Distorted segregation resulting from pea chromosome reconstructions with alien segments from Pisum fulvum

Pea (Pisum sativum L.) satellited chromosome reconstructions were analyzed by cytologic markers to identify segregation distortion events, The presenc e of modified chromosomes was evaluated on the basis of additional rDNA gen es, an extra and a longer satellite, all derived from chromosome 5 and chro mosome 7 from P. fulvum Sibth, & Sm, The segregation of modified satellited chromosome 5 was monitored through fluorescent in situ hybridization with rDNA probe; it fitted the expected 1:2:1 ratio after self-pollination of a heterozygous genotype for modified chromosome 5, In different genotypes, wh ich were heterozygous for both modified chromosomes 5 and 7, the combined s egregation of these chromosomes showed the occurrence of seven karyotype cl asses instead of the expected nine, The classes with modified chromosome 7 and without modified chromosome 5, whether heterozygous or homozygous, were absent. The hypothesis of gamete selection was rejected since the expected segregation ratio of 5:3:1 was significant by chi-square test. Based on th e other hypothesis of postzygotic selection, the segregation ratio did not show a significant deviation from the expected 9:3:1 ratio, thereby indicat ing that embryo abortion caused the segregation distortion (SD), The hypoth esis of the SD system involving two loci carried by the alien satellites of modified chromosomes 5 and 7 is discussed in relation to the evolution of the P, fulvum genome.