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CET Karnataka Medical CET - Karnataka Medical Solved Paper-2015

  • question_answer
    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 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

    Correct Answer: B

    Solution :

    : Downs syndrome is an autosomal aneuploidy, caused by the presence of an extra chromosome number 21. Both the chromosomes of the pair 21 pass into a single egg due to non-disjunction during oogenesis. The non-disjunction is more common in females. The frequency of non- disjunction of chromosome pair 21 increases with mothers age. Usually non-disjunction of chromosomes takes place in meiosis-I.


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