Practice question

Centromere mapping depends on ability to tell whether locus segregated at meiosis I reductional division or meiosis II equational division, which demands ordered arrangement where chromatid positions reflect spindle history accurately. In Neurospora linear octads, FDS blocks indicate no gene-centromere crossover preserving linkage, SDS alternating patterns indicate crossover between gene and centromere region. Unordered tetrads in yeast randomize spore positions erasing division timing information, so distinction impossible and gene-centromere distance immeasurable. Thus centromere distance measurement formula using half SDS percentage can only be applied to ordered tetrads, making Neurospora unique tool for centromere linkage studies.