Cell Cycle And Cell Division
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A cell at telophase stage is observed by a student in a plant brought from the field. He tells his teacher that this cell is not like other cells at telophase stage. there is no formation of cell plate and thus the cell is containing more number of chromosomes as compares to other dividing cells. This would result in
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polyploidy
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somaclonal variation
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polyteny
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aneuploidy
A.
polyploidy
Polyploid cells have a chromosome number that is more than double the haploid number.
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A somatic cell that has just completed the S phase of its cell cycle, as compared to gamete of the same species, has
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twice the number of chromosomes and four times the amount of DNA
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same number of chromosomes but twice the amount of DNA
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twice the number of chromosomes and four times the amount of DNA
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four times the number of chromosomes and twice the amount of DNA
C.
twice the number of chromosomes and four times the amount of DNA
In general a gamete contains 'n' number of chromosomes (haploid) and 'x' amount of DNA. In comparison to the gamete, an (diploid) somatic cell usually have 2n number of chromosomes and 2x amount of DNA. But, after the cell enters and complete the 'S'-phase of its cell cycle, the DNA content of the cell becomes double (due to its duplication). However, the number of chromosomes remains the same. Hence, the somatic cell that has undergone and completed its 'S' phase of cell cycle will have twice the number of chromosomes and four times the DNA content.
| Chromosomes | DNA content | |
| Gamete | n | x |
| Somatic cell (diploid) | 2n | 2x |
| Somatic cell (after S-phase) | 2n | 4x |
A stage in cell division is shown in the figure. Select the answer which gives correct identification of the stage with its characteristics
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Telophase
Nuclear envelope reforms, Golgi complex reforms
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Late anaphase
Chromosomes move away from equatorial plate, Golgi complex not present
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Cytokinesis
Cell plate formed, Mitochondria distributed between two daughter cells
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Telophase
Endoplasmic reticulum and nucleolus not reformed yet
A.
|
Telophase |
Nuclear envelope reforms, Golgi complex reforms |
Telophase is the reserve of prophase. The chromosome that has reached their respective polar decondense and their individually. Late anaphase is characterised by centromeres split and chromatid moves to opposite poles. Cytokinesis is processed in which cell itself is divided two daughter cells.
Anaphase promoting complex (APC) is a protein degradation machinery necessary for proper mitosis of animal cells. If APC is defective in a human cell, which of the following is expected to occur?
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Chromosomes will not condense
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Chromosomes will be fragmented
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Chromosomes will not segregate
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Recombination of chromosome arms will occur
C.
Chromosomes will not segregate
Anaphase Promoting Complex (APC) is a protein necessary for separation of daughter chromosomes during anaphase. If APC is defective then the chromosomes will fail to segregate during anaphase.
Arrange the following events of meiosis in correct sequence:
(a) Crossing over
(b) Synapsis
(c) Terminalisation of chiasmata
(d) Disappearance of nucleolus
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(b), (a,) (d), (c)
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(b), (a) (c), (d)
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(a), (b) (c), (d)
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(b), (c) (d), (a)
B.
(b), (a) (c), (d)
The correct sequence of events of meiosis are:
Synapsis in zygotene 
Crossing over in pachytene 
Terminalisation of chiasmata in diplotene 
Disappearance of nucleolus in diakinesis.
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Mock Test Series
Mock Test Series