The first true genre of rock and roll was a mixture of jazz, blues and country music called race music. It first popular in Midwest and Sister Rosetta Tharpe is sung the song that first gave rock and roll its name. You should have a look at this http://en.wikipedia.org/wiki/Rock_and_roll.
Late answer here Nightmare. Better late than never. Alan Freed only coined the term rock and roll. I found the answer in a song by the late great McKinley Morganfield, aka Muddy Waters. The lyric goes "the blues had a baby and they named it rock and roll".It began in the south as the blues. This part of the country was a melting pot of many types of blues, country, gospel, and rockabilly. Elvis's hip shake or Chuck Berry's duck walk wasn't anything new. It'd been going on for years. They were just the first to let it loose on the rest of the world. Then the blues moved to Chicago and became electrified, the Chess Records era. At this point the world was black and white. Here comes Chuck Berry, Howlin' Wolf (the list never ends) and BOOM! Technicolor. This found the ears of many a young guitarist in England, hence the British Invasion. This is a winded answer I know. Sorry. I've spent a lot of years studying this. You can take it to the bank.