A primary screen of the bovine genome for quantitative trait loci affecting twinning rate

An autosomal genome scan for quantitative trait loci (QTL) affecting twinni ng rate was carried out in the Norwegian Cattle population. Suggestive QTL were detected on Chromosomes (Chr) 5, 7, 12, and 23. Among these, the QTL p ositions on both Chr 5 and Chr 23 are strongly supported by literature in t he field. Our results also confirm previous mapping of a QTL for twinning t o Chr 7, but definitely suggest a different location of the QTL on this chr omosome. The most convincing QTL peak was observed for a region in the midd le part of Chr 5 close to the insulin-like growth factor 1 (IGF1) gene. Sin ce IGF1 plays an important role in the regulation of folliculogenesis, a mu tation search was performed by sequencing more than 3.5 kb of the gene in a ctual families. The sequencing revealed three polymorphisms in noncoding re gions of the gene that will be important in fine structure mapping and char acterization of the QTL.