Question

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. Maternal meiosis – I
• B. Maternal meiosis –II
• C. Paternal meiosis – I
• D. Paternal meiosis – II

Answer 1

The correct option is A

Maternal meiosis – I

Maternal meiosis – I