CELL DIVISION
THE CELL CYCLE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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During crossing over, DNA strands become tangled leading to three-stranded DNA
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During DNA replication, a chromosome is incorrectly replicated one additional time
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During meiosis, either homologous chromosomes or sister chromatids fail to separate
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During mitosis, either homologous chromosomes or sister chromatids fail to separate
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Detailed explanation-1: -Trisomy 21 (Nondisjunction) Down syndrome is usually caused by an error in cell division called “nondisjunction.” Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate.
Detailed explanation-2: -In translocation, a piece of chromosome or a whole chromosome breaks off during meiosis and attaches itself to another chromosome. The presence of an extra part of the number 21 chromosome causes the features of Down syndrome.
Detailed explanation-3: -Trisomy 21: About 95% of people with Down syndrome have Trisomy 21. With this type of Down syndrome, each cell in the body has 3 separate copies of chromosome 21 instead of the usual 2 copies.
Detailed explanation-4: -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%).