1、Inv dup (15) 导致的声带发育不全、智障、发育迟缓、脊椎弯曲、孤独症,6.1.3 Inversions (倒位)Inversions turn part of the chromosome around, reversing its polarity. A chromosome with an inversion can pair with a normal chromosome in meiosis in a heterozygote and form an inversion loop.,倒位纯合体完全正常，不影响个体生活力。倒位杂合体同源配对形成倒位环 “inversion l
2、oop”， 倒位片段上的基因在连锁群中的排序也改变了。,Meiotic recombination within an inversion loop duplicates one end of each chromatid and deletes the other end in a reciprocal manner. These recombined chromatids are therefore not viable, and do not reach the next generation.,6.1.3.1 Paracentric inversions (臂内倒位）,j i h e
3、f g d c b a,Paracentric inversions (臂内倒位） These do not include the centromere. Meiotic recombination in a paracentric inversion loop generates a dicentric chromatid (two centromeres) and an acentric (no centromere) fragment. Most dipterans (true two-winged flies) can tolerate this because they have
4、no recombination in males so sperm all contain complete chromosomes, and female dipterans have mechanisms to ensure that only unrecombined chromatids reach the egg cell, so zygotes are viable.,臂内倒位（paracentric inversions） ：着丝粒在倒位环外，环内发生片段交换重组，减数分裂后期出现“桥”和“断片” 一条染色单体含双着丝粒，另一条无着丝粒,6.1.3.2 Pericentric
5、inversions (臂间倒位）,Pericentric inversions (臂间倒位）These invert the centromeric region. The effects of meiotic recombination in the loop duplicating and deleting the ends of the chromatid cannot be avoided because all chromatids have one centromere. Many zygotes will have unbalanced genomes. Pericentric
6、 inversions only persist as polymorphisms in species where they do not recombine at meiosis.,臂间倒位（pericentric inversions ）:着丝粒在倒位环內，环内发生交换重组，染色单体产生缺失或重复，形成不平衡配子，无生活力。,遗传效应：染色单体发生交换后产生缺失和重复的不育配子，存活的配子应是未发生交换重组的。倒位可以抑制和大大降低倒位环内的基因重组。,6.1.4 Translocations,易位是非同源染色体间的片段交换,Flash-Robertsonian双语课件中,纯合体易位没有
7、明显的细胞学特征，与未易位相似。杂合体易位体同源配对出现十字形图，随着着丝点趋向两极，成圆形或8字，各50%概率,倒“8”字 交替式不育 上下相邻可育,“O”型 交替式可育 相邻不育,Translocations involve exchange of distal regions of nonhomologous chromosomes. It is necessary that either both rearranged or both original chromosomes occur in the same gamete to ensure genetic balance. If
8、two adjacent chromosomes segregate to the same pole, genetically unbalanced gametes will be produced, but if alternated chromosomes go together, the gametes will contain a complete balanced genome. Some species are heterozygous for many translocations, and form long chains or rings of chromosomes in meiosis.,
