Division of Biological Sciences, University of Missouri, Columbia, Missouri 65201.
Genetics. 1974 May;77(1):45-54. doi: 10.1093/genetics/77.1.45.
Enhancement of recombination by B chromosomes is influenced by the kind of heterochromatic knob present in or near the tested region of the A chromosomes. In homomorphic chromosome 9 bivalents of K(s)/K(s) constitution, double exchanges were increased at the expense of singles, but in the K*/K(s) 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.
B 染色体的重组增强受 A 染色体测试区域内或附近存在的异染色质节的影响。在同形 9 号染色体二价体中，K(s)/K(s)组成的双交换增加了，而在 K*/K(s)异型体中，单交换和双交换都增加了，无交换四分体减少了。只有在大孢子母细胞中观察到不同的 B 染色体节化合物对 B 染色体增强的修饰。在具有奇数和偶数 B 染色体的植物中发现了不同的重组频率；这种效应在大孢子母细胞中尤为明显。奇数或偶数 B 染色体产生的重组修饰是特定区域与节组成相互作用的结果。奇数 B 染色体比偶数 B 染色体更有效地增加重组。结论是，异染色质节和基本上是异染色质的多余染色体可能在交叉过程中相互作用，重组水平部分取决于节的组成。
