Polymorphism of KRT83 and its association with selected wool traits in Merino-cross lambs

Keratins are structural proteins in the cortex of wool fibres. It is thought that variation in the keratin genes (KRTs) affects wool structure and characteristics. Polymerase chain reaction-single stranded conformational polymorphism (PCR-SSCP) analysis was used to investigate three regions of ovine KRT83. These regions were a portion of the promoter, the exon 2 region (including part of intron 1) and a region encompassing exon 3-4 (including all of exon 3, intron 3, exon 4 and part of intron 4). Initially, in 300 New Zealand Romney, Merino and White Dorper sheep obtained from 26 farms, one, two and four PCR-SSCP banding patterns were observed for these regions respectively. The exon 2 region contained two single nucleotide polymorphisms (SNPs) and the exon 3-4 region contained five SNPs. Investigation of the effect of the variation in the exon 3-4 region on variation in some wool traits were subsequently undertaken in 489 Merino × Southdown-cross sheep from seven sire-lines. The four variants identified in the original 300 sheep (designated A-D) and a new variant (E containing a new SNP) were observed with a frequency of 64.6%, 15.4%, 6.6%, 10.1% and 3.3%, respectively. General linear mixed-effects models (GLMMs) were used to investigate associations between the presence or absence of the variants and the wool traits, with a second set of models testing associations between common genotypes and those traits. The presence of A was associated with a decrease in fibre diameter standard deviation (FDSD) and coefficient of variation of fibre diameter (CVFD). The presence of C was associated with an increase in mean fibre diameter (MFD), mean fibre curvature (MFC) and prickle factor (PF), and a decrease in wool yield (Yield) [clean fleece weight (CFW)/greasy fleece weight (GFW) × 100%]. A trend for association between the presence of C and increased FDSD was also detected. The presence of D was associated with an increase in MFD and PF, and a decrease in Yield. The presence of E was associated with a decrease in CVFD. Genotype AD had a higher GFW and a lower Yield than AA, and AC and AD tended to have increased MFD compared to AA and AB. These results suggest that ovine KRT83 might be a useful candidate gene for improving wool traits