The joining of a male reproductive cell (sperm) with a female reproductive cell (egg) is called fertilization.

Here's a breakdown:

* Sperm: A male reproductive cell that carries half of the father's genetic material.

* Egg: A female reproductive cell that carries half of the mother's genetic material.

* Fertilization: The process where the sperm and egg fuse together, combining their genetic material. This results in a single cell called a zygote, which contains a full set of chromosomes (half from the mother and half from the father).

Fertilization is a crucial step in the process of sexual reproduction. It marks the beginning of a new life.