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Question
Down syndrome is due to non-disjunction of
Down syndrome is due to non-disjunction of
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Solution
The correct option is C Autosome
Down syndrome is trisomy 21, i.e., presence of chromosome 21 in three copies. Non-disjunction of a bivalent during meiosis produce gametes with "n+1 and n-1". Fertilization of n+1 gamete with a normal gamete produce 2n+1 individual. Hence, non-disjunction is the direct cause of Down syndrome. As we know that chromosomes other than sex chromosomes are called as autosomes; chromosome 21 is an autosome. Option C is the correct answer. The gene for Down syndrome is not present on X- or Y-chromosomes; nondisjunction of these chromosomes do not produce Down syndrome. It makes options A and B wrong. Down syndrome is the disorder of human, not of Drosophila; option D is wrong.
Down syndrome is trisomy 21, i.e., presence of chromosome 21 in three copies. Non-disjunction of a bivalent during meiosis produce gametes with "n+1 and n-1". Fertilization of n+1 gamete with a normal gamete produce 2n+1 individual. Hence, non-disjunction is the direct cause of Down syndrome. As we know that chromosomes other than sex chromosomes are called as autosomes; chromosome 21 is an autosome. Option C is the correct answer. The gene for Down syndrome is not present on X- or Y-chromosomes; nondisjunction of these chromosomes do not produce Down syndrome. It makes options A and B wrong. Down syndrome is the disorder of human, not of Drosophila; option D is wrong.
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