Human-Time Lord Meta-Crisis

A Human-Time Lord Meta-Crisis was the term applied to a hybridised organism that combined the traits of a Time Lord and Human.

Only two have been known to exist - the "DoctorDonna" and the Meta-Crisis Doctor.

The DoctorDonna was an example of a Human who had a Human brain with a Time Lord consciousness. She had to be reverted to her Human self, as a Human brain could not hold a such a consciousness. This forced the Doctor to erase Donna Noble's mind of all knowledge pertaining to him. (DW: Journey's End) Despite this, Donna's latent consciousness still remained half-Time Lord, protecting her when the Master turned the world into copies of himself. Apparently, it also subconsciously guided her to buying a book for her grandfather, which led him and the Doctor to Joshua Naismith. (DW: The End of Time)

The Meta-Crisis Doctor seemed to be a mixture of the two races. He did not burn up, presumably having a Time Lord brain, but only had one heart and could not regenerate. He also took on quirks of Donna Noble, the Human with whom the Meta-Crisis occurred. (DW: Journey's End)