ROCK FAMILY TREES - The British rhythm-and-blues scene of the 1960s, when bands including the Yardbirds, John Mayall's Bluesbreakers and Manfred Mann, together with rock giants Cream and Led Zeppelin, transformed the sound of American blues into rock. The era also spawned such famous guitarists as Eric Clapton, Jimmy Page and Jeff Beck, and those commenting on the time include drummer Ginger Baker and bass players Jack Bruce and Tom McGuinness.