A new property of the maize B chromosome.
TB-9Sb is a translocation between the B chromosome and chromosome 9 in maize. Certain deletions of B chromatin from the translocation cause a sharp decrease in B-9 transmission compared to the rate for standard TB-9Sb. The deletions remove components of a B chromosome genetic system that serves to suppress meiotic loss in the female. At least two distinct B-chromosome regions suppress meiotic loss: one on the B-9 and one on 9-B. The system operates by stabilizing univalent B-type chromosomes. It allows the univalents to migrate to one pole in meiosis, despite the absence of a pairing partner. The findings reported here are the first evidence for genetic control of meiotic loss by a B chromosome. However, it is proposed that the practice of suppressing meiotic loss is common to the B chromosomes of all species. The need to suppress meiotic loss results from the fact that B chromosomes are frequently unpaired in meiosis and subject to very high frequencies of loss. B chromosomes may utilize one or more of the following methods to suppress meiotic loss: (a) regular migration of univalent B's to one pole in meiosis, (b) enhanced recombination between B chromosomes and (c) mitotic nondisjunction.
Carlson
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Botany Department, University of Iowa, Iowa City 52242.
Roseman
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D000705:Anaphase; D002875:Chromosomes / Q000648:ultrastructure; D003434:Crossing Over, Genetic; D008540:Meiosis; D008677:Metaphase; D008938:Mitosis; D014178:Translocation, Genetic; D003313:Zea mays / Q000166:cytology / Q000235:genetics*