Belongs to the glycosyltransferase 6 family. Could be the product of a pseudogene. According to PubMed:12499400, the human GGTA1 gene is an expressed pseudogene encoding non-functional truncated proteins containing the first four translated exons but missing the two catalytic exons. Although all exons expected to encode a functional GGTA1 of 371 residues are present in the human genome, all transcripts described encode truncated proteins that result from prematurely terminated transcription at the level of a strong transcriptional stop signal in the middle of intron 7. The premature transcriptional arrest of human GGTA1 gene leads to an ectopic splicing event and to the connection of a short intronic sequence downstream from translated exons. GGTA1 is active in marsupials, nonprimate placental mammals, lemurs and New World monkeys and synthesizes a carbohydrate antigen called 'alpha-gal epitope'. The alpha-gal epitope is present in large numbers on cell membrane glycolipids and glycoproteins. GGTA1 gene was inactivated in ancestral Old World monkeys and apes and, because of this, they lack alpha-gal epitopes and naturally produce an antibody called the 'anti-Gal antibody' which binds specifically to alpha-gal epitopes, is the most abundant antibody in humans and is responsible of rejection of mammalian xenografts.