Tandem duplication of the GC gene. The 5' copy contains a TAA termination codon at position 398 and is expected to result in a product 27 amino acids long. The 3' copy contains a TAA termination codon at position 1947 and is expected to result in a product 541 amino acids long. (The complete protein is 670 amino acids long.) Nucleotide numbering is based on mRNA sequence with accession NM_079161.