Q. 3. What is Down's syndrome? Give its symptoms and cause. Why is it that the chances of having a child with Down's syndrome increase if the age of the mother exceeds forty years?
Down's syndrome is a human genetic disorder caused due to trisomy of chromosome number 21. Such individuals are aneuploid and have 41 chromosomes, i.e., (2n+1)
Symptoms of down's syndrome are
i. Mental retardation
ii. Growth abnormalities
iii. Constantly open mouth
iv. Dwarfness, etc., gonads and genitalia underdeveloped
The reason for the disorder is the non-disjunction (failure to separate) of the homologous chromosome (a pair 21 during the meiotic division. The chances of having a child with Down's syndrome increases with the age of the mother (+40) because age adversely affects meiotic chromosome non-disjunction.
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