Did it only happen once?

What are the chances that two episodes of meiosis would occur at nearly the same time so that they could then be involved in sexual reproduction? Did mitosis evolve into meiosis once or many times? Surely you have to be able to believe anything if you believed that this could occur many times. However, if it only occurred once there would be a huge blockage in the evolutionary tree because there are both plants and animals that reproduce sexually. So did the sexual and asexual branches divide after this miraculous event?