The arrangement of Pisum chromosomes in interphase

Abstract

Root tip cells of Pisum sativum were analyzed for the position of two chromosomes (4 and 7) that carry the nucleolar organizing region. Because of a characteristic heterochromatic pattern of these chromosomes, they can be identified in interphase. The positions of these regions were measured in relation to the center of the nucleus and to one another. The values were statistically evaluated by means of multiple tests of significance. The results discussed show clearly that in P. sativum cells the distribution of the nucleolar organizing chromosomes is not random and that the chromosomes analysed occupy special sites. There was no evidence that homologous chromosomes are more adjacent than heterologous ones, nor that morphologically similar chromosomes are neighbours. The present investigations have also shown that the position of the chromosomes is altered if the structure of the chromosomes is changed by reciprocal translocations.Key words: chromosome position, somatic pairing, translocation, heterochromatin, C-banding, multiple tests of significance.