Department of Entomology, Virginia Polytechnic Institute and State University, 24061, Blacksburg, VA, USA.
Theor Appl Genet. 1984 Jan;67(2-3):123-9. doi: 10.1007/BF00317016.
A stock of Blattella germanica bearing the interchange T(3; 12)/3;12 was subjected to close inbreeding with selection for random disjunction at metaphase I. After 3-4 generations of selection, interchange quadrivalent chiasma frequency decreased, variability in free bivalent chiasma frequency increased sharply, and individuals with either random or directed disjunction were present in the stock. Random disjunction was modified from a ratio of 2∶1∶1∶2 (adj.-1; alt.-1; adj.-2; alt.-2) to a ratio of 1∶1∶1∶1. After 7-8 generations of selection, chiasma frequency appeared to stabilize at lower than normal levels and variability decreased for both quadrivalents and free bivalents. Directed disjunction was modified from a ratio of 2∶1∶1∶4 to 1∶1∶1∶2, and no individuals with the original high level of directed disjunction were detected. Chains-of-four tended to orient randomly, especially in individuals where the ring quadrivalents showed directed disjunction. Relaxation of inbreeding, but not selection, produced an increase in chiasma frequency and variability in both free bivalents and quadrivalents, but the modified ratios for both random and directed disjunction were retained. These results are discussed with respect to inbreeding effects and genetic control of chiasma frequency and metaphase I disjunction in interchange quadrivalents.
一批带有 T(3;12)/3;12 易位的德国小蠊经近交和着丝粒区Ⅰ期随机分离选择，经过 3-4 代的选择后，易位四价体交叉频率降低，自由二价体交叉频率的变异性急剧增加，并且在群体中出现了随机或定向分离的个体。随机分离从 2∶1∶1∶2 的比例（adj.-1; alt.-1; adj.-2; alt.-2）改变为 1∶1∶1∶1 的比例。经过 7-8 代的选择后，交叉频率似乎稳定在较低水平，四价体和自由二价体的变异性都降低。定向分离从 2∶1∶1∶4 的比例改变为 1∶1∶1∶2，并且没有检测到具有原始高水平定向分离的个体。四联体链倾向于随机定向，尤其是在显示定向分离的环状四价体中。尽管放松了近交，但选择并没有增加自由二价体和四价体的交叉频率和变异性，但保留了随机和定向分离的修改比例。这些结果与近交效应以及易位四价体着丝粒区Ⅰ期分离的交叉频率和遗传控制有关。
