Origin and Genetic Diversity of Pig Breeds


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.

Keywords: pig breeds; genetic diversity; wild boar; artificial selection

Figure 1.

Median joining network of 440 mitochondrial D‐loop sequences corresponding to worldwide pig and (WB) populations. It can be seen that Far Eastern Sus scrofa display higher levels of genetic diversity than their European counterpaarts (most European haplotypes are grouped in a single cluster). It is also worth to highlight that European and Near Eastern mitochondrial haplotypes in general do not cluster together suggesting that both populations have distinct origins.

Figure 2.

Genetic dissection of the relationships between several Sus scrofa population based on the structure analysis of microsatellite data. It can be observed that there are three major groups with European (red), Far Eastern (blue) and mixed (green) ancestry. EWB, European wild boar; AWB, Far Eastern wild boar; AFWB, African wild boar; NEWB, Near Eastern wild boar; SCAP, South and Central American local pigs; MEDLP, Mediterranean and Slav local pigs; ANGLP, Anglo‐Saxon local pigs; INTP, International pig breeds; AFLP, African local pigs and AP, Far Eastern local pigs. Reproduced from Ramírez et al. with permission from Oxford University Press.

Figure 3.

Three Y‐chromosome haplotypes have been identified in Sus scrofa so far, being distributed in two major lineages (HY1+HY2 and HY3) that diverged around 1.27 Mya. In this picture, Y‐chromosome haplotype frequencies at diverse Sus scrofa populations are shown. Abbreviations are indicated in the legend of Figure , with the exception of WAFP () and EAFP (). Noteworthy, in these two latter populations differences in haplotype frequencies are dramatic, suggesting that EAFP pigs were strongly introgressed with Far Eastern blood at the paternal level while WAFP did not.

Figure 4.

Frequencies of European (in red) and Far Eastern (in blue) mitochondrial cytochrome b haplotypes in diverse Sus scrofa populations (abbreviations as indicated in the legends of Figure and Figure ). It is worth to highlight the strong Far Eastern genetic signature in Anglosaxon, International and East African pig breeds.

Figure 5.

Haplotype structure around an intron 3 mutation at the insulin‐like growth factor 2 gene with causal effects on muscle growth and leanness. This plot shows the squared correlation (r2) between pairs of loci (colour intensity augments proportionally to r2 values). Haplotype blocks are underlined and the arrow points at the causative intron 3 mutation. Five haplotype blocks were detected, spanning 1, 2, 9, 4 and 0.8 kb respectively. The third block was the largest and contained the causative mutation. From Ojeda et al. with permission from the Genetics Society of America.



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Amills, Marcel, Clop, Alex, Ramírez, Oscar, and Pérez‐Enciso, Miguel(Sep 2010) Origin and Genetic Diversity of Pig Breeds. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0022884]