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

Solution:

The presence of an extra copy of chromosomal number 21 (9trisomy of 21) causes Down syndrome. 23 pairs of autosomes and 1 pair of sex chromosomes make up the karyotype. (There are a total of 24 pairs of chromosomes, or 47 chromosomes). Because ova are present in females since birth, and older cells are more prone to chromosomal non-disjunction, having a kid with Down’s syndrome increases if the mother’s age surpasses forty years.