THERE is a tendency these days to tar all reality TV shows with the same dirty, sticky brush.

While you'll get no arguments from me that there are, indeed, too many of these shows sucking up quality airtime, write them all off at your peril.

Away from the cooking- singing-renovating waters, we drift languidly into more interesting territory, labelled "documentary" rather than "reality".

Family history series Who Do You Think You Are? is into its sixth Australian incarnation (SBS, Tuesdays, 7.30pm). So far, we have seen Andrew Denton and Rebecca Gibney trace their ancestral roots. The result, in both cases, has been some of the most moving television broadcast all year.

Denton uncovered devastating details of the family members who perished in Treblinka.

"It was a concentration camp?" an elderly relative asks him. "No, it was a death camp."

Gibney uncovered heartbreak, deception and tragedy going back to the 1850s. Bravely revealing her father's alcoholism and her mother's sexual abuse as a child, more horror was to come.

Her great-great grandfather suffered the deaths of two children and his wife in the space of just one week. Her great-grandfather was part of a volunteer army troop that razed the Maori village of Parihaka in the Taranaki Wars. And her grandmother was forced to give up and shun an illegitimate child, who later wrote in a never-sent letter of searching for a face that looked like hers.

Upcoming episodes will feature Jacki Weaver, Amanda Keller and Adam Goodes, among others.

Family trees are intoxicating for their mystery. Add celebrity to the mix, and you have one of TV's most captivating shows.