From Jungle to Coops
Introduction
It might not explain if the egg came first or the chicken, but a genetic study of chicken sorts out the sequence of domestication. Small dna changes are behind the domestication of red jungle fowl to its present avatar. Researchers from Uppsala University in Sweden reported more than 7,000,000 single nucleotide differences and almost 1,300 deletions in the genetic material during the domestication process. The "domestication" has been linked to changes in the thyroid receptor, a protein that controls the metabolism and reproductive timing of the chicken.
Source
Down To Earth, April 2010