[Lazzi]

Lazzi asked the Naked Scientists:
   
How does sperm form?

Is it ready made, or prepared during sex?

What do you think?

[Nizzle]

From stem cells in the testes.

These stem cells undergo a specific cell division called Meiosis, which only occurs in the stem cells of sperm and stem cells of eggs. This causes that sperm or egg cells only have half the amount of DNA compared to a normal cell.
This is a continuing process in men so even when you typed your question, or now reading the answer, you're making little swimmers

[bumblebee]

Sperm form in the testes via meiosis, whereby haploid cells are made. Meiosis Simplified: prophase, metaphase, anaphase, telophase and it happens in two stages. They are always being produced..

[syhprum]

I understand they have a life of about two weeks and regardless of what R Baden-Powell said it is a good idea to get rid of the dead ones.