Unequal crossing over during meiosis causes the chromosome missing some genes |
| Chromosomal mutations resulting in doubling of a part of a chromosome |
| An inverted chromosomal segment fractured from a chromosome is inserted at the newly created sticky ends of the same chromosome. |
| Breaks at the extreme ends of the short arms of two nonhomologousacrocentric chromosomes, and the small fragments produced are lost but the larger ones fuse together at their centromeric regions |
| Turner syndrome (45X0) and Klinefeltersyndrome (XXY) |
. | 95% of Down syndrome cases |
| Angelman syndrome |
| 3-4% of Down syndrome cases |