Chromosomes in meiosis-1 and chromatids in meiosis-2 do not separate normally, it is called non-disjunction. Non-disjunction results in either too many or too few chromosomes in the gamete. Cohesin protein increases the probability of non-disjunction in the egg. Genetic abnormalities in human babies due to non-disjunction are:
1. Patao syndrome: Patao syndrome is caused by trisomy on human chromosome 13.
2. Edward’s syndrome: Edward’s syndrome occurs when human trisomy occurs on chromosome 18. Dr. Siddique Publications
3. Down syndrome: Down syndrome occurs when trisomy occurs on human chromosome 21.
4. Klinefelter syndrome: Klinefelter syndrome occurs when the male zygote has an excess of X chromosomes. For example- XXY.
5. XYY syndrome: XYY syndrome occurs when a male zygote has an extra Y chromosome.
6. Turner syndrome: If there is less X chromosome in the female zygote, Turner syndrome occurs. Siddique Publications
7. Triple X Syndrome: Triple X syndrome occurs when there is an extra X chromosome in the female zygote. For example, XXX.