Carlson W R, Roseman R R
Botany Department, University of Iowa, Iowa City 52242.
Genetics. 1992 May;131(1):211-23. doi: 10.1093/genetics/131.1.211.
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.
TB-9Sb是玉米B染色体与9号染色体之间的易位。与标准TB-9Sb相比，该易位中B染色质的某些缺失导致B-9的传递率急剧下降。这些缺失去除了一个B染色体遗传系统的组成部分，该系统用于抑制雌性减数分裂过程中的丢失。至少有两个不同的B染色体区域抑制减数分裂丢失：一个在B-9上，另一个在9-B上。该系统通过稳定单价B型染色体来运作。它允许单价染色体在减数分裂中迁移到一极，尽管没有配对的同源染色体。本文报道的研究结果是B染色体对减数分裂丢失进行遗传控制的首个证据。然而，有人提出抑制减数分裂丢失的机制在所有物种的B染色体中普遍存在。抑制减数分裂丢失的需求源于B染色体在减数分裂中经常不配对且丢失频率非常高这一事实。B染色体可能利用以下一种或多种方法来抑制减数分裂丢失：（a）单价B染色体在减数分裂中常规迁移到一极，（b）B染色体之间重组增强，以及（c）有丝分裂不分离。
