The technique simply provides a host egg to contain the genetic material from the mother's egg, either before or after fertilisation by the father. The host egg really is just that – a host – because its nucleus – the part that determines the genetic make-up of a human being – would be entirely removed before the procedure took place. The host egg no longer contains its own nuclear DNA. What you're left with is an empty, functioning 'shell', which will be filled with the mother's genetic material.