In an inversion heterozygote. one of its chromosomes shows the following linkage relationship:
In the homologous chromosome, there exists an inversion in the region
(1)What type of inversion is it
(2)Please draw a synaptic scheme(联会图)of these two chromosomes.
(3)If in the inverted chromosome region there is a lethal gene D at d locus, and in the normal(i.e., without inversion)chromosome there is another lethal gene F at f locus. How much of F1 individuals will be double(both at d and f loci) heterozygote when the inversion heterozygote self-crosses Why
参考答案：(1)臂内倒位(paracentric inversion)。
(2)这两条染色体的联会图(synaptic scheme)是：
(3)几乎100%为双重杂合子(double heterozygote)。因为倒位导致显著的遗传学效应——交换抑制(crossover repressing)。对于臂内倒位来说，倒位环内非姐妹染色单体间的单交换产物要么有两个着丝粒，要么没有着丝粒。含有这样的重复或缺失的配子不育。当分别位于两个同源染色体上的两个致死基因(lethal genes)处于倒位杂合子的倒位环内时，由于交换抑制、纯合个体致死，双重杂合子得以长期保存(平衡致死系统，balanced lethal system)。