Duplication of the apolipoprotein C-I gene occurred about forty million years ago.

Two human apolipoprotein C-I genes, one of which is believed to be a pseudogene, are located within the lipoprotein gene cluster on chromosome 19. Alignments were made between the apoC-I and the pseudoC-I' genes using a computer sequence editor. Particular Alu sequences may be found in one gene or in both: the proposal is that common Alu sequences (found in both genes) were present before the duplication of the C-I gene, whereas single Alu sequences (present in only one gene) were transposed afterward. Alu sequences of the C-I genes were also classified into Alu families. Common sequences belong to older families of Alu genes, whereas single sequences belong to younger families. Marked change in the apolipoprotein C-I gene began during early radiation of primate lineages. Retropositions of older Alu sequences occurred throughout the Paleocene and the Eocene periods. The numbering of uncommon substitutions in the six common Alu sequences gives a good estimate of the duplication time for the C-I gene (39 +/- 6 million years) at the end of the Eocene. After that, the other Alu sequences were transposed into each gene and further substitutions occurred to give the present form of the C-I genes in humans.