without problems. It has also been reported that clones can age prematurely and
have shorter telomeres that would be expected for a normal animal of the same age.
One solution to the ageing issue in cloned animals is to use adult stem cells as the
source of the nuclei. The use of porcine skin-derived stem cells has recently been
reported with successful generation of live piglets (Hao et al. 2009 ).
The very recent development of induced pluripotent stem (IPS) cells offers the
prospect of an increased efficiency of production of gene targeted domestic ani-
mals. IPS cells are cells that have been treated with a cocktail of transcription
factors found in ES cells and show high telomerase activity and totipotent proper-
ties. The technology was originally developed by Takahashi and Yamanaka ( 2006 )
who showed that the addition of just four transcription factors could re-programme
adult fibroblasts into pluripotent stem cells. Domestic animal IPS cells are currently
being produced for domestic species such as the pig (Wu et al. 2009 ).
2 The Potential of Detailed Animal Genomes
The genomes of many of the major veterinary species have been sequenced in the
last decade. In 2004 the dog became only the fifth mammal to have its entire genome
fully sequenced when the information was publicly released (Lindblad-Toh et al.
2005 ). This followed the earlier work in which molecular markers were used to
study genetic relationships between 85 domestic dog breeds and microsatellite
genotypes were used to correctly assign canine genomes to specific breeds (Parker
et al. 2004 ). An initial sequence and comparative analysis of the Abyssinian cat
genome was published in 2007 by Pontius and colleagues. An improved coverage
of the bovine genome was recently published (Zimin et al. 2009 ) and the genomes
of alpaca, sheep and pig are currently being sequenced (e.g. Humphray et al. 2007 ).
Beginning from approximately 300 mapped markers scattered on the 31 pairs of
autosomes and the X chromosome in 2001, the horse genome is now among the
best-mapped in domestic animals (Chowdhary and Raudsepp 2008 ). This includes
approximately 1.5 million single nucleotide polymorphisms (SNPs) from a variety
of breeds.
Although the cost of sequencing has fallen dramatically and the rate of sequenc-
ing risen rapidly since the start of sequencing the human genome, the coverage and
assembly of genomes often contain small gaps and numerous errors which will take
many years to improve. Thus work will need to continue to revise and refine the
genome maps of the various species.
Dogs provide important models of human disease as well as being an accessible
source of spontaneous diseases that can be used to test a variety of gene therapy
approaches. Such studies are enhanced by a detailed understanding of the canine
genome and the associations of specific diseases with different dog breeds (Karlsson
and Lindblad-Toh 2008 ). There are over 450 inherited diseases in the dog of
which at least half have very similar clinical presentations compared to man (Tsai
et al. 2007 ). Examples include a variety of breeds with haemophilia due to
216 D.J. Wells