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What is Down.s syndrome ? Give its sympt...

What is Down.s syndrome ? Give its symptoms and cause. Why is it that the chances of having a child with Down.s syndrome increases if the age of the mother exceeds forty years ?

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Down.s syndrome is a human genetic disorder caused due to trisomy of chromosome no. 21. Such individuals are aneuploid and have 47 chromosomes (2n + 1). The symptoms include mental retardation, growth abnormalities, constantly open mouth, dwarfness etc. The reason for the disorder is the non-disjunction (failure to separate) of homologous chromosome of pair 21 during meiotic division in the ovum. The chances of having a child with Down.s syndrome increase with the age of the mother (+40) because ova are present in females. Since their birth and therefore older cells are more prone to chromosomal non-disjunction because of various physico-chemical exposures during the mother.s life-time.
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