Population Genomics Reveals Genetic Structure, Genomic Inbreeding, and Shared Homozygosity Hotspots in the Peruvian Paso Horse
This study utilizes high-density SNP markers to characterize the genomic diversity, population structure, and inbreeding patterns of the Peruvian Paso horse, revealing moderate overall diversity, distinct genetic clusters with varying effective population sizes, and shared homozygosity hotspots linked to genes involved in skeletal and neuronal development.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Horses have been shaped by humans for thousands of years, evolving from wild ancestors into the diverse breeds we see today. This transformation is written in their DNA, the biological instruction manual carried in every cell. When breeders select animals for specific traits, such as a unique way of walking or a particular build, they inadvertently change the genetic makeup of the population. Over time, this can lead to groups of horses that are genetically distinct from one another, even if they live in the same country. Scientists can now read these genetic instructions with high precision, looking for patterns that reveal how a breed was formed, how closely related the individuals are, and whether the population is losing its genetic variety. Understanding these patterns is crucial for preserving the health of domestic animals, ensuring that future generations remain robust and diverse.
In a recent study, researchers turned their attention to the Peruvian Paso horse, a breed celebrated for its smooth, four-beat gait and deep cultural roots in Peru. While this horse is famous for its movement and history, little was known about its genetic landscape across the southern regions of the country. To fill this gap, a team of scientists collected DNA samples from 143 horses in the departments of Lima, Ica, and Arequipa. They used a technology that scans tens of thousands of specific points in the genome, allowing them to compare the genetic makeup of each animal in detail. The goal was to map out the genetic structure of the breed, measure how much inbreeding might be occurring, and identify specific regions of the genome that have been heavily influenced by breeding practices.
The analysis revealed that the southern Peruvian Paso horse is not a single, uniform genetic group. Instead, the population splits into three distinct genetic clusters. This finding was surprising because the horses did not group strictly by where they lived; a horse from Lima could be genetically closer to one from Arequipa than to another from the same city. The researchers found that while these groups are different, they are still connected, with many horses showing a mix of ancestry from the different clusters. This suggests that breeders have historically moved animals between regions, keeping the gene flow active. Despite these divisions, the overall genetic diversity of the breed remains moderate, meaning the population has not lost a significant amount of its genetic variety, which is a positive sign for its long-term health.
However, the story changes when looking closer at specific groups. One of the three clusters showed signs of a much smaller breeding population in its history compared to the others. This group had higher levels of genetic similarity among its members, a pattern that often arises when a small number of ancestors contribute heavily to future generations. Another cluster displayed a higher frequency of long stretches of identical DNA, known as runs of homozygosity. These long stretches are like genetic fingerprints of recent inbreeding, indicating that some lineages within this group have been bred together more closely than others. Interestingly, the researchers found that while some groups had these signs of close breeding, the breed as a whole still maintained a healthy balance of genetic variation.
A particularly striking discovery was the identification of shared "hotspots" in the genome. These are specific areas where the DNA is identical across many horses, regardless of which genetic cluster they belong to. One such hotspot was found on chromosome 7 and appeared in all three groups. This suggests that this specific region has been preserved throughout the breed's history, possibly because it contains genes that are essential for the horse's unique characteristics. The genes in this shared region are involved in important biological processes, such as how cells communicate, how tissues are organized, and how the body grows. Other hotspots were unique to specific clusters and contained genes related to muscle development, nerve function, and the formation of cartilage and bone.
The study concludes that the Peruvian Paso horse has a complex genetic history shaped by both shared ancestry and distinct breeding lines. The presence of these specific genetic regions suggests that breeders have, perhaps unintentionally, selected for traits related to movement, body structure, and neurological function over many generations. By mapping these patterns, the researchers have provided a clear picture of the breed's current genetic health. The findings indicate that while some lineages have experienced recent inbreeding, the broader population retains enough diversity to remain viable. This genomic map now serves as a vital tool for breeders and conservationists, offering the knowledge needed to make informed decisions that will preserve the unique qualities of the Peruvian Paso horse for the future.
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