Question

Explain how nondisjunction generates aneuploidy. Describe the most common aneuploidy conditions. Given what you know about the X and Y chromosomes, why does YO not exist?

Answer 1

Nondisjunction means failure of the homologous chromosomes to separate during the process of meiosis. Sometimes it also occurs due to other reasons like failure of sister chromatids to separate from each in later phases of meiosis or even mitosis. So this results in abnormal increament in the number of chromosomes in a cell. Consider it this way , that when meiosis takes place properly there are 23 chromosomes per cell and when non disjunction occurs, the chromosomes that are bond togetehr for gene exchange are unable to deattach from each other causing abnormal number of chromosome per cell after the cell division occurs. So this presence of abnormal chromosomes which may be onw less or more than normal is aneuploidy and is caused majorly due to aneuploidy. The most common aneuploidy conditions are - Trisomy and Monosomy Trisomy occura in dieseases like Down syndrome and Edwards syndrome . YO does not exist because O means lack of X chromosome. But this is not possible in humans because they have only two sex chromosomes that are X and Y chromosome and Y chromosome determines the geneder. So absence of X chromosome is not possible because such type of chromosomal matching does not happen in humans. It could be absence of X completely but not like we are replacing the absence of X with O . YO is never inherited during gamete formation.

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