Scientists Identify Genetic Basis For The Black Sheep Of The Family

The typical coat color for the wild-type sheep is black with a pale belly but livestock breeders preferred uniform white coat colour domestic sheep. However,they are having problem in the sheep industry because the recessive black 'non-agouti' allele of the ASIP gene carried by white sheep is difficult to distinguish resulting in small number of black coat colour sheep in the flock. Therefore, scientists have taken initiative to determine the genetic differences at the ASIP locus in order aid the selection of white coat colour sheep.



Scientists at Commonwealth Scientific and Industrial research Organisation (CSIRO) Queensland Bioscience Precint in Australia has succeeded in identifying the allele that codes for coat colour in breed domestic sheep. The procedure involves investigation of the genetic architecture of the agouti signaling protein (ASIP) gene in several sheep breeds by sequencing the ASIP locus and measuring the gene expression. ASIP functions to regulate pigmentation in mice. It is used in this study to determine its role in expressing the coat colour in sheep.

The mechanisms of the study also involves the tandem duplication encompassing the ovine ASIP and two neighbouring genes, AHCX coding regions and ITCH promoter region. According to Dr. Belinda Norris, it was discovered that the ubiquitous expression of a second copy of ASIP coding sequence regulated by duplicated copy of the nearby ITCH promoter causes the white sheep phenotype. As for the recessive black sheep, it is expressed by a single copy ASIP gene with a silenced ASIP promoter (non-duplicated agouti alleles). The researches also studied the ASIP locus in ancient Barbary sheep and it was confirmed that, however, a single copy functional wild-type ASIP is responsible for its colour phenotype (tan body with pale belly).

It was noted by Norris, that this study will be a benchmark which aid the development of gene copy number. Besides, she stated that analysis methods in the mapping and association of heritable traits in livestock animals will be at ease as well as identifying the carrier of the black non-agouti allele. Moreover, occurence of dominant Agouti mutation also can be identified whether it occured as multiple or single events through this breakthrough.

Link to original source of article…
http://www.sciencedaily.com/releases/2008/07/080710174236.htm

By : Syikin 42101792