Multiple Choice
You would be ,unlikely to see which of the following human cells dividing?
3. Energy & Cell Processes
Review of the Cell Cycle
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Down syndrome is characterized by cells having three copies of chromosome 21. As a cell in an individual with Down syndrome prepares to enter mitosis, how many chromatids would be present?
A
23
B
46
C
92
D
98
E
94
Verified step by step guidance1
Understand that Down syndrome is a genetic condition where there is an extra copy of chromosome 21, resulting in three copies instead of the usual two.
Recall that during the S phase of the cell cycle, each chromosome is replicated, resulting in two sister chromatids per chromosome.
Calculate the total number of chromatids for a typical human cell: Normally, humans have 46 chromosomes, which replicate to form 92 chromatids (46 chromosomes x 2 chromatids each).
Account for the extra chromosome 21 in Down syndrome: There are three copies of chromosome 21, so after replication, there will be 6 chromatids for chromosome 21 (3 chromosomes x 2 chromatids each).
Add the chromatids from the extra chromosome 21 to the typical number: 92 chromatids (normal) + 2 extra chromatids (from the third chromosome 21) = 94 chromatids in total.
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