To become Wiccan, do I have to have an ancestor that was Wiccan?

Although some people might tell you so, the (vast) majority of pagans believe that you don't have to be a descendant of Wiccan or a witch in order to be one. Wicca is spiritual path and you decide what you believe in. Witchcraft is - as the name says - craft. Some people practise witchcraft and practise makes perfect, as they say. In order to be Wiccan, you don't have to practise witchcraft. They are two separate things. There's a popular phrase in the Wiccan communities: 'Not all Wiccans are witches, and not all witches are Wiccans'.