Hunt D M, Dulai K S, Cowing J A, Julliot C, Mollon J D, Bowmaker J K, Li W H, Hewett-Emmett D
Department of Molecular Genetics, Institute of Ophthalmology, University College London, UK.
Vision Res. 1998 Nov;38(21):3299-306. doi: 10.1016/s0042-6989(97)00443-4.
Although trichromacy in Old and New World primates is based on three visual pigments with spectral peaks in the violet (SW, shortwave), green (MW, middlewave) and yellow-green (LW, longwave) regions of the spectrum, the underlying genetic mechanisms differ. The SW pigment is encoded in both cases by an autosomal gene and, in Old World primates, the MW and LW pigments by separate genes on the X chromosome. In contrast, there is a single polymorphic X-linked gene in most New World primates with three alleles coding for spectrally distinct pigments. The one reported exception to this rule is the New World howler monkey that follows the Old World system of separate LW and MW genes. A comparison of gene sequences in these different genetic systems indicates that the duplication that gave rise to the separate MW and LW genes of Old World primates is more ancient than that in the howler monkey. In addition, the amino acid sequences of the two howler monkey pigments show similarities to the pigments encoded by the polymorphic gene of other New World primates. It would appear therefore that the howler monkey gene duplication arose after the split between New and Old World primates and was generated by an unequal crossover that placed two different forms of the New World polymorphic gene on to a single chromosome. In contrast, the lack of identity at variable sites within the New and Old World systems argues for the origin of the separate genes in Old World primates by the duplication of a single form of the gene followed by divergence to give spectrally distinct LW and MW pigments. In contrast, the similarity in amino acid variation across the tri-allelic system of New World primates indicates that this polymorphism had a single origin in New World primates. A striking feature of all these pigments is the use of a common set of substitutions at three amino acid sites to achieve the spectral shift from MW at around 530 nm to LW at around 560 nm. The separate origin of the trichromacy in New and Old World primates would indicate that the selection of these three sites is the result of convergent evolution, perhaps as a consequence of visual adaptation in both cases to foraging for yellow and orange fruits against a green foliage.
尽管新旧世界灵长类动物的三色视觉都是基于三种视觉色素，其光谱峰值分别在光谱的紫光（SW，短波）、绿光（MW，中波）和黄绿色（LW，长波）区域，但潜在的遗传机制有所不同。在这两种情况下，SW色素均由常染色体基因编码，在旧世界灵长类动物中，MW和LW色素则由X染色体上的不同基因编码。相比之下，大多数新世界灵长类动物有一个单一的X连锁多态基因，带有三个编码光谱不同色素的等位基因。该规则唯一已知的例外是新世界吼猴，它遵循旧世界的LW和MW基因分开的系统。对这些不同遗传系统中基因序列的比较表明，导致旧世界灵长类动物中MW和LW基因分开的基因复制比吼猴中的更为古老。此外，两种吼猴色素的氨基酸序列与其他新世界灵长类动物多态基因编码的色素相似。因此，吼猴的基因复制似乎发生在新旧世界灵长类动物分化之后，是由不等交换产生的，这种不等交换将两种不同形式的新世界多态基因置于一条染色体上。相比之下，新旧世界系统中可变位点缺乏一致性，这表明旧世界灵长类动物中分开的基因起源于单个基因的复制，随后发生分化，产生光谱不同的LW和MW色素。相比之下，新世界灵长类动物三等位基因系统中氨基酸变异的相似性表明，这种多态性在新世界灵长类动物中有单一的起源。所有这些色素的一个显著特征是在三个氨基酸位点使用一组共同的替代，以实现光谱从约530nm的MW向约560nm的LW的转变。新旧世界灵长类动物三色视觉的独立起源表明，这三个位点的选择是趋同进化的结果，也许是因为在这两种情况下，视觉适应都是为了在绿色树叶背景下寻找黄色和橙色水果。
