Three copies of chromosome – 21 in a child with Down’s syndrome have been analysed using molecular biology technology to detect any possible DNA polymorphism with reference to different alleles located on chromosome – 21. Results showed that out of 3 copies 2 of the chromosomes of the child contain the same alleles as one of the mother’s alleles. Based on this when did the non-disjunction event most likely occur?
(a) Paternal meiosis-I
(b) Maternal meiosis-I
(c) Paternal meiosis-II
(d) Maternal meiosis-II
