Chromosome Associations during Meiosis in Haploid Maize (Zea mays L.)

Study of meiotic behaviour of maize haploids revealed the presence of intrachromosomal duplications which are manifested by fold-back pairing of distal segments or of whole chromosomes. Interchromosomal duplications, though to a much lesser extent, were also suggested from the results. In a study of 350 cells at metaphase, associations were ten univalents in 63.43 percent, eight univalents and one bivalent in 31.14 percent, and six univalents and two bivalents in 3.72 percent cases. Tri and pentavalents were also observed in few cells.Most of the bivalent configurations in dia-metaphase were considered to be pseudo-associations resulting from apposition of heterochromatic segments of two heterologous chromosomes. Bivalent formation appeared to be non-specific, among different members of the complement, and there was also a preponderance of end-to-end associations. Bivalent associations were found to persist through late anaphase. Anaphase distribution was random and segregation of chromosomes to poles followed the expected pattern.It is suggested that modern maize is not an alloploid and the haploids studied represented true monoploids with intra and possibly interchromosomal duplications.