Categories: Integument (skin) phene

Mendelian trait/disorder: yes

Disease-related: yes

Key variant known: no

Species-specific name: Carpet wool

Species-specific symbol: N

Species-specific description: Normal wool fibres are solid. In contrast, hair has a core (medulla) down the centre, filled with air. Sheep that are bred for wool have almost zero medullated (hairy) fibres. In 1931, a purebred Romney Marsh ram lamb with an exceptionally hairy fleece was born in New Zealand, on a property belong to a Mr Nielson. The lamb was given to Professor Dry at what is now Massey University, where a set of experimental matings showed that the extreme hairiness is due to an incompletely dominant allele, N, at an autosomal locus (Dry et al., 1940; Dry, 1955). NN homozygotes have approximately 65% by weight of medullated fibres. This is no use for traditional wool production, but it is ideal for carpet manufacture. In the following decades, the mutant allele was multiplied within a Romney background, giving rise to a new 'carpet-wool' breed: the Drysdale. Other carpet-wool alleles have appeared from time to time in New Zealand and Australia, also eventually giving rise to new breeds: the Tukidale and the Carpetmaster in New Zealand, and the Elliotdale in Tasmania. The New Zealand mutants appear to be alleles at a single locus, but there is some evidence that the Tasmanian mutation is at a different locus (Sides and Banks, 1987). The most comprehensive review of carpet-wool genetics is provided by Wickham (1978).