You are correct. A sperm cell and an ovum are NOT alive. They are (or are not) VIABLE. That means that they COULD become a human life under the right circumstances. They do not have a human DNA signature, since humans have 46 chromosomes and zygotes have only 23. Cloning a zygote would only get you more zygotes. You could clone, theoretically, any complete human cell and in the process "create" an identical (unless there are errors!) human cell.