(Top) Golden and normal Zebrafish

Washington, Dec. 16 (Reuters): A little striped fish has helped scientists begin to solve one of the biggest mysteries in biology ? which genes are responsible for differences in human skin, eye and hair colour.

The large, international team of scientists reported yesterday that they had found a gene that makes African zebrafish of a lighter-than-normal colour ? and say the same gene helps explain the light-coloured hair, skin and eyes of many Europeans.

While they stress that they have not found a genetic basis for race, they say just a tiny change in a single amino acid plays a major role in causing the distinctive light European colouring. The gene is called SLC24A5, Keith Cheng of Pennsylvania State University and colleagues said.

“Our results suggest that SLC24A5 explains between 25 and 38 per cent of the European-African difference in skin melanin index,” they wrote in today’s issue of the journal Science.

Cheng’s team was originally looking for genes involved in cancer. They were using zebrafish, a favoured tool of genetic researchers because they are small, reproduce quickly and are well understood.

They found a gene that appeared to make some zebrafish “golden” ? with lighter-than-usual stripes. Under a microscope, the skin of these fish have smaller, fewer structures called melanophores.

In people of European descent, pigment granules called melanosomes are fewer, smaller, and lighter than those from people of West African ancestry. The melanosomes of East Asians fall in between.

This suggested gene variations may be responsible and may be similar in vertebrates ? which include fish, mice and people.

Scientists know that more than 100 genes are involved in pigment production, so the process is complex. But most of the genes identified so far are found in unusual conditions such as albinism, which causes very light skin and eyes.

“...the genetic origin of the striking variations in human skin colour is one of the remaining puzzles in biology,” the researchers wrote.

Cheng’s team zeroed on SLC24A5. Penn State pharmacologist Victor Canfield found that all vertebrates have a version of the gene. They found that one version appears to be the “base” and is found in most people of African and East Asian descent.

The researchers injected the base human version into ”golden” zebrafish embryos and found it made them develop into normal dark-striped fish. This clinched the idea that the human gene was the equivalent of the fish gene.