Paper 13: "The Evolution of Trichromatic Color Vision by Opsin gene Duplication in New World and Old World Primates

Howler Monkey

in contrast to other NW monkeys, the Howler monkey has separate MW and LW genes, thus conferring full trichromacy in both females and males - duplication in Howler monkey is more recent

5’ Flanking Regions in OW Primates

contains four Alu repeats immediately adjacent to the the point of sequence divergence between the MW and LW 5’ flanking regions → homology is restricted to the first 236bp

Alu Elements

alue repeats indicate that the DNA has been cut before and that that region of the DNA is possibly unstable - indication for a split

5’ Flanking Regions in NW Primates

sequence identity between the marmoset (NW) and humans LW sequences is substatial throughout their entire length - overall identity is 77% and there is no evidence of duplicated regions within either sequene

Homology between NW and OW

human sequence shows essentially no homology with the marmoset sequence beyond the first 236bp of upstream sequence

Origin of Divergence

absence of any homology beyond the first 236bp indicates that divergence must be the consequence of gene duplication and therefore identifies the break point for the gene insertion that gave rise to separate MW and LW genes in OW primates

Duplication of the X-linked Opsin Gene in the Howler Monkey

homology between Holer monkey and NW primates extends well past the 236bp found between OW and NW primates - indicates that duplication in Howler monkey differs from that in OW monkeys

→ duplication in this species must include the entire 5’-flanking region of the gene and the LCR

Activation of Opsin Genes

LCR interacts by a looping mechanism with the adjacent gene promoter to form a transcriptionally active chromatin domain

Activation of Different Opsin Genes in OW Monkeys

LCR region activates either MW or LW in each cell by a looping mechanism - chooses randomly

Opsin Activation in Howler Monkey

the presence of two LCRs in the Howler monkey would indicate that the mechanism of selective opsin gene expression may differ from that in Old World primates