Since centuries, the traits for production and disease resistance are being targeted while improving the genetic merit of domestic animals, using conventional breeding programs such as inbreeding, outbreeding, or introduction of marker-assisted selection. The arrival of new scientific concepts, such as cloning and genome engineering, has added a new and promising research dimension to the existing animal breeding programs. Development of genome editing technologies such as transcription activator-like effector nuclease, zinc finger nuclease, and clustered regularly interspaced short palindromic repeats systems begun a fresh era of genome editing, through which any change in the genome, including specific DNA sequence or indels, can be made with unprecedented precision and specificity. Furthermore, it offers an opportunity of intensification in the frequency of desirable alleles in an animal population through gene-edited individuals more rapidly than conventional breeding. The specific research is evolving swiftly with a focus on improvement of economically important animal species or their traits all of which form an important subject of this review. It also discusses the hurdles to commercialization of these techniques despite several patent applications owing to the ambiguous legal status of genome-editing methods on account of their disputed classification. Nonetheless, barring ethical concerns gene-editing entailing economically important genes offers a tremendous potential for breeding animals with desirable traits.

Keywords: animal breeding, clustered regularly interspaced short palindromic repeats /Cas9, genome editing, transcription activator-like effector nuclease, zinc finger nucleases.

1. Van Eenennaam, A.L. (2017) Genetic modification of food animals. Curr. Opin Biotechnol., 44: 27-34. [Crossref] [PubMed]

2. Gonen, S., Jenko, J., Gorjanc, G., Mileham, A.J., Whitelaw, C.B.A. and Hickey, J.M. (2017) Potential of gene drives with genome editing to increase genetic gain in livestock breeding programs. Genet Selection Evol., 49: 12. [Crossref]

3. Blasco, A. and Toro, M.A. (2014) A short critical history of the application of genomics to animal breeding. Livestock Sci., 166: 4-9. [Crossref]

4. Hickey, J.M., Bruce, C., Whitelaw, A. and Gorjanc, G. (2016) Promotion of alleles by genome editing in livestock breeding programmes. J. Anim. Breed. Genet., 133: 83-84. [Crossref] [PubMed]

5. Jenko, J., Gorjanc, G., Cleveland, M.A, Varshney, R.K., Whitelaw, C.B.A., Woolliams, J.A. and Hickey, J.M. (2015) Potential of promotion of alleles by genome editing to improve quantitative traits in livestock breeding programs. Genet. Sel Evol. 47: 55. [Crossref] [PubMed] [PMC]

6. Carroll, D. and Charo, R.A. (2015) The societal opportunities and challenges of genome editing. Genome Biol., 16: 242. [Crossref] [PubMed] [PMC]

7. Proudfoot, C., Carlson, D.F., Huddart, R., Long, C.R., Pryor, J.H., King, T.J. and Lillico, S.G. (2015) Genome edited sheep and cattle. Transgenic Res., 24: 147-153. [Crossref] [PubMed] [PMC]

8. Tan, W., Carlson, D.F., Lancto, C.A., Garbe, J.R., Webster, D.A., Hackett, P.B. and Fahrenkrug, S.C. (2013) Efficient nonmeiotic allele introgression in livestock using custom endonucleases. Proc. Natl. Acad. Sci., 110: 16526-16531. [Crossref] [PubMed] [PMC]

9. Lillico, S.G., Proudfoot, C., King, T.J., Tan, W., Zhang, L., Mardjuki, R., Paschon, D.E., Rebar, E.J. and Urnov, F.D. (2016) Mammalian interspecies substitution of immune modulatory alleles by genome editing. Sci. Rep. 6: 21645. [Crossref] [PubMed] [PMC]

10. Lillico, S.G., Proudfoot, C., Carlson, D.F., Stverakova, D., Neil, C., Blain, C., King, T.J., Ritchie, W.A. and Tan W. (2013) Live pigs produced from genome edited zygotes. Sci. Rep., 3: 1-4. [Crossref] [PubMed]

11. Thornton, P.K. (2010) Livestock production: Recent trends, future prospects. Phil. Trans. R. Soc. B., 365: 2853-2867. [Crossref] [PubMed] [PMC]

12. Henryon, M., Berg, P. and Sorensen, A.C. (2014) Animal-breeding schemes using genomic information need breeding plans designed to maximise long-term genetic gains. Livestock Sci., 166: 38-47. [Crossref]

13. Barabaschi, D., Tondelli, A., Desiderio, F., Volante, A., Vaccino, P., Vale, G. and Cattivelli, L. (2015) Next generation breeding. Plant Sci., 242: 7-11.

14. Barabaschi, D., Guerra, D., Lacrima, K., Laino, P., Michelotti, V., Urso, S., Vale, G. and Cattivelli, L. (2012) Emerging knowledge from genome sequencing of crop species. Mol. Biotechnol., 50: 250-266. [Crossref] [PubMed]

15. Perez-Pinera, P., Ousterout, D.G. and Gersbach, C.A. (2012) Advances in targeted genome editing. Curr. Opin Chem. Biol., 16: 268-277. [Crossref] [PubMed] [PMC]

16. Sun, N., Abil, Z. and Zhao, H. (2012) Recent advances in targeted genome engineering in mammalian systems. Biotechnol. J. 7: 1074-1087. [Crossref] [PubMed]

17. West, J. and Gill, W.W. (2016) Genome editing in large animals. J. Equine Vet. Sci., 41: 1-6. [Crossref] [PubMed] [PMC]

18. Wang, Z. (2015) Genome engineering in cattle: Recent technological advancements. Chromosome Res., 23: 17-29. [Crossref] [PubMed]

19. Isalan, M., Choo, Y. and Klug, A. (1997) Synergy between adjacent zinc fingers in sequence specific DNA recognition. Proc Natl Acad Sci., 94: 5617-5621. [Crossref] [PubMed] [PMC]

20. Certo, M.T. and Morgan, R.A. (2016) Salient features of endonuclease platforms for therapeutic genome editing. Mol. Ther., 24: 422-429. [Crossref] [PubMed] [PMC]

21. Boissel, S., Jarjour, J., Astrakhan, A., Adey, A., Gouble, A., Duchateau, P. and Shendure, J. (2014) MegaTALs: A rare-cleaving nuclease architecture for therapeutic genome engineering. Nucleic Acids Res., 42: 2591-2601. [Crossref] [PubMed] [PMC]

22. Rath, D., Amlinger, L., Rath, A. and Lundgren, M. (2015) The CRISPR-cas immune system: Biology, mechanisms and applications. Biochimie, 117: 119-128. [Crossref] [PubMed]

23. Sherkow, J.S. (2015) Law, history and lessons in the CRISPR patent conflict. Nature Biotechnol., 33: 256-257. [Crossref] [PubMed]

24. Laible, G., Wei, J. and Wagner, S. (2015) Improving livestock for agriculture-technological progress from random transgenesis to precision genome editing heralds a new era. Biotechnol. J., 10: 109-120. [Crossref] [PubMed]

25. Murray, J.D. and Maga, E.A. (2016) Genetically engineered livestock for agriculture: A generation after the first transgenic animal research conference. Transgenic Res., 25: 321-327. [Crossref]

26. Tan, W., Proudfoot, C., Lillico, S.G. and Whitelaw, C.B.A. (2016) Gene targeting, genome editing: From Dolly to editors. Transgenic Res., 25: 273-287. [Crossref] [PubMed] [PMC]

27. Bosch, P., Forcato, D.O., Alustiza, F.E., Alessio, A.P., Fili, A.E., Nicotra, M.F.O., Liaudat, A.C., Rodriguez, N., Talluri, T.R. and Kues, W.A. (2015) Exogenous enzymes upgrade transgenesis and genetic engineering of farm animals. Cell. Mol. Life Sci., 72: 1907-1929. [Crossref] [PubMed]

28. Wei, J., Wagner, S., Lu, D., Maclean, P., Carlson, D.F., Fahrenkrug, S.C. and Laible, G. (2015) Efficient introgression of allelic variants by embryo-mediated editing of the bovine genome. Sci. Rep., 5: 11735. [Crossref] [PubMed] [PMC]

29. Ciaran, M.L., Thomas, J.C., Eli, J.F. and Gang, B. (2015) Nuclease target site selection for maximizing on-target activity and minimizing off-target effects in genome editing. Mol. Ther., 3: 475-487.

30. Luo, J., Song, Z., Yu, S., Cui, D., Wang, B., Ding, F., Li, S., Dai, Y. and Li, N. (2014) Efficient generation of myostatin (MSTN) biallelic mutations in cattle using zinc finger nucleases. PloS One, 9: e95225. [Crossref]

31. Liu, X., Wang, Y., Tian, Y., Yu, Y., Gao, M., Hu, G., Su, F., Pan, S., Luo, Y., Guo, Z. and Quan, F. (2014) Generation of mastitis resistance in cows by targeting human lysozyme gene to β-casein locus using zinc-finger nucleases. Proc. R. Soc. B., 281: 20140619. [Crossref] [PubMed] [PMC]

32. Cui, C., Song, Y., Liu, J., Ge, H., Li, Q., Huang, H. and Zhang, Y. (2015) Gene targeting by TALEN-induced homologous recombination in goats directs production of β-lactoglobulin-free, high-human lactoferrin milk. Sci. Rep., 5: 10482. [Crossref] [PubMed] [PMC]

33. Ni, W., Qiao, J., Hu, S., Zhao, X., Regouski, M., Yang, M., Polejaeva, I.A. and Chen, C. (2014) Efficient gene knockout in goats using CRISPR/Cas9 system. PloS One, 9: e106718. [Crossref]

34. Qian, L., Tang, M., Yang, J., Wang, Q., Cai, C., Jiang, S., Li, H., Jiang, K., Gao, P. and Ma, D. (2015) Targeted mutations in myostatin by zinc-finger nucleases result in double-muscled phenotype in Meishan pigs. Sci. Rep., 5: 14435. [Crossref] [PubMed] [PMC]

35. Carlson, D.F., Tan, W., Lillico, S.G., Stverakova, D., Proudfoot, C., Christian, M., Voytas, D.F., Long, C.R. and Whitelaw, C.B. (2012) Efficient TALEN-mediated gene knockout in livestock. Proc. Natil. Acad. Sci., 109: 17382-17387. [Crossref] [PubMed] [PMC]

36. Hai, T., Teng, F., Guo, R., Li, W. and Zhou, Q. (2014) One-step generation of knockout pigs by zygote injection of CRISPR/Cas system. Cell. Res., 24: 372-375. [Crossref] [PubMed] [PMC]

37. Keefer, C.L. (2015) Artificial cloning of domestic animals. Proc. Natl Acad. Sci., 112: 8874-8878. [Crossref] [PubMed] [PMC]

38. Zhang, X., Li, W., Wu, Y., Peng, X., Lou, B., Wang, L. and Liu, M. (2017) Disruption of the sheep BMPR-IB gene by CRISPR/Cas9 in in vitro-produced embryos. Theriogenology, 91: 163-172. [Crossref] [PubMed]

39. Reyes, L.M., Estrada, J.L., Wang, Z.Y., Blosser, R.J., Smith, R.F., Sidner, R.A. and Paris, L.L. (2014) Creating class I MHC-null pigs using guide RNA and the Cas9 endonuclease. J. Immunol., 193: 5751-5757. [Crossref] [PubMed]

40. Li, P., Estrada, J.L., Burlak, C., Montgomery, J., Butler, J.R., Santos, R.M., Wang, Z.Y. and Paris, L.L. (2015) Efficient generation of genetically distinct pigs in a single pregnancy using multiplexed single-guide RNA and carbohydrate selection. Xenotransplantation, 22: 20-31. [Crossref] [PubMed]

41. Van Raden, P.M., Olson, K.M., Null, D.J. and Hutchison, J.L. (2011) Harmful recessive effects on fertility detected by absence of homozygous haplotypes. J. Dairy Sci., 94: 6153-6161. [Crossref] [PubMed]

42. Gholap, P.N., Kale, D.S. and Sirothia, A.R. (2014) Genetic diseases in cattle: A review. Res. J. Anim. Vet. Fishery Sci., 2: 24-33.

43. Hickey, J.M. (2013) Sequencing millions of animals for genomic selection 2.0. J. Anim. Breeding Genet., 130: 331-332. [Crossref] [PubMed]

44. Blendon, S., Gorski, M. and Benson, J. (2016) The public and the gene-editing revolution. New Engl J Med., 374: 1406-1411. [Crossref] [PubMed]

45. Braun, K. (2017), From Ethical Exceptionalism to Ethical Exceptions: The Rule and exception Model and the Changing Meaning of Ethics In German Bioregulation. Developing World Bioeth, 17: 146-156. [Crossref] [PubMed]