London: Scientists have identified the genetic mutation that causes some chickens to lay blue eggs. The blue egg produced by some chickens is prettier and some say tastier and cleaner - than the traditional brown one – and now, thanks to scientists from The University of Nottingham, we know what caused the eggs in some breeds to turn this unusual colour. The team has identified the genetic mutation which first produced the blue egg in native South American chicken, the Mapuche fowl, and their European descendants, Araucana between 200 and 500 years ago.
The results could inform future research into agricultural breeding techniques if demand for the blue egg continues to grow. The scientists used the unique genetic resources conserved by heritage or 'fancy' poultry breeders to identify at fine resolution the exact location of the mutation in the genome in blue egg laying chicken. Further genomic study revealed the genetic cause of the blue coloured egg shell – surprisingly – an ancient harmless retrovirus in the domestic chicken. A retrovirus is a virus that, unlike most cellular organisms, carries its genetic blueprint in the form of ribonucleic acid (RNA).
It reproduces itself in a host cell using a special enzyme called 'reverse transcriptase' which transcribes RNA into deoxyribonucleic acid (DNA). This makes it possible for genetic material from a retrovirus to become permanently incorporated into the DNA of an infected cell. In this case, the retrovirus' effect was to trigger an accumulation of a green-blue bile pigment called biliverdin in the eggshell as the egg develops in the hen. "An unexpected find was the unique integration sites for the retrovirus in South American/European and Asian chickens. It shows the importance of viruses in shaping evolution and diversity of species," lead researcher, David Wragg, said.
"It's quite remarkable – retroviruses are generally considered to integrate at random locations in the genome, and so the chance of a retrovirus integrating at more or less the same location in two chicken populations is extremely low. "Moreover, when appearing in the population, the unusual egg colouration must have attracted the attention of the owners, who must be praised for having selected the trait in subsequent breeding," Wragg said.
