About GeneCards GC Identifiers

GeneCards genes now have unique, informative and stable GeneCards identifiers (GC ids), provided by the GeneLoc Algorithm.

The id begins with GC, which is followed by the chromosome number, 'P' or 'M' for orientation (Plus or Minus strand), and approximate kilobase start coordinate.


is on chromosome X on the minus strand, starting at 87064 kilobases

Genes that are currently placed on a specific chromosome, but whose exact location on the chromosome is not yet known, receive a modified GC id, consisting of the chromosome and strand information, followed by a number, which indicates uncertain location, followed by a letter representing the specific contig containing the gene and the gene's kilobase position on that contig.

Genes located on the alternative reference sequences (haplotypes--see NCBI for a full explanation) ALT_REF_LOCI_8 on chromosome 4, ALT_REF_LOCI_1/ALT_REF_LOCI_2/ALT_REF_LOCI_3/ALT_REF_LOCI_4/ALT_REF_LOCI_5/ALT_REF_LOCI_6/ALT_REF_LOCI_7 on chromosome 6, CRA_TCAGchr7v2 on chromosome 7, or ALT_REF_LOCI_9 on chromosome 17 have a special GC id made up of the chromosome and strand information, followed by 'g' (CRA_TCAGchr7v2), 'i' (ALT_REF_LOCI_1), 'j' (ALT_REF_LOCI_2), 'k' (ALT_REF_LOCI_3), 'l' (ALT_REF_LOCI_4), 'm' (ALT_REF_LOCI_5), 'n' (ALT_REF_LOCI_6), 'o' (ALT_REF_LOCI_7), 'q' (ALT_REF_LOCI_8), or 'p' (ALT_REF_LOCI_9), the chromosome and strand information, followed by the gene's approximate kilobase start coordinate.

Genes whose positional information includes only the chromosome need a further modified GC id, which includes the chromosome number, followed by 'U9', indicating lack of strand and positional information, followed by five digits, assigned sequentially.

If an id needs to change in future versions because the previously reported position is refined, the superseded id remains associated with the gene, along with the new one, so it cannot be assigned to any other gene, and so that users can still find the gene by that id.

Developed at the Crown Human Genome Center, Department of Molecular Genetics, the Weizmann Institute of Science

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