18
Question
Three copies of chromosome 21 in a child with Downs 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 three copies two 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?
Three copies of chromosome 21 in a child with Downs 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 three copies two 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?
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Solution
The correct option is D Maternal meiosis - I
- Down's syndrome is mainly caused due to an extra copy of chromosome 21.
- The extra copy is formed due to non-disjunction of chromosomes during meiosis.
- In this case, as the two chromosomes of the child has the same allele as the mother so it can be concluded that the non-disjunction has taken place during maternal meiosis with duplication of maternal allele.
- So, the correct answer is option A.
- Down's syndrome is mainly caused due to an extra copy of chromosome 21.
- The extra copy is formed due to non-disjunction of chromosomes during meiosis.
- In this case, as the two chromosomes of the child has the same allele as the mother so it can be concluded that the non-disjunction has taken place during maternal meiosis with duplication of maternal allele.
- So, the correct answer is option A.
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