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Blowing the Horn

Scientists at AgResearch's Molecular Biology Unit at Otago University have identified the chromosome location of a gene that produces horns in sheep. The discovery means there are now three genes known to influence the growth of horns in animals -- the other two being in goats and in cattle.

AgResearch Molecular Biology Unit senior scientist Dr Grant Montgomery made the discovery while studying the genes that influence wool growth. Montgomery's wool research involves crosses between polled (hornless) Romneys and the horned Merino breeds. A result of the trials has been segregation of these cross-bred sheep with horns and those without, so it was a natural progression to use this resource for following and understanding horn inheritance.

Horns are a very visible characteristic, and it is therefore relatively straightforward for scientists to track the inheritance of the gene that influences horn growth. Montgomery has been the first to map this particular gene to sheep chromosome 10, and was able to show it was a different gene than the other two genes already discovered that influence horn growth. There are few horned sheep in New Zealand, aa horns can cause injury and affect the quality of meat and hides. The discovery will provide the basis for a DNA marker test to breed polled animals if required.

Comparison of the gene maps of sheep, cattle and goats suggests that the three genes affecting the horned/polled condition in these species are different. This might be expected, since the expression of horns in each species is different and there are likely to be many genes involved in the pathway to horn development.

The genes identified in goats and cattle are likely to be present in sheep, and could be associated with other genetic effects, such as the Drysdale gene. In the 1930s, Dr Francis Dry noticed that a common gene within the normally hornless Romney breed produced a horned sheep with a particularly hairy fleece, later recognised as the Drysdale breed.