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Three copies of chromosome-21 in a child...

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 onchromosome-2 1. 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-l

B

Maternal meiosis-l

C

Paternal meiosis-ll

D

Maternal meiosis-ll

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