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प्रश्न
Analyse the events during every stage of cell cycle and notice how the following two parameters change.
- Number of chromosomes (N) per cell
- Amount of DNA content (C) per cell
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उत्तर
During meiosis, the number of chromosomes and the amount of DNA in a cell change.
- Number of chromosomes (N) per cell
- The cell is metabolically active in the G1 phase of interphase. It continues to increase continuously. DNA replication occurs in the S phase.
- As a result, the amount of DNA doubles. If the initial amount of DNA is expressed as 2C, then its amount becomes 4C, while there is no change in the number of chromosomes.
- If the number of chromosomes in the G1 phase is 2N, then even in the G2 phase, their number remains 2N.
- Amount of DNA content (C) per cell
- During anaphase II of the meiotic cycle, the chromatids separate as a result of the splitting of the centromere.
- It is the centromere that holds together the sister chromatids of each chromosome. As a result, the chromatids move towards their respective poles.
- Therefore, at each pole, a haploid number of chromosomes and a haploid amount of DNA are present.
- During mitosis, the number of chromosomes remains the same.
- The DNA duplicated in the S phase gets separated in the two daughter cells during anaphase. As a result, the DNA content (C) of the two newly-formed daughter cells remains the same.
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संबंधित प्रश्न
What is G0 (quiescent phase) of cell cycle?
Name the phase of the cell cycle at which the following event occurs:
Crossing over between homologous chromosomes takes place.
Cells in the quiescent stage (Go)
Most cytogenic activities occur during
Match List - I with List - II.
| List I | List II | ||
| (a) | S phase | (i) | Proteins are synthesized |
| (b) | G2 phase | (ii) | Inactive phase |
| (c) | Quiescent stage | (iii) | Interval between mitosis and initiation of DNA replication |
| (d) | G1 phase | (iv) | DNA replication |
Choose the correct answer from the options given below.
The fruit fly has 8 chromosomes (2n) in each cell. During the interphase of Mitosis if the number of chromosomes in G1 phase is 8, what would be the number of chromosomes after the S phase?
The centriole undergoes duplication during ______
Cells which are not dividing are likely to be at ______.
Between a prokaryote and a eukaryote, which cell has a shorter cell division time?
Which of the phases of cell cycle is of longest duration?
Which part of the human body should one use to demonstrate stages in mitosis?
Mitosis results in producing two cells which are similar to each other. What would be the consequence if the following irregularities occur during mitosis?
Duplication of DNA does not occur
Two key events take place, during S phase in animal cells, DNA replication and duplication of centriole. In which parts of the cell do events occur?
Name the phase of the cell cycle at which the following event occurs:
Chromosomes are moved to spindle equator.
Name the phase of the cell cycle at which the following event occurs:
Pairing between homologous chromosomes takes place.
Statement I: During GO phase of cell cycle, the cell is metabolically inactive.
Statement II: The centrosome undergoes duplication during S phase of interphase.
In the light of the above statements, choose the most appropriate answer from the options given below:
