OBJECTIVE LIFE SCIENCE
CELL BIOLOGY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Down syndrome occurs when an individual has three on chromosome 21. Which best explains the cause of Down Syndrome?
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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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Explanation:
Detailed explanation-1: -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-2: -Researchers believe that having extra copies of genes on chromosome 21 disrupts the course of normal development, causing the characteristic features of Down syndrome and the increased risk of health problems associated with this condition.
Detailed explanation-3: -If homologous chromosomes fail to separate during meiosis I, the result is two gametes that lack that chromosome and two gametes with two copies of the chromosome.
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