Answer: Egg cells, or ova, are complete cells and have mitochondria. Spern cells are mobile packets of DNA, running on glucose and have no internal structure or organelles. A tightly-packed helical mitochondrial sheath surrounds part of the sperm tail. This is strange, however, because the sperm cell does not appear to produce energy by oxidative phosphorylation. Oxidative phosphorylation occurs in mitochondria. The sperm appears to produce all of its energy needs by glycolysis, which does not need mitochondria.
Sperm do not contribute very many mitochondria to the egg upon fertilization. So most people get their mitochondria from their mothers.
Answer: Yes the pre ejaculation contains sperm. That is why the pull out method does not always work, and you still can get pregnant. So use condoms or another birth control method. There are many to choose from but you can still catch an std so condoms or abstain is your best method.
Answer: Apparently it is possible in the time shortly after the vasectomy for the tubes to grow back together. After my procedure I was told to bring a couple of semen samples over the next couple of months for analysis.