In fact, all the food we eat relies somehow on the sun. Kinda makes me hungry. Humans do itch in space. Itching is a reaction to irritation of the skin, caused by insects, dust, air, etc. Although there aren't any mosquitoes in space, other stuff can cause itching.
Astronauts have a lot of trouble scratching their noses and ears during a space walk.
Each sperm and each egg have exactly half the number of chromosomes of normal cells. Which half is randomly determined for each cell. During fertilization this genetic material combines to complete one full set. This method ensures that each parent passes on some of their traits to the next generation without doubling the number of chromosomes present. You can see how that would be a problem.