GMAP Tutorial


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Overview of GMAP

GMAP, which stands for Genomic Mapping and Alignment Program, is a bioinformatics tool designed for the mapping and aligning of cDNA sequences to a genome. It is a standalone program that provides a fast and efficient way to process single sequences as well as large sets of sequences. GMAP is known for its accuracy in generating gene structures, even when dealing with polymorphisms and sequence errors, and it does not rely on probabilistic splice site models, making it versatile across different species.

The program operates with minimal startup time and memory requirements, which allows it to be used interactively against large genomes in about a second. This is a significant improvement over existing mapping programs that may require several minutes to start up. Additionally, GMAP can switch between different genomes without the need for a pre-loaded server dedicated to each genome, and it can run on computers with as little as 128 MB of RAM.

GMAP's high-throughput batch processing capabilities are enhanced by memory mapping and multithreading, provided that appropriate memory and hardware are available. The program's methodology includes a minimal sampling strategy for genomic mapping, oligomer chaining for approximate alignment, sandwich dynamic programming for splice site detection, and microexon identification with statistical significance testing.

One of the key features of GMAP is its ability to handle mapping and alignment tasks on genomes with alternate assemblies, linkage groups, or strains. This flexibility is crucial for research involving non-model organisms or populations with high genetic diversity.

In summary, GMAP is a powerful and versatile tool for researchers in genomics and transcriptomics, providing a fast and accurate way to align sequences to genomes.


To install GMAP, you will typically need to download the source code from the official repository and compile it on your system. The installation process may vary depending on the operating system you are using. It is important to follow the specific instructions provided in the documentation that comes with GMAP. Additionally, you may need to install dependencies required by GMAP before compiling the program.

Quick Start

Once GMAP is installed, you can begin using it by preparing your cDNA sequences and the reference genome you wish to map them to. The basic command structure for running GMAP involves specifying the reference genome and the sequence file. GMAP will then perform the mapping and alignment, outputting the results in a specified format.

Code Examples Of Popular Commands

Here are five popular commands that you might use with GMAP:

  1. Basic Mapping Command: This command maps a cDNA sequence file to a reference genome.

    gmap -d <genome_database> -f <output_format> <cDNA_sequences.fasta>
  2. Batch Processing: For processing multiple sequences in a batch, you can use the following command:

    gmap -d <genome_database> -f <output_format> --batch=<number_of_sequences> <cDNA_sequences.fasta>
  3. Multithreading: To utilize multiple CPU cores for faster processing, you can specify the number of threads:

    gmap -d <genome_database> -f <output_format> -t <number_of_threads> <cDNA_sequences.fasta>
  4. Splice Site Detection: GMAP can detect splice sites without probabilistic models, and you can adjust the sensitivity of detection:

    gmap -d <genome_database> -f <output_format> --splice=<detection_sensitivity> <cDNA_sequences.fasta>
  5. Microexon Identification: To identify statistically significant microexons, you can use the following command:

    gmap -d <genome_database> -f <output_format> --microexon-spliceprob=<probability_threshold> <cDNA_sequences.fasta>

These commands are just a starting point, and GMAP offers a wide range of options and parameters that can be customized to fit the specific needs of your research project.

In conclusion, GMAP is a robust tool for genomic mapping and alignment, offering speed, accuracy, and flexibility. Whether you are working with mRNA, EST sequences, or other types of cDNA, GMAP provides a comprehensive solution for your alignment needs.