@staticmethod<EOL><INDENT>def _crossover_a_pair(chromosome_1, chromosome_2, mask):<DEDENT>
for _idx in range(len(chromosome_1)):<EOL><INDENT>if mask[_idx] == <NUM_LIT:1>:<EOL><INDENT>chromosome_1[_idx], chromosome_2[_idx] = chromosome_2[_idx], chromosome_1[_idx]<EOL><DEDENT><DEDENT>
!
        @brief Crossovers a pair of chromosomes.

        @param[in] chromosome_1 (numpy.array): The first chromosome for crossover.
        @param[in] chromosome_2 (numpy.array): The second chromosome for crossover.
        @param[in] mask (numpy.array): Crossover mask that defines which genes should be swapped.