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Cell Cycle and Cell Division

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Question
CBSEENBI11002057
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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

  • polyploidy

  • somaclonal variation

  • polyteny

  • aneuploidy

Solution

A.

polyploidy

Polyploid cells have a chromosome number that is more than double the haploid number.

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Question
CBSEENBI11002318
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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

  • twice the number of chromosomes and four times the amount of DNA

  • same number of chromosomes but twice the amount of DNA

  • twice the number of chromosomes and four times the amount of DNA

  • four times the number of chromosomes and twice the amount of DNA

Solution

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

Question
CBSEENBI11002116
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A stage in cell division is shown in the figure. Select the answer which gives correct identification of the stage with its characteristics

  • Telophase

    Nuclear envelope reforms, Golgi  complex reforms




  • Late anaphase

    Chromosomes move away from equatorial plate, Golgi complex not present

  • Cytokinesis

    Cell plate formed, Mitochondria distributed between  two daughter cells

  • Telophase

    Endoplasmic reticulum and nucleolus not reformed yet

Solution

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.

Question
CBSEENBI11002718
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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?

  • Chromosomes will not condense

  • Chromosomes will be fragmented

  • Chromosomes will not segregate

  • Recombination of chromosome arms will occur

Solution

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.

Question
CBSEENBI11002148
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Arrange the following events of meiosis in correct sequence:
(a) Crossing over
(b) Synapsis
(c) Terminalisation of chiasmata
(d) Disappearance of nucleolus

  • (b), (a,) (d), (c)

  • (b), (a) (c), (d)

  • (a), (b) (c), (d)

  • (b), (c) (d), (a)

Solution

B.

(b), (a) (c), (d)

The correct sequence of events of meiosis are:
Synapsis in zygotene rightwards arrowCrossing over in pachytene rightwards arrowTerminalisation of chiasmata in diplotene rightwards arrow Disappearance of nucleolus in diakinesis.

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