NCERT Exemplar MCQs

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(d) Meiosis is a reduction division that reduces the number of chromosomes to half in gametes. Since it is a special kind of cell division in which exchange of genetic material takes place that brings about variation in the next generations. So all options are characteristic features of meiotic cell division.

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(d) The genetic constitute of gametes is finally decided at the anaphase-I after which each cell receives half the chromosome number,r i.e., from ‘2 n’ in parent cell it changes to ‘n’ in daughter cells. During this phase, the two homologue of each chromosome pair separates and move toward opposite poles drawn by the microtubule of the spindle apparatus.

These are separated further by anaphase-II, wherein sister chromatids of each chromosome separate and move toward opposite poles. It can not be metaphase-I or metaphase-II because during these stages. The chromosomes or chromatids, merely arrange themselves at the metaphasic plate.

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(a) Meiosis occurs in sexually reproducing organisms to reduce the chromosome number to half before their gametes unit, so, as to maintain the constant chromosome number (2 n) in the progery.

Vegetative reproduction is a kind of asexual reproduction occurring in plants and does not involve the formation and fusion of gametes.

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(a) During Anaphase-I homologous chromosomes separate, while sister chromatids remain associated at their centromeres.

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(b) Mitosis is characterised by equal division because the chromosome numbers in the daughter cells remain the same as that of the parent cell. While reduction division is the characteristic of meiosis.

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(c) The complex formed by a pair of synapsed homologous chromosomes is called bivalent or a tetrad. It has two centromeres and four chromatids. 

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(c) \(\mathrm{G}_{0}, \mathrm{G}\) signifies growth. and zero means no growth takes place at this stage. It is also called quiescent stage \(\left(G_{0}\right)\). Some cells of the body like heart cells, neuron which do not divide, exit at \(\mathrm{G}_{1}\) stage and enter \(\mathrm{G}_{0}\) of the cell cycle which is an inactive stage.
The cells in this stage remain metabolically active but no longer proliferate unless called on to do so depending on the requirement of the organism.

\(\mathrm{G}_{1}\) phase is the first growth phase on post-mitotic gap phase that lasts between the and of mitotic cycle and the initiation of DNA replication.
\(\mathrm{G}_{2}\) phase is the second growth phase or premitotic gap phase in which the cell prepares itself to eates cell division, i.e., mitosis.

S-phase is the synthetic phase in which chromosomes replicate, i.e., DNA replication, formation of new chromatin fibres, etc.

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(d) Crossing Over is the phenomenon of genetic exchange between homologous pair of chromosomes and is a characteristic feature of meiotic cell division. It does not occur in mitosis. Rest of the options represent stages in mitosis.

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(d) Two cycles of DNA replication do not occur in meiosis. Other options (a), (b), and (c) define the meiotic cell division.

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(b) \(\mathrm{G}_{1}\) phase means gap 1 phase. It is the interval between mitosis and the initiation of DNA replication. The cell is metabolically active and continuously grows but does not replicate the DNA content. The cell also synthesizes proteins that are required for DNA replication.
Rest of the options are not characteristics of \(G_{1}\) phase.