Meiotic nondisjunction of chromosome 21 is a common reason in case of Down syndrome. This susceptibility to nondisjunction is found to be increased in women older than 45 years of age.
Hello Sourav Melekar
This is because of errors in meiosis that may be more likely to happen as a result of the aging process. One explanation for why meiotic segregation errors are more prevalent in older women is that cohesion between sister chromatids deteriorates with age and renders recombinant chromosomes susceptible to mis segregation.
Accurate segregation during meiosis I requires that homologous chromosomes undergo recombination and remain physically attached to one another until they segregate to opposite poles during anaphase I. In the absence of a stable connection, homologues will segregate randomly resulting in meiosis I nondisjunction. Cohesion between the arms of sister chromatids provides an evolutionarily conserved mechanism for maintaining the association of recombinant homologues. Normally, the release of arm cohesion at anaphase I allows recombinant homologues to segregrate to opposite poles. In the absence of cohesion, chiasmata are not maintained and homologous chromosomes mis segregate during meiosis I.
You may want to refer to the paper attached below for more information.
Article Aging Predisposes Oocytes to Meiotic Nondisjunction When the...
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The increased susceptibility to meiotic nondisjunction in older women is primarily attributed to the aging process affecting oocytes (egg cells). As women age, the quality of their eggs tends to decline due to various factors, such as an accumulation of genetic and environmental damage.During meiosis, the cell division process that produces eggs, chromosomes need to separate correctly to ensure each egg receives the right number of chromosomes. Meiotic nondisjunction occurs when chromosomes fail to separate properly, leading to an abnormal distribution of chromosomes in the resulting eggs.In older women, the risk of meiotic nondisjunction rises because the cellular machinery involved in maintaining chromosome segregation may become less efficient over time. This can result in an increased likelihood of errors during the division of egg cells, leading to a higher incidence of chromosomal abnormalities, such as Down syndrome, in offspring born to older mothers.
The harmony between the sister chromatids becomes more vulnerable with age that make the misaggregation between the chromosomes more likely. Also spindle abnormalities with faulty chromosome transformation in metaphase play an important role.
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