In order to analyze the mapping data for loci on chromosome 6S in the cross (NK1 x NK2wx) x NK1, a SAS program was written which makes pairwise probe pattern comparisons. The number of differences between pairs of loci (including double crossovers) are shown in a "relatedness" triangle (Figure 1). The distance between loci was calculated (to the nearest 0.1 cM) using the number of probe differences. A map of chromosome 6S is shown in Figure 2. Comparison of this map with the 6S map from the 1988 MNL suggests that: 1) different mapping methods result in different relative amounts of recombination or 2) there is a parental line effect in the various mapping populations.
To examine these possibilities further, a number of probes on chromosome 3 and chromosome 9 were analyzed in the (NK1 x NK2wx) x NK1 BC 1 population and compared with the 1988 MNL maps (Figure 3a and b). The mapped distances differ significantly in the (NK1 x NK2wx) x NK1 population from those observed in the 1988 MNL maps. In this BC1 population the markers M81 and 5.10 are not linked to wx or 8.17. The presence of other numerous mapping differences makes it difficult to ascertain whether parental or test population differences are responsible for the discrepancies.
The reason for examining the BC1 population
was to map chromosome 6S markers as a prelude to incorporating the morphological
markers into the RFLP map. A number of crosses will be made in an attempt
to localize various morphological markers on the RFLP map.
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