GENETIC-MAPPING OF DNA SEGMENTS RELATIVE TO THE LOCUS FOR THE FRAGILE-X SYNDROME AT XQ27.3

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 37  (3) , 463-472
Abstract
Linkage was tested between the locus for the [human] fragile-X [fra(X)] syndrome at Xq27.3 and 5 polymorphic restriction sites identified by 4 DNA probes mapping distal to Xq26.1. A maximum distance of .apprx. 15 centimorgans (cM) between Xq27.3 and the marker loci mapping to this region was predicted based on the physical chromosome length. Close linkage between the disease and marker loci was excluded for probes DXS19 and DXS37 (.theta. = 0.05, Z = -2.94 and Z = -4.17, respectively). These marker loci were estimated to be less than 5 cM apart but .apprx. 40 cM proximal to the fragile site, indicating that there is a significantly greater frequency of recombination in this region of the X chromosome than expected from the physical length. Linkage results for the other marker loci and the fra(X) syndrome were inconclusive. The pX45d probe locus appears very closely linked to the factor IX locus (Z = 1.94 at .theta. = 0) and is .apprx. 20 cM proximal to Xq27.3. A relative map of the polymorphic restriction sites, fra(X) syndrome locus, and factor IX locus was constructed by maximizing lod scores over the Xq26.1 .fwdarw. q27.3 region.