QTL Analysis of Growth Traits on Chromosome 18 in Lori-Bakhtiari Sheep

In order to identify the segre QTL affecting growth traits on the end region of chromosome 18 in a Lori-Bakhtiari sheep population, 162 animals from 5 paternal half-sib families were taken to be studied. Phenotypic data included records of birth weight (BWT), weight at one month of age (W1), weaning weight (WWT), weight at six months of age (W6), chest circumference (GI6), body length (LG6), withers height at six months of age (HT6), weight at nine months of age (W9) as well as yearling weight (W12). Five sires along with their progeny were genotyped for 3 microsatellite markers in a candidate region on chromosome 18. QTL analysis was conducted using regression interval mapping with a single-QTL model. The individual family analysis suggested some QTLs segregating in families 1 and 5. In family 1, a QTL residing between CSSM18 and TMR1 markers was associated with BWT (117 cM), W1 (116 cM) and WWT (118 cM) (P<0.01). Also, in family 5, a QTL located between CSSM18 and TMR1 markers was linked to GI6 (114 cM) (P<0.01) and HT6 (113 cM) (P<0.05). Joint analysis of families 1 and 5 proposed some QTL related with W1 (P<0.01), WWT (P<0.05) and GI6 (P<0.01) being located at 113, 118 and 118 cM, respectively. A final analysis of all the families indicated a significant QTL affecting W6 (not previously verified) employing individual family analysis. In the joint analysis of all the families, QTL for W6 was positioned at 106 cM close to CSSM18 marker (P<0.05). An overlapping of the position of detected QTL with that of Carwell gene suggest that this gene is a strong candidate for the observed QTL effects.