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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 the average cell cycle span for a mammalian cell?
Describe the events taking place during interphase.
Why is mitosis called equational division?
Cells in the quiescent stage (Go)
Name the stage of mitosis in which chromosomes are arranged on the equator of spindle:
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 ______
Which of the phases of cell cycle is of longest duration?
Which tissue of animals and plants exhibits meiosis?
Which part of the human body should one use to demonstrate stages in mitosis?
It is said that the one cycle of cell division in human cells (eukaryotic cells) takes 24 hours. Which phase of the cycle, do you think occupies the maximum part of cell cycle?
Label the diagram and also determine the stage at which this structure is visible.
While examining the mitotic stage in a tissue, one finds some cells with 16 chromosomes and some with 32 chromosomes. What possible reasons could you assign to this difference in chromosome number. Do you think cells with 16 chromosomes could have arisen from cells with 32 chromosomes or vice versa?
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
Comment on the statement – Telophase is reverse of prophase.
Name the phase of the cell cycle at which the following event occurs:
Pairing between homologous chromosomes takes place.
Spindle fibers attach to kinetochores of chromosomes during ______.
Match List I with List II:
| List I | List II |
| A. M Phase | I. Proteins are synthesised |
| B. G Phase | II. Inactive phase |
| C. Quiescent stage | III. Interval between mitosis and initiation of DNA replication |
| D. G, Phase | IV. Equational division |
Choose the correct answer from the options given below:
