Advertisements
Advertisements
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
Advertisements
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.
APPEARS IN
संबंधित प्रश्न
What is the average cell cycle span for a mammalian cell?
Distinguish cytokinesis from karyokinesis.
Describe the events taking place during interphase.
What is G0 (quiescent phase) of cell cycle?
Why is mitosis called equational division?
Name the phase of the cell cycle at which the following event occurs:
Crossing over between homologous chromosomes takes place.
Most cytogenic activities occur during
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?
Mitosis is characterised by ______.
Which tissue of animals and plants exhibits meiosis?
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?
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?
Comment on the statement – Telophase is reverse of prophase.
Name the phase of the cell cycle at which the following event occurs:
Centromere splits and chromatids separate.
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:
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:
