As brain size usually increases with body size it has been assumed that the two are tightly constrained and evolutionary studies have therefore often been based on relative brain size (i.e. brain size proportional to body size) rather than absolute brain size. The process of domestication offers an excellent opportunity to disentangle the linkage between body and brain mass due to the extreme selection for increased body mass that has occurred. By breeding an intercross between domestic chicken and their wild progenitor, we address this relationship by simultaneously mapping the genes that control inter-population variation in brain mass and body mass. Loci controlling variation in brain mass and body mass have separate genetic architectures and are therefore not directly constrained. Genetic mapping of brain regions indicates that domestication has led to a larger body mass and to a lesser extent a larger absolute brain mass in chickens, mainly due to enlargement of the cerebellum. Domestication has traditionally been linked to brain mass regression, based on measurements of relative brain mass, which confounds the large body mass augmentation due to domestication. Our results refute this concept in the chicken.

Neuropeptide Y (NPY) receptors mediate a variety of physiological responses including feeding and vasoconstriction. To investigate the evolutionary events that have generated this receptor family, we have sequenced and determined the chromosomal localizations of all five presently known mammalian NPY receptor subtype genes in the domestic pig, Sus scrofa (SSC). The orthologs of the Y 1 and Y 2 subtypes display high amino acid sequence identities between pig, human, and mouse (92%-94%), whereas the Y 4 , Y 5 , and y 6 subtypes display lower identities (76%-87%). The lower identity of Y 5 is due to high sequence divergence in the large third intracellular loop. The NPY1R, NPY2R, and NPY5R receptor genes were localized to SSC8, the NPY4R to SSC14, and NPY6R to SSC2. Our comparisons strongly suggest that the tight cluster of NPY1R, NPY2R, and NPY5R on human chromosome 4 (HSA4) represents the ancestral configuration, whereas the porcine cluster has been split by two inversions on SSC8. These 3 genes, along with adjacent genes from 14 other gene families, form a cluster on HSA4 with extensive similarities to a cluster on HSA5, where NPY6R and >13 other paralogs reside, as well as another large cluster on HSA10 that includes NPY4R. Thus, these gene families have expanded through large-scale duplications. The sequence comparisons show that the NPY receptor triplet NPY1R-NPY2R-NPY5R existed before these large-scale duplications.

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The melanocortin-4 receptor (MC4R), a G-protein coupled receptor, is implicated in mediating the effect of leptin on food intake and energy balance. A previous candidate gene study reported an association between an MC4R missense mutation (Asp298Asn) and fatness, growth and feed intake in pigs. To assess this association further, we analysed the segregation of this missense mutation in relation to variation in fatness traits using a Wild Boar x Large White intercross. The Wild Boar and Large White founders were homozygous for different MC4R alleles. The MC4R was assigned to the expected region on pig chromosome 1. The statistical evaluation did not reveal any indication of a significant effect on fatness related traits in this pedigree.

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