Question :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 ?

Question :What is Down.s syndrome ? Give its symptoms and cause. Why i

1.	Question :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 ?
Answer» Solution : 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.