Final answer:
After 1955, rock and roll became the dominant rhythm-oriented musical genre, influenced by a mix of gospel, blues, country, jazz, and R&B, and marked by icons like Bill Haley and Chuck Berry.
Step-by-step explanation:
Post-1955, the genre of rhythm-oriented music that dominated the American music scene was rock and roll. This newest musical genre saw a combination of electric instruments with the sounds of gospel, blues, country, jazz and R&B to craft a sound that was immensely popular with teenagers across the nation. Artists such as Bill Haley and His Comets and Chuck Berry were trailblazers, with Haley's "Rock Around the Clock" causing a sensation and Berry's performances blending rhythm and blues with rock and roll. The appeal of rock and roll to the youth was inextricably linked to its rebellious spirit and its ability to merge the racial lines of music during a time of significant cultural and societal changes.
In the 1940s, the musical landscape was very different, with several genres evolving from blues, jazz, and country music, eventually leading to Rhythm and Blues (R&B). However, by the 1950s, the electrification of R&B and the effects of innovative marketing targeted toward a younger, notably white, audience fostered the rise of rock and roll. This new form of music, while still deeply rooted in African American traditions, was now amplified through the technological advancements in recording and broadcasting, allowing it to reach a broader audience and fueling its rapid ascendancy.