Linkage analysis of canine dewclaw locus

Abstract

The canine species including wolf and jackal usually have 4 digits on their hind limb. Rarely, however, there is an abnormal $1^st$ digit, which is named dewclaw and believed to be genetically transmittable. This preaxial polydactyly was first reported in 1947. Since then, a number of investigations have been made on the phenotype and symptom of dewclaw. However, dewclaw locus is not determined yet. The purpose of the present investigation is to find a dewclaw locus via genome-wide scanning. To this end, we first took 7 pedigrees which comprise 66 individuals. Analyzing 206 microsatellites under both autosomal-dominant and autosomal-recessive conditions, we found a highly significant linkage of dewclaw to the marker AHT131 on the canine chromosome (CFA) 16 only in autosomal-dominant mode. For identification of the locus of dewclaw, we increased the number of the pedigree to study from 7 to 9 with 135 individuals. Genotyping of 19 markers on CFA16 with ~ 4 cM interval gave two-point logarithm-of-odds (LOD) scores greater than 1. The maximum LOD score for the nine-family analysis was 20.76 at a recombination fraction (θ) of 0.000 for the chromosome 16 marker REN85M08/REN85N14. Other remarkable LOD score were 18.31 at θ =0 for the CFA 16 marker REN176D05, and 9.85 at θ =0 for the maker AHT131. On the basis of the recombination events in the families, a candidate region of 13 cM was defined by the UCMCF12 and CXX876 markers. In addition, previous CFA 16 linkage maps were reevaluated and a new map was proposed. The present investigation on CFA16 should provide us with further understanding of digit formation not only in the dog but also in the human since CFA16 was previously reported to be syntenic to the human chromosome 7q, 8p, and 4p where various genes associated with limb development are located.