short bass breaks or brief solos during a concert. During a jazz concert, a jazz bassist may have a number of lengthy improvised solos, which are called "blowing" in jazz parlance. Among those who have spearheaded the bass guitar in jazz are Jaco Pastorius, Victor Wooten, and Marcus Miller. Fretted and fretless bass guitars One of the options for bass guitarists is whether to use an instrument with frets on the fingerboard or not. On a fretted bass, metal frets divide the fingerboard into semitone divisions (as on a guitar). The original Fender basses had 20 frets, but modern basses may have 24 or more. Fretless basses have a distinct sound, because the absence of frets means that the string must be pressed down directly onto the wood of the fingerboard as with the double bass. The string buzzes against the wood and is somewhat muted because the sounding portion of the string is in direct contact with the flesh of the player's finger. The fretless bass allows players to use the expressive devices of glissando, vibrato and microtonal intonations such as quarter tones and just intonation. In a small combo, the bass player may alone determine which type of bass to use and for which tunes. In a band with a bandleader, the leader may provide guidance on what tunes are best suited to each type of bass. Some bassists use both fretted and fretless basses in performances, according to the type of material they are performing. While fretless basses are often associated with jazz and jazz fusion, bassists from other genres use fretless basses, such as metal bassist Steve Di Giorgio. Bill Wyman takes credit for creating the first fretless bass guitar in 1961 when he converted an inexpensive Japanese fretted bass guitar by removing the frets. The first production fretless bass was the Ampeg AUB-1 introduced in 1966, and Fender introduced a fretless Precision Bass in 1970. In the early 1970s, fusion-jazz bassist Jaco Pastorius created his own fretless bass guitar by removing the frets from a Fender Jazz Bass, filling the holes with wood putty, and coating the fretboard with epoxy resin. Pastorius used epoxy rather than varnish to obtain a glass-like finish suitable for the use of roundwound strings, which are otherwise much harder on the wood of the fingerboard. Some fretless basses have "fret line" markers inlaid in the fingerboard as a guide, while