British researchers discovers gene missing in humans

British researchers have discovered that a gene that makes cells in the eye receptive to light is missing in humans.

Whereas some animals like birds, fish and amphibians have two versions of this photoreceptor, mammals including humans only have one, researchers at the University of Manchester found, according to a report on the science website of AlphaGalileo on Wednesday.

The classical view of how the eye sees is through photoreceptive cells in the retina called rods and cones. But, recently, a third photoreceptor was discovered that is activated by a gene called melanopsin whose photoreceptor is not linked to sight but uses light for non-visual processes, such as regulating our day-night rhythms and pupil constriction.

Although the melanopsin gene is present in all vertebrates, the version in mammals was unusually different to that found in fish, amphibians and birds, according to the researchers.

"At first, we put this genetic anomaly between mammals and other vertebrates down to evolutionary differences. But we have now learnt that other vertebrates have a second melanopsin gene - one that matches the one found earlier in mammals and humans. The first melanopsin gene found in the other classes of vertebrates does not exist in mammals," Jim Bellingham who led the research was quoted as saying.

The researchers said it was not yet clear how the functions of the two melanopsins differ but having different cone genes or ' opsins' allows vertebrates to detect different wavelengths of light and allows them to see color.

They now hope to find out what losing one of these genes means for humans and whether the two melanopsin genes in non-mammals play similar or different roles in non-visual light detection and so provide clues as to the implications of only having one melanopsin gene.

Source: Xinhua