The formation of sperm (spermatogenesis) and the formation of pollen are both version of the same process, meiosis.  

Most animals and higher plants are diploid; they have two sets of chromosomes, one from their female parent, the other from their male parent – such cells are referred to as 2N (2 x one complete chromosome set). 

During the course of somatic (body) cell reproduction, each of these chromosomes is duplicated and one copy of each is segregated to each of the daughter cells through a process known as mitosis.  

If a 2N cell enters mitosis, the daughter cells that result will also be 2N.

The process of sexual reproduction involves the production of gametes.  Gametes are produced by meiosis. 

During meiosis, one 2N cell enters, and four 1N cells are produced. 

These 1N cells are known gametes.  Males produce sperm (which are smaller and generally motile) while females produce eggs (which are larger and immotile). 

In most animals, the 1N gametes never divide again, and will die after a short time unless an egg and a sperm fuse together in a process known as fertilization or syngamy to form a new 2N cell. 

Most plants are composed of cells that are 2N; and are known as saprophytes.  

The cells that give rise to male gametes are 2N; they proceed through meiosis to form four 1N pollen cells. 

In contrast to animals, these cells can, and in some plants, often do, divide through the process of mitosis. 

Some plants actually have a stable free living 1N form, known as a gametophyte.

In contrast to animals, the original pollen cells go through subsequent mitosis; there are multiple 1N nuclei within the pollen grain. 

Typically, one of the nuclei is used to form the 2N zygote.