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Human (Homo sapiens) Genome Browser Gateway
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About the Human Dec. 2013 (GRCh38/hg38) assembly (sequences)
Homo sapiens
(Graphic courtesy of CBSE)

UCSC Genome Browser assembly ID: hg38
Sequencing/Assembly provider ID: Genome Reference Consortium Human GRCh38 (GCA_000001405.15)
Assembly date: Dec. 2013
Assembly accession: GCA_000001405.15
NCBI Genome ID: 51 (Homo sapiens (human))
NCBI Assembly ID: 883148 (GRCh38, GCA_000001405.15)
BioProject ID: PRJNA31257

Search the assembly:

  • By position or search term: Use the "position or search term" box to find areas of the genome associated with many different attributes, such as a specific chromosomal coordinate range; mRNA, EST, or STS marker names; or keywords from the GenBank description of an mRNA. More information, including sample queries.
  • By gene name: Type a gene name into the "search term" box, choose your gene from the drop-down list, then press "submit" to go directly to the assembly location associated with that gene. More information.
  • By track type: Click the "track search" button to find Genome Browser tracks that match specific selection criteria. More information.

Download sequence and annotation data:

Assembly Details

The GRCh38 assembly is the first major revision of the human genome released in more than four years. As with the previous GRCh37 assembly, the Genome Reference Consortium (GRC) is now the primary source for human genome assembly data submitted to GenBank. Beginning with this release, the UCSC Genome Browser version numbers for the human assemblies now match those of the GRC to minimize version confusion. Hence, the GRCh38 assembly is referred to as "hg38" in the Genome Browser datasets and documentation. For a glossary of assembly-related terms, see the GRC Assembly Terminology page.

GRCh38 Highlights

  • Alternate sequences - Several human chromosomal regions exhibit sufficient variability to prevent adequate representation by a single sequence. To address this, the GRCh38 assembly provides alternate sequence for selected variant regions through the inclusion of alternate loci scaffolds (or alt loci). Alt loci are separate accessioned sequences that are aligned to reference chromosomes. This assembly contains 261 alt loci, many of which are associated with the LRC/KIR area of chr19 and the MHC region on chr6. See the sequences page for a complete list of the reference chromosomes and alternate sequences in GRCh38.
  • Centromere representation - Debuting in this release, the large megabase-sized gaps that represented centromeric regions in previous assemblies have been replaced by sequences from centromere models created by Karen Miga et al., using centromere databases developed during her work in the Willard lab at Duke University (now at the University of Chicago) and analysis software developed while working in the Kent lab at UCSC. The models, which provide the approximate repeat number and order for each centromere, will be useful for read mapping and variation studies.
  • Mitochondrial genome - The mitochondrial reference sequence included in the GRCh38 assembly (termed "chrM" in the UCSC Genome Browser) is the Revised Cambridge Reference Sequence (rCRS) from MITOMAP with GenBank accession number J01415.2 and RefSeq accession number NC_012920.1. This differs from the chrM sequence (RefSeq accession number NC_001807) provided by the Genome Browser for hg19, which was not updated when the GRCh37 assembly later transitioned to the new version.
  • Sequence updates - Several erroneous bases and misassembled regions in GRCh37 have been corrected in the GRCh38 assembly, and more than 100 gaps have been filled or reduced. Much of the data used to improve the reference sequence was obtained from other genome sequencing and analysis projects, such as the 1000 Genomes Project.
  • Analysis set - The GRCh38 assembly offers an "analysis set" that was created to accommodate next generation sequencing read alignment pipelines. To avoid false mapping of reads, duplicate copies of centromeric arrays and WGS on several chromosomes have been hard-masked with Ns. The two PAR regions on chromosome Y have also been hard-masked, and the Epstein-Barr virus sequence has been added as a decoy to attract contamination in samples. Two versions of the analysis set are available on our downloads page: one without the alternate chromosomes from this assembly, and one that includes them.

Chromosome naming conventions
UCSC has introduced some slight changes to the Genome Browser chromosome naming scheme with this release:

  • Haplotype chromosome, unplaced contig and unlocalized contig names now include their NCBI accession number (e.g., chr6_GL000256v2_alt)
  • The "v2" at the end of the accession number indicates the NCBI version number
  • Haplotype chromosome names consist of the chromosome number, followed by the NCBI accession number, followed by "alt"
  • Unlocalized contig names consist of the chromosome number, followed by the NCBI accession number, followed by "random"
  • Unplaced contig names (contigs whose associated chromosome is not known) consist of "chrUn" followed by the NCBI accession number

Pseudoautosomal regions
The Y chromosome in this assembly contains two pseudoautosomal regions (PARs) that were taken from the corresponding regions in the X chromosome and are exact duplicates:

chrY:10,000-2,781,479 and chrY:56,887,902-57,217,415
chrX:10,000-2,781,479 and chrX:155,701,382-156,030,895

Assembly statistics
For a detailed set of statistics about this assembly, see the GRCh38 GenBank record.

NumberHaplotypesUnplaced Contigs

unlocalized contigs42
unplaced contigs127

For more information about the files included in the GRCh38 GenBank submission, see the GRCh38 README. Bulk downloads of the sequence and annotation data may be obtained from the Genome Browser FTP server or the Downloads page. The annotation tracks for this browser were generated by UCSC and collaborators worldwide.


Miga KH, Newton Y, Jain M, Altemose N, Willard HF, Kent WJ. Centromere reference models for human chromosomes X and Y satellite arrays. Genome Res. 2014 Apr;24(4):697-707. Epub 2014 Feb 5.