OBJECTIVE LIFE SCIENCE
GENETICS
Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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True
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False
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Either A or B
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None of the above
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Detailed explanation-1: -The overwhelming majority of trisomy 21, or Down syndrome, is caused by the failure of chromosomes to separate properly during meiosis, also known as chromosome nondisjunction.
Detailed explanation-2: -Patients with Down syndrome have an extra copy of their 21st chromosome. This extra chromosome is usually acquired before fertilization in meiosis, which is the process where sperm and egg cells, or gametes, are made.
Detailed explanation-3: -Nondisjunction can occur during either meiosis I or II, with differing results. If homologous chromosomes fail to separate during meiosis I, the result is two gametes that lack that particular chromosome and two gametes with two copies of the chromosome.
Detailed explanation-4: -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).