XYY syndrome is a rare mutation, in which a male child is born with an extra Y chromosome ... receiving literally a double-dose of masculinity. In adulthood, XYY men tend to be very tall and thin with severe acne problems. Some studies allege that XYY men tend to be of sub-normal intelligence with a penchant for criminal behaviour, but other studies contradict this. We can do without the assistance of people like Phil Donahue, who devoted an episode of his TV show to scaring several young mothers with 'evidence' that their XYY sons would grow up to be serial killers.
'The XYY Man' was originally a novel by Kenneth Royce, adapted by Ivor Marshall (and directed by Ken Grieve) as a 3-part serial which ran on Granada TV in July 1976. Stephen Yardley, an odd-looking actor with a gangly physique, gives a fascinating performance as 'Spider' Scott, a cat burglar whose criminal behaviour is down to his double Y chromosome. After his latest arrest by Sergeant Bulman and Constable Willis, 'Spider' is recruited for a job with a top-secret British intelligence bureau. (No, not M.I.5: this outfit is so hush-hush, they haven't even got a name.) Supposedly, Spider's extra chromosome gives him a uniquely criminal mind, enabling him to come up with all sorts of devious strategems that a normal operative couldn't anticipate. Spider agrees to carry out a mission for his new spymasters, but he's aware of a catch: if Spider gets caught, his criminal background will give Her Majesty's Government a plausible excuse to deny any knowledge of his actions.
Yardley is excellent in the 3-part mini-series, as a protagonist who is genetically incapable of going straight. He's well-supported by Don Henderson as his handler, the perpetually glove-wearing Bulman. In 1977, 'XYY Man' returned as a 10-episode series. Henderson reprised his role (now promoted to Detective Inspector) in 'Strangers', and then once again (with a much mellower personality) as a free-lance 'tec in 'Bulman'.
I can't vouch for all the genetic claims in 'XYY Man', but this is a very enjoyable series.
