Unlocking Horse Y Chromosome Diversity

Area of Science:

• Genetics
• Animal Breeding
• Population Genetics

Background:

• Equine genetic variation is heavily influenced by intensive breeding programs over the last two centuries.
• The equine male-specific region of the Y chromosome (MSY) was first assembled in 2018, revealing 56 documented genes, making horses the most represented among 12 mammalian species studied.
• Modern horse populations exhibit remarkably low Y-chromosome genetic diversity, contrasting with high mitochondrial DNA variability across breeds.

Purpose of the Study:

• To provide a comprehensive overview of current knowledge regarding trends and prospects in equine Y-chromosome (MSY) variation.
• To investigate the causes behind the observed low genetic diversity in the equine Y-chromosome.
• To highlight the potential of the Y-chromosome as a genetic marker for addressing biodiversity and historical questions in horse breeds.

Main Methods:

• Review and synthesis of existing knowledge on equine MSY variation.
• Comparative analysis of equine MSY gene content with other mammalian species.
• Analysis of Y-chromosomal genotyping data and phylogenies across diverse horse breeds worldwide.

Main Results:

• Horses possess 56 documented MSY genes, the highest number among 12 mammalian species analyzed.
• Modern horse populations exhibit significantly low genetic diversity on the Y-chromosome.
• Selective breeding practices, relying on potentially flawed pedigree data, are identified as the primary driver of this reduced Y-chromosome variation.

Conclusions:

• The equine Y-chromosome, despite low diversity, serves as a powerful genetic marker.
• Detailed Y-chromosomal phylogenies aid in resolving genealogical, forensic, and population genetics questions.
• Understanding Y-chromosome variation is essential for conserving equine biodiversity and reconstructing breed histories, especially in light of selective breeding impacts.