Science - March 4, 2010

Genes of a feather flock together

Chicken genes are more organized that we thought. Genes that are frequently expressed can be found close together on chromosomes, and so can genes which are rarely expressed. The clustering of active genes is efficient and creates an evolutionary advantage under pressure from natural selection, believes Martien Groenen, professor of Animal Breeding and Genetics.

Other researchers have found similar organization in the genomes of humans and of mice, with clusters of high expression genes. High expression means that these genes make many copies of RNA coding for a particular characteristic. The genomes of humans, chickens and mice are very similar. 'We want to understand the principle of the genome', says Groenen.
Groenen's PhD student Haisheng Nie studied numerous chicken embryos and organs to find out when particular genes are expressed. 'With micro-arrays we could find out whether genes were switched on or off. And when they were expressed', says co-supervisor Richard Crooijmans. During this investigation Nie and Crooijmans found that active genes are often close together on the chromosome.     
'The genes are not next to each other by coincidence; there is an order to it', says Groenen. He guesses that the clustering of high expression genes makes them more accessible and is therefore efficient for the cell.
These insights do not have any immediate practical applications for the breeding of chickens. 'But with more knowledge of the genome we will be able to select more specifically and to make decisions about integrating genes with positive or negative characteristics in the breeding process', says Crooijmans.
Haisheng Nie will receive his PhD from Groenen on 8 March.