Half-disjunction in an Association of Four Chromosomes in Pisum sativum
Abstract
(John In/us Horticultural Institution, London.') With seven Figures in the Text. i. INTRODUCTION. HE occurrence of an interchange of segments between non-homologous chromosomes in plants was first suggested by Belling (2) as an explanation of partial sterility previously recorded by him in Stizolobiunt (1). The hypothesis has since proved adequate in interpreting further observations on other plants. ⢠If two non-homologous chromosomes made up of segments AB and CD respectively exchange segments B and D, the resulting chromosomes will be AD and BC respectively. In a plant in which-there are two normal chromosomes whose homologues have exchanged segments in this way (an interchange heterozygote) the interchanged chromosome AD will be able at meiosis to form chiasmata in segment A with segment A of AB, and in segment D with segment D of CD. Similarly the two segments of BC will be able to form chiasmata with the corresponding segments in AB and CD. An association of four chromosomes can therefore be formed, and such associations replacing two bivalents have been found in Datura hybrids (3,4), in Zea (5, 6, 16) in Campanula (11), and in Pisum (12-15, 17). In addition, associations of three and five chromosomes have been