B-CHROMOSOME-STIMULATED CROSSING OVER IN MAIZE

George P Hanson

doi:10.1093/genetics/63.3.601

A stably transmitted pair of translocated supernumerary chromosomes in maize

Genome ◽

10.1139/g95-072 ◽

1995 ◽

Vol 38 (3) ◽

pp. 558-565 ◽

Cited By ~ 1

Author(s):

Marjorie P. Maguire

Keyword(s):

Chiasma Formation ◽

B Chromosome ◽

Supernumerary Chromosome ◽

Chromosome Segment ◽

Crossing Over ◽

Preferential Pairing ◽

Supernumerary Chromosomes ◽

Unknown Source ◽

Chromosome Segments

A pair of stably transmitted supernumerary chromosomes of unknown source has been found in a maize stock carrying a desynaptic mutant. The presence of the supernumerary chromosome appears to be unrelated to the meiotic mutant, but is believed to have been derived from a translocated B chromosome contaminant. The supernumerary chromosomes carry a segment of a A chromosome in this stock where there appear to be two normal copies of each of the 10 A chromosomes. Thus, this A chromosome segment is present in quadruplicate. Surprisingly, a quadrivalent configuration is formed in most microsporocytes, which involves not only synapsis but also chiasma formation in the A chromosome segments involved in the quadrivalent. This represents a strong preferential pairing of supernumeraries with the normal A chromosome segments. Such nonrandom association and crossing over might provide information on the nature of early homologue alignment at meiosis.Key words: supernumerary chromosomes, modified B chromosome, BA translocation, preferential pairing and crossing over.

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THE INTERACTION OF KNOBS AND B CHROMOSOMES OF MAIZE IN DETERMINING THE LEVEL OF RECOMBINATION

Genetics ◽

10.1093/genetics/77.1.45 ◽

1974 ◽

Vol 77 (1) ◽

pp. 45-54

Author(s):

C C Chang ◽

Gary Y Kikudome

Keyword(s):

B Chromosome ◽

B Chromosomes ◽

Chromosome 9 ◽

Crossing Over

ABSTRACT Enhancement of recombination by B chromosomes is influenced by the kind of heterochromatic knob present in or near the tested region of the A chramosomes. In homomorphic chromosome 9 bivalents of KS/KS constitution, double exchanges were increased at the expense of singles, but in the K*/Ks heteromorphs there was a gain in both single and double exchanges at the expense of no-exchange tetrads. Modification of the B chromosome enhancement in different knob compounds was observed only in the megasporocytes.—Different frequencies of recombination are found in plants with odd and even numbers of B Chromosomes; this effect is especially striking in the megasporocytes. The modification in recombination produced by an odd or even number of B chromosomes is a function of the interaction of a particular region and the knob constitution. Odd numbers of B chromosomes were more effective than even numbers in causing increased recombination.—It is concluded that heterochromatic knobs and the essentially heterochromatic supernumeraries may interact in the process of crossing over, with the level of recombination determined in part by knob constitution.

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