  $\textbf{Background:}$ High mutability of HIV is the driving force of
antiretroviral drug resistance, which represents a medical care challenge.
  $\textbf{Method and Model Equation:}$ To detect the mutability of each gene
in the HIV-1 genome; a mathematical analysis of HIV-1 genome is performed,
depending on a linear relation wherein the probability of spontaneous mutations
emergence is directly proportional to the ratio of the gene length to the whole
genome length. \begin{equation*} {P_g}{S_i} =\frac{g}{G} \end{equation*}
  $\textbf{Results:}$ $\textbf{tat}$, $\textbf{vpr}$ and $\textbf{vpu}$ are the
least mutant genes in HIV-1 genome. Protease $\textbf{PROT}$ gene is the least
mutant gene component of the polymerases $\textbf{pol}$.
  $\textbf{Conclusion:}$ $\textbf{tat}$, $\textbf{vpr}$ and $\textbf{vpu}$ are
the best candidates for HIV-1 recombinant subunit vaccines or as a part of
$\textit{prime and boost}$ vaccine combinations. Also; the protease
inhibitor-based regime represents a high genetic barrier for HIV to overcome.
