse together to produce diploid zygotic sporophyte. This occur in some vascular plants, fungi, and protists.