  Quark and gluon jets traversing through a quark-gluon plasma not only lose
their energies but also can undergo flavor conversions. The conversion rates
via the elastic $q(\bar q)g\to gq(\bar q)$ and the inelastic $q\bar
q\leftrightarrow gg$ scatterings are evaluated in the lowest order in QCD.
Including both jet energy loss and conversions in the expanding quark-gluon
plasma produced in relativistic heavy ion collisions, we have found a net
conversion of quark to gluon jets. This reduces the difference between the
nuclear modification factors for quark and gluon jets in central heavy ion
collisions and thus enhances the $p/\pi^+$ and ${\bar p}/\pi^-$ ratios at high
transverse momentum. However, a much larger net quark to gluon jet conversion
rate than the one given by the lowest-order QCD is needed to account for the
observed similar ratios in central Au+Au and p+p collisions at same energy.
Implications of our results are discussed.
