Selection on MHC-linked microsatellite loci in sheep populations

Area of Science:

• Genetics
• Animal Breeding

Background:

• Microsatellites in the major histocompatibility complex (MHC) region are increasingly used to assess polymorphism in MHC genes.
• Understanding genetic diversity in domestic sheep (Ovis aries) and wild Mouflon (Ovis orientalis musimon) is crucial for conservation and breeding.

Purpose of the Study:

• To evaluate microsatellite diversity within and near the MHC in sheep breeds and Mouflon.
• To compare MHC-linked microsatellite variation with genome-wide microsatellites.
• To investigate factors influencing observed genetic diversity patterns.

Main Methods:

• Microsatellite genotyping was performed on multiple sheep breeds and wild Mouflon.
• Allelic richness and heterozygosity were calculated for MHC-linked and other microsatellite loci.
• Neutrality tests and comparisons with Hardy-Weinberg expectations were conducted.

Main Results:

• MHC-linked microsatellites displayed a significantly higher number of alleles compared to other genomic loci.
• Sheep breeds were categorized into high- and low-diversity groups, correlating with geographic origin (southern breeds more diverse).
• Observed heterozygosity was generally lower than Hardy-Weinberg expectations, and neutrality tests suggested non-neutral evolution at MHC-linked loci.

Conclusions:

• Geographic origin, not agricultural use, influences MHC microsatellite diversity in sheep breeds.
• The observed patterns suggest hitchhiking of MHC-linked microsatellites due to selection at nearby MHC genes.
• Selective breeding practices may have impacted genetic diversity within sheep populations.