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NZ tech used in global sheep genetics research

15 May, 2012

New Zealand science and technology has been used in recently published international research on the genetic history of sheep.

SNP chips screen sheep DNA for useful genes

High-density single nucleotide polymorphisms (SNP) chips (‘snip chips’) created in New Zealand are genetic selection tools that quickly and cheaply screen sheep DNA for useful genes. The SNP chip lab procedure, which can search for multiple traits across thousands of DNA markers at once, was recently made available after 2 decades of research. It can help farmers accurately select sheep with desirable genes for breeding but has found its way into the research field.

Single nucleotide polymorphisms (SNP) are point mutations or genetic variations that occur when a single nucleotide in a genome is altered.

Genetic consequences of domestication and evolution of sheep breeds

The study, published in the February 2012 issue of PLoS Biology, compared 49 034 DNA sites across the genome in 2819 sheep from 74 breeds around the world to pin down the genetic consequences of domestication and evolution of sheep breeds.

The research team found that when humans began farming sheep 11 000 years ago they began with a broad genetic base, with high diversity retained in most breeds. There is evidence that divergence was largely related to geographic dispersal from a domestication centre but with considerable evidence of crossing and recrossing among the diverging breeds. Sheep were first reared for meat. Then 4000–5000 years ago human-mediated specialisation for wool and milk began.

The authors of the study write that the transition from hunting to animal husbandry involved human control over the reproduction, diet and protection of animals. Through their domestication and subsequent selection, sheep have been moulded for specialised production of meat, wool, and milk and adapted to thrive in a diverse range of environments.

Regions of sheep genome that changed rapidly

The study identified regions of the sheep genome that appear to have changed rapidly in response to selection for genes controlling traits such as coat colour, body size, reproduction and, especially, the lack of horns – one of the earliest goals of selective breeding.

One of the authors, John McEwan, a senior scientist at AgResearch's Invermay campus and one of the SNP chips creators, says that sheep differ significantly from cattle and dogs, as these latter species have been subjected to large amounts of interbreeding.

High levels of genetic diversity in sheep

“The high levels of genetic diversity remaining in sheep mean that this species has considerable ability to respond to selection in any desired direction and also that many closely related breeds probably contain most of the variability of the related breeds.

“Some of the regions under selection reported in this study are related to wool characteristics, milking ability and reproduction and, as such, may have a direct impact on New Zealand sheep breeding. However, other regions will be related to the presence of ‘lack of wool’ or the presence of a fat tail and coat colouration and, as such, will have less impact in New Zealand.

Hope to find genetic regions with disease resistance

“The hope is some regions will be associated with disease resistance especially to internal parasites and footrot but much further work remains to be done in this regard, and this was not the major emphasis of this study.”

The breeds sampled included nine Argali sheep – a breed of huge wild animals that some New Zealand farmers have eyed because they grow to 180 kg. New Zealand animals represented in the study included Romney, Wiltshire, Texel, Arapawa and Dorset Horn breeds.

The SNP chips were developed in New Zealand and are widely used by Ovita (a consortium of Beef and Lamb New Zealand and AgResearch) on thousands of New Zealand rams. The technology is currently being commercialised by animal health company Pfizer.

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