Nondisjunction in meiosis I
Homologous chromosomes do not separate properly (all cells abnormal)
Nondisjunction in meiosis I refers to the failure of homologous chromosome pairs to separate properly during the first division of meiosis. This results in one daughter cell receiving an extra chromosome and the other receiving one less chromosome.
This can occur in several different ways. For example, all of the homologous chromosomes might remain attached to each other and move to one pole of the cell, leaving the other pole without any chromosomes of that type. Alternatively, one entire homologous pair might fail to separate, resulting in one daughter cell with two copies of that chromosome and the other with none.
Nondisjunction can lead to a variety of genetic disorders, including Down syndrome (caused by an extra copy of chromosome 21), Turner syndrome (caused by a single X chromosome in females), and Klinefelter syndrome (caused by an extra X chromosome in males). These genetic disorders can have a wide range of physical and intellectual effects, depending on the specific chromosomes affected and the severity of the non-disjunction event.
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