Further Studies of Asynaptic Maize

Abstract

Synapsis occurs, apparently normally, in asynaptic maize plants. Homologous chromosomes tend to separate during pachytene without chiasma formation. Chiasma frequency is low at diplotene, diakinesis and metaphase. The degree of metaphase pairing in asynaptic plants is variable. The plants studied showed the maximum possible range in modal frequency of number of bivalents, namely, from 0 to 10. There is a positive correlation between number of bivalents at metaphase and minimum number of chiasmata which must be assumed to account for the observed associations. The observations support Darlingtonâtms hypothesis of post-diplotene association of homologous chromosomes by chiasmata. In asynaptic sporocytes which show no metaphase pairing of chromosomes the spindle is considerably longer than in comparable normal sporocytes. This elongation of the spindle in asynaptic plants is probably related either to the lack of metaphase pairing or to the lack of orientation of chromosomes on the equatorial plate. Crossing over in asynaptic plants, as measured in the normal ten chromosome gametes, is approximately normal, presumably because such gametes make up a highly selected sample. The asynaptic gene is located in the P-br chromosome approximately midway between the P and br genes. © 1933, Japan Mendel Society, International Society of Cytology. All rights reserved.