Project Results

Brown coat color, the B Locus, in sheep is known to be recessive to black; however, the potential molecular cause(s) across various breeds have not yet been discovered. Based on evidence from other species, TYRP1 is hypothesized to carry mutations responsible for changes from black to brown pigment in sheep breeds raised for wool. In the present study, we investigated the TYRP1 gene by Sanger sequencing the coding regions across several sheep populations within the United States that contain black and brown individuals. We identified two SNPs associated with brown coat color (chr2:80,608,128G>T and chr2:80,611,700C>T) located within exon 3 and 4, respectively. The exon 3 SNP leads to an amino acid change from cysteine to phenylalanine (C290F) and the exon 4 SNP introduces a premature stop codon in the TYRP1 protein (R356X). These SNPs segregate by breed where R356X is found in Icelandics and Shetlands, C290F is found in Natural Colored Finewool and Finnsheep, and Romeldales and Romneys carry both mutations. The results from this study provide more insight into coat color genetics in sheep and will allow breeders to make more accurate breeding decisions to meet their wool markets. 

About This Project

Sheep come in a variety of different patterns and colors, with black or white individuals being the most common. Brown is another rarer option, often called Moorit. There are no genetic tests currently available for shepherds to identify moorit carriers. Our project aims to identify the genetic variants responsible for moorit in sheep using a candidate gene sequencing approach. Discovering the genetic basis for moorit will allow shepherds to make more informed breeding decisions in their flocks.

Ask the Scientists

What is the context of this research?

Moorit sheep are present in several domesticated sheep breeds such as the Romeldale, Merino, Finnsheep, and many others. While it is known that this is a recessive trait there has been no work to determine the molecular cause of this color in domesticated sheep breeds. Work done in mice, dogs, and Chinese pigs has shown changes within the Tyrosinase-related Protein (TYRP1) gene that result in brown color. A small study conducted in a wild sheep population discovered a mutation in TYRP1 that was associated with a light brown coat color. However, this mutation has not yet been studied in US sheep breeds raised specifically for wool production.

What is the significance of this project?

Shepherds have been selecting for various color and patterns in sheep for hundreds of years as evidenced by breed development. Most research to date on sheep color has focused on the Agouti gene, which determines the different patterns that are seen in various sheep breeds. TYRP1 is the most likely genetic cause of brown coat color based on evidence from mice and dogs. This project will be the first to sequence TYRP1 in sheep breeds bred specifically for wool production in the US. It is important to learn if the same mutation is responsible for brown across different sheep breeds indicating an early origin of brown color or if the breeds have developed brown color independently of each other. This project will provide more insight into our understanding of sheep coat color genetics.

What are the goals of the project?

The goal of this project is to sequence 30 unrelated individuals, approximately 15 black and 15 moorit, for the candidate gene, TYRP1, thought to control brown coat color. We want to determine the specific mutations in the DNA that are responsible for brown coat color. We hope to determine if the same mutation causing moorit is shared among breeds or if there are different mutations resulting in the same color. This project will provide sequencing data that we can use to determine a cost-effective genotyping technique that shepherds can use to make more informed breeding decisions.