EMBRYOLOGY
CHROMOSOMES AND CELL DIVISIONS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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chromatides are pulled to opposite sides of cell
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chromosomes become visible as 2 stranded
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Chromosomes make a copy (DNA replication)
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Chromosomes disappear
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Detailed explanation-1: -DNA replication begins with the unwrapping and unwinding of the highly compacted chromatin structure. The two strands of the double helix must also be separated before the replication machinery can access and copy each strand.
Detailed explanation-2: -Before mitosis, the chromosomes are copied. They then coil up, and each chromosome looks like a letter X in the nucleus of the cell. The chromosomes now consist of two sister chromatids. Mitosis separates these chromatids, so that each new cell has a copy of every chromosome.
Detailed explanation-3: -The initiation of DNA replication occurs in two steps. First, a so-called initiator protein unwinds a short stretch of the DNA double helix. Then, a protein known as helicase attaches to and breaks apart the hydrogen bonds between the bases on the DNA strands, thereby pulling apart the two strands.
Detailed explanation-4: -When a cell divides, it is important that each daughter cell receives an identical copy of the DNA. This is accomplished by the process of DNA replication. The replication of DNA occurs during the synthesis phase, or S phase, of the cell cycle, before the cell enters mitosis or meiosis.