Rainbow Trout Genome Sequenced: New Clues to Vertebrate Evolution

Scientists are continuing to make new discoveries by looking at the DNA of creatures throughout the animal kingdom. Now, they've managed to map the genetic profile of the rainbow trout, a fish whose relatively recent genetic history reveals new clues as to how vertebrates evolved.

In this case, the researchers examined the rate at which genes have evolved since a genome doubling event occurred in the rainbow trout occurred about 100 million years ago. This doubling event is different from most evolutionary processes involving mutations; it acts like the copied draft of a piece of writing that can be edited and recast without the risk of destroying the earlier version. Usually, the consequences of these doubling events are lost, since they can be cast out as a result of genetic changes in subsequent generations. But the doubling event in the trout occurred relatively recently, which means that scientists can now study it a bit more closely.

"In humans and most vertebrates the duplication events were older so there are fewer duplicated genes still present," said Gary Thorgaard, one of the researchers, in a news release. "Most of the duplicated genes get lost or modified so much that they are no longer recognizable as duplicates over time. In the trout and salmon we can see an earlier stage in the process and many duplicated genes are still present."

So what did they find? Using the genome sequence and gene expression data from the rainbow trout, the researchers discovered that roughly half of all protein coding genes have been deleted since its genetic doubling event. In addition, the trout has retained almost all of its microRNA genes, which help regulate gene expression.

"It seems that the rate of evolution can vary in different situations," said Thorgaard in a news release. "Some animals, like the lungfish and coelacanth, are 'living fossils' that have been around for hundreds of millions of years without changing very much. Others, like the polar bear, seem to have evolved quite recently. After the trout gene duplication, the process happened more slowly than it has in most other vertebrate animals, and we can still watch it going on."

The findings are published in the journal Nature Communications.