Mapping the Naked Neck (<it>NA</it>) and Polydactyly (<it>PO</it>) mutants of the chicken with microsatellite molecular markers

<p>Abstract</p> <p>The bulked segregant analysis methodology has been used to map, with microsatellite markers, two morphological mutations in the chicken: polydactyly (<it>PO</it>) and naked neck (<it>NA</it>). These autosomal mutations show partial dominance for <it>NA</it>, and dominance with incomplete penetrance for <it>PO</it>. They were mapped previously to different linkage groups of the classical map, <it>PO </it>to the linkage group IV and <it>NA </it>being linked to the erythrocyte antigen <it>CPPP</it>. An informative family of 70 offspring was produced by mating a sire, heterozygous for each of the mutations, to 7 dams homozygous recessive for each locus. Three DNA pools were prepared, pool <it>PO </it>included 20 chicks exhibiting at least one extra-toe, pool <it>NA </it>included 20 non-polydactyly chicks showing the typical phenotype associated with heterozygosity for the naked neck mutation, and pool NP included 20 chicks exhibiting neither of the mutant phenotypes. Typings were done on an ABI-373 automatic sequencer with 147 microsatellite markers covering most of the genome. An unbalanced distribution of sire marker alleles were detected between pool <it>PO</it>, and pools <it>NA </it>and <it>NP</it>, for two markers of chromosome 2p, MCW0082 and MCW0247. A linkage analysis taking into account the incomplete penetrance of polydactyly (80%) was performed with additional markers of this region and showed that the closest marker to the <it>PO </it>locus was MCW0071 (5 cM, lod score = 9). MCW0071 lies within the engrailed gene <it>EN</it>2 in the chicken. In the mouse, the homologous gene maps on chromosome 5, close to the hemimelic extra-toes mutation <it>Hx</it>. In the case of the NA locus, markers of chromosome 3 were selected because <it>CPPP </it>was mapped on this chromosome. Analysis of individual typings showed a linkage of 5.7 cM (lod score = 13) between the NA locus and ADL0237 in the distal region of chromosome 3q. These results contribute to connecting the former classical map to the molecular genetic map of the chicken, and open the way to the identification of the molecular nature of two developmental mutations of the chicken that are known to occur in many breeds of chickens.</p>