Practice question

In unordered tetrad collection from yeast or other fungus, linkage detection relies on comparing counts PD and NPD. Since PD requires no crossover and NPD requires double crossover involving all chromatids, linked loci favor PD over NPD markedly because single crossover insufficient to generate NPD. Statistical test evaluates whether PD significantly greater than NPD using chi-square or exact test. If equality holds, genes assort independently irrespective TT frequency. Significant excess PD provides evidence linkage even before map distance calculated. Once linkage confirmed, distance calculated weighting TT and NPD contributions appropriately.