OBJECTIVE LIFE SCIENCE
MOLECULAR BIOLOGY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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substitution during mitosis
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frameshift mutation during mitosis
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translocation during meiosis
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nondisjunction during meiosis
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Detailed explanation-1: -Down syndrome is caused by a random error in cell division that results in the presence of an extra copy of chromosome 21 . The type of error is called nondisjunction (pronounced non-dis-JUHNGK-shuhn).
Detailed explanation-2: -Trisomy 21 or Down syndrome (DS) is one of the most common chromosomal abnormalities. The majority of full trisomy 21 is caused by chromosomal nondisjunction occurring during maternal meiotic division (∼90%).
Detailed explanation-3: -Mitotic nondisjunction can occur due to the inactivation of either topoisomerase II, condensin, or separase. This will result in 2 aneuploid daughter cells, one with 47 chromosomes (2n+1) and the other with 45 chromosomes (2n-1). Nondisjunction in meiosis I occurs when the tetrads fail to separate during anaphase I.