Sexual reproduction can be defined as the sort of reproduction by which each organism arises from the fusion of two cells. This generally implies, with some exceptions, that each organism has two parents.

This description might sound trivial it is however not at all. Before the appearance of sex, organisms reproduced solely by division. One cell divided into two cells, no partners, no fusion, just simple cell division. This simple cell division is still here. In fact, the trillions of cells that make up your body are all the descendants of a single cell that underwent several dozens of cell divisions. Surprisingly, most multicellular, as well as, many unicellular organisms reproduce by sex. We might take it thus for granted but this course will show you that it is a rather peculiar and enigmatic process.