Cytogenetic studies of three paracentric inversions in barley

Following treatments with neutrons, X‐rays and glycidol, three inversions in barley were isolated and designated NI 501, XI 501 and CI 501, respectively. The occurrence of an inverted segment in heterozygous condition caused the formation of different aberrant configurations during anaphase I and II in the PMC, leading to reduced pollen fertility. The seed set was usually reduced to the same extent as the pollen fertility. Fertility in NI 501 and CI 501 was more reduced than in XI 501. The effects of single and double crossing‐over occurring within and outside the inversion on the types of anaphase configuration are discussed. The gametic segregation in F 1 following various positions of marker genes and crossing‐over inside and outside the inversion is analysed. Results so far obtained from linkage tests suggest that NI 501 and CI 501 have a distal location close to br in the short arm of chromosome 1 whereas XI 501 is completely linked to trd in the long arm of chromosome 5. A review of methods for calculating linkage intensities is made. Formulas used for calculation of χ 2 values and maximum likelihood equations designed for three kinds of crosses involving inversions and marker genes are tabulated.