Method and apparatus for the coding and selective access of compressed genomic sequence data produced by genomic sequencing machines. The coding process is based on aligning sequence reads with respect to pre-existing or constructed reference sequences, on classifying and coding the sequence reads by means of sets of descriptors, and further partitioning the descriptor sets into access units of different types. Efficient selective access to specific genomic regions with the guarantee of retrieving all sequence reads mapped to those regions, is provided by: signaling the type of data mapping configuration used to store or transmit the descriptor sets, determining the minimum number of access units that need to be retrieved and decoded to access a genomic region, providing a master index table that contain all information for optimizing the data access process.