Origin and Genetic Diversity of Pig Breeds

Abstract

Genetic and archaeological findings suggest that pig domestication began about 9000–10 000 YBP at multiple sites across Eurasia, followed by their subsequent spread at a worldwide scale. Development of local types throughout the centuries led to the foundation, mostly during the nineteenth century, of current modern breeds with defined phenotypes and production abilities. Extensive intercrossing markedly increased the gene pool of these founder populations. For instance, it is well known that many European pig breeds carry Far Eastern haplotypes at high frequencies because of an ancient introgression with Chinese swine. Since then, artificial selection, genetic bottlenecks and inbreeding have significantly modified the allelic diversity of pig breeds. In the next future, state‐of‐the‐art scientific advances as well as conservation programmes will be fundamental to preserve the genetic reservoir of pig breeds as well as to exploit it in the context of artificial selection schemes. Key Concepts: Pigs were domesticated at multiple locations across Eurasia. Exploratory and commercial journeys favoured the dissemination of European and Far Eastern pigs into Africa and America. England, United States and China were the main centres of breed development during the eighteenth to nineteenth centuries. Genetic variation of pigs has been shaped by the complex interplay of artificial selection, population admixture, inbreeding and genetic drift. Artificial selection is evolution but an accelerated pace; therefore, by comparing breeds that have undergone distinct selective pressures we can glimpse the molecular basis of adaptation. Approximately 20% of local pig breeds face extinction because of dramatic decreases in their census or extensive intercrossing with foreign populations. New genotyping and sequencing technologies will revolutionise knowledge on patterns of diversity in livestock species, including pigs.

Genetic structure, relationships and admixture with wild relatives in native pig breeds from Iberia and its islands

“…The weak differentiation between wild and domestic pig populations found in our study was not completely unexpected, since signs of admixture between these populations have been reported in the past, based on both microsatellite markers [41] and mitochondrial DNA [16]. Indeed, it has been suggested that recurrent backcrossing between domestic animals and their wild relatives is a common event in different species, contributing perhaps to increased genetic diversity [42].…”

Mining the pig genome to investigate the domestication process

“…However, these haplotypes segregated at similar frequencies, thereby making it impossible to discern the paternal ancestry of modern European swine breeds. The variation of pigs has been also analyzed with microsatellites (reviewed in Amills et al, 2010), but these analyses generally occur on a regional scale because the genotyping of these nuclear markers is time consuming and laborious. Such studies have detected a postglacial demographic expansion signature in European wild boars and have highlighted that, in contrast with previous mitochondrial analyses, the status of Italy as a primary domestication site is doubtful (Scandura et al, 2008).…”

“…Many of these breeds have become cosmopolitan given their excellent growth and reproductive abilities. Often, these breeds have replaced less productive local varieties, occasionally bringing local breeds to extinction (Amills et al, 2010). Without a doubt, this practice has reduced the gene pool of the porcine species to an important extent.…”

Identification of genome-wide copy number variations among diverse pig breeds by array CGH

“…Genetic and archaeological findings suggest that pig domestication began about 9000–10000 years before present (YBP) at multiple sites across Eurasia, followed by their subsequent spread at a worldwide scale [1]. Historically, Europe and China are two major areas of pig breeding [2].…”

“…Historically, Europe and China are two major areas of pig breeding [2]. Over the past centuries, pigs have shown marked differences between these two areas, even if many European pig breeds carry far Eastern haplotypes at high frequencies because of an ancient introgression with Chinese swine [1]. The Chinese pigs differ significantly from European pig breeds such as the Large White for many traits including fatness and ear traits [3-5].…”