Chiasmata and a Spontaneous Translocation Heterozygote in a Natural Population Involving the B-Chromosome of Lilium japonicum

Abstract

1. Among eight plants of Lilium japonicum sampled from a natural habitat, seven were normal, with 12_II+0-4B's: mean number of small telocentric B-chromosomes was 1.86 per plant. Homologous two B's paired frequently with each other but not with ordinary chromosomes. From 1 to 7 chiasmata were formed at random with mean frequency of 3.44 per bivalent at MI. No remarkable difference between the plants with and without B's was found. Spontaneous aberrations such as altered bivalent with chromosome breakage and sister reunion, bridge and fragment, loop and fragment, bridge, acentric fragment, and trisomics were recorded with low frequency at MI and AI.
2. The remaining one plant was heterozygote for translocation, 1_IV+10_II, which is characterized by absence of ring-of-four multiple. The constant formation of 1 to 2 chiasmata was observed on both interstitital segments between kinetochore and break-point, the mean frequencies being 1.48 and 1.32 respectively for the segments. The relatively high frequency of interstitial chiasma should cause a reduction of fertility which makes the heterozygote disadvantageous for selection.