CELL STRUCTURES AND FUNCTION
CELL DIVISION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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DNA synthesis occurs
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The DNA in the nucleus is replicated
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Each chromosome multiplies into two identical chromosomes known as sister chromatids. Both chromatids contain the same copy of the DNA molecule.
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Both chromatids are joined at thecentromeres.
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stage, the nucleus looks big
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Detailed explanation-1: -In the S phase (synthesis phase), DNA replication results in the formation of two identical copies of each chromosome-sister chromatids-that are firmly attached at the centromere region. At this stage, each chromosome is made of two sister chromatids and is a duplicated chromosome.
Detailed explanation-2: -The two “sister” chromatids are joined at a constricted region of the chromosome called the centromere. During cell division, spindle fibers attach to the centromere and pull each of the sister chromatids to opposite sides of the cell. Soon after, the cell divides in two, resulting in daughter cells with identical DNA.
Detailed explanation-3: -Centromere Identity Is Preserved During Cell Division During the S phase that follows mitotic division, the presence of CENP-A nucleosomes marks the position of the centromere on the two daughter DNA strands.
Detailed explanation-4: -During DNA replication/S phase, replication of centromere-DNA results in the distribution of CENP-A onto the two nascent DNA strands. This causes a twofold reduction in CENP-A at each centromere-DNA sequence (red to pink chromatin) (see Fig.
Detailed explanation-5: -During S phase, each chromosome is replicated. This produces a second copy of each chromosome from the mother and a second copy of each chromosome from the father. These identical copies are known as sister chromatids. These sister chromatids are held together by the centromere.