Skewed RAPD markers in linkage maps of Citrus

The objective of this work was to analyze the effects of RAPD markers with skewed segregation on genetic linkage maps. Segregation data for 123 Citrus sinensis (L.) Osbeck cv. Pêra markers and 53 C. reticulata Blanco cv. Cravo markers in F1 progeny composed of 94 hybrids were used. Genetic linkage maps of the two varieties were constructed with non-skewed markers (p < 0.05 and p < 0.01) using the program MAPMAKER 3.0 and a pseudo-testcross strategy. The maps were compared to those constructed with all markers. Alterations in the genetic distances were observed based on the location of the skewed markers within the linkage groups. Generally, the skewed markers were located at the end of the linkage groups, sometimes forming entire linkage groups, without causing significant distance modifications. However, skewed markers located between non-skewed markers caused significant distance modifications and, in some cases, altered the order of the markers. Most of the skewed markers can be included in linkage maps, but in each case the degree of distance modification caused by each marker needs to be assessed.