Cytogenetical Evidence for Latent Centromeres and Reactivation in Chromosomes of Haplopappus gracilis (Asteraceae)

Abstract

Summary Rearranged karyotypes of 2nϭ5 present in three plants of Haplopappus gracilis (2nϭ4) were cytogenetically analyzed to clarify the origin of an additional centromere in the chromosome complement. One of the plants was a progeny of the homozygote with normal chromosome 1 crossed with the heterozygote with normal and centromere-shifted chromosome 1. The other two plants were derived from seedlings irradiated with X-rays during early germination stage. The chromosome complement of 2nϭ5 found in the first plant was comprised of 3 normal chromosomes (one chromosome 1 and two chromosome 2) and two rearranged chromosomes each possessing a centromere at the subterminal position. All the chromosome complements of the irradiated plants were similar to each other and each consisted of three normal chromosomes (one chromosome 1 and two chromosome 2) and 2 rearranged chromosomes, one large and metacentric and the other, fragmentlike. The origin of the additional centromere in each complement of 2nϭ5 is discussed from the point of chromosomal evolution in the genus Haplopappus.