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1.

Given below is the representation of a certain event at a particular stage of a type of cell division. Which is this stage A. Prophase-I during meiosisB. Prophase -II during meiosisC. Prophase of mitosisD. Both prophase and metaphase of mitosis

Answer» Correct Answer - A
During zygotene stage of prophase-I of meiosis-I, bivalent chromosomes clearly appear as tetrads. Pachytene stage is characterised by the appearance of recombination nodules, the sites at which crossing over (exchange of genetic material) occurs between non-sister chromatids of the homologous chromosomes.
Discussion
2.

A stage in cell division is shown in the figure. Select the answer which gives correct identification of the stage with its chracteristics A. Telophase - Nuclear envelope reforms, Golgi complex reformsB. Late anaphase - Chromosomes move away from equatorial plate, Golgi complex not presentC. Cytokinesis - Cell plate formed, mitochondria distributed between two daughter cellsD. Telophase - Endoplasmic reticulum and nucleolus not reformed yet

Answer» Correct Answer - A
Telophase is reverse of prophase. The chromosome that have reached their respective poles decondense, i.e., nuclear envelop reforms, Golgi complex reforms, etc. In late anaphase centromeres split and chromatid separate and chromatid move to opposite poles. Cytokinesis is process in which cell itself is divided two daughter cells.
Discussion
3.

Best stage to observe shape, size and number of chromosome isA. interphaseB. metaphaseC. prophaseD. telophase

Answer» Correct Answer - B
Metaphase can be characterised by the chromosomes that are least coiled which show maximum condensation and are shortest in length. It is the best state to study the structure. Size and number of chromosome is prepared at mataphase.
Discussion
4.

The stage at which cleavage or cytokinesis begins in animal cells isA. AnaphaseB. TelophaseC. `G_(0)`phaseD. Interphase

Answer» Correct Answer - A
In both plant and animal cells, cytokinesis begins before the end of anaphase.
Discussion
5.

Centromere is rquired forA. movement of chromosomes towards polesB. cytoplasmic cleavageC. crossing overD. transcription

Answer» Correct Answer - A
The arms of chromosome are known as chromatids. These arms are held together at a point called the centromere (or primary constriction). Centromere occurs any where along the length of chromosome. During cell division spindle fibres are attached to centromere and help in the movement of chromosomes towards the poles.
Discussion
6.

In which stage of the cell cycle are histone proteins synthesised in a eukaryotic cells ?A. During `G_(2)` - stage of prophaseB. During S-phaseC. During entire prophaseD. During telophase

Answer» Correct Answer - B
During S-phase of cell cycle synthesis of histone proteins takes place because at this stage the amount of DNA per cell get double to that of somatic number. Histone proteins are basic (absent in prokaryotes) DNA. DNA and histones together comprise chromatin, forming bulk of the eukaryotic chromosomes. Histones are of five major kinds H1, H2A, H2B and H4. H1 histones link neighbouring nucleosomes.
Discussion
7.

Which of the folliwng structure will not be common to mitotic cell of a higher plantA. Cell plateB. CentrioleC. CentromereD. Spindle fibres

Answer» Correct Answer - B
Centrosome is found in animals, Euglena, Nitella, some fungi and members of dinoflagellate. It is found near the nucleus.
Centriole is not common to mitotic cell of higher plants. Main function of centrosome is at time of cell division when the two centrioles separate and move on two poles. Aster and spindle are formed from it which help in the movement of chromatids. They form basal body, cilia, flagella , etc.
Centriole is rich in tubulin and ATPase.
Centrioles replicate in ` G_(2)` - phase of interphase of cell cycle but do not initiate cell division.
Discussion
8.

How many mitotic divisions are needed for a single cell to make 128cellsA. 7B. 14C. 28D. 64

Answer» Correct Answer - A
A single mitotic division results in the production of two cells from single cell.
Discussion
9.

Given below is schematic break-up of phases of cell cycle. Which one is correct matching ? A. B-metaphaseB. C-karyokinesisC. D-synthetic phaseD. A-cytokinesis

Answer» Correct Answer - C
Cell cycle completes in two steps, i.e. interphase and M-phase. Interphase is completed in three successive stages ` G_(1)` - phase (post mitotic phase), S-phase (synthetic phase) and ` G_(2)`- phase (premitotic or post synthetic phase). In the given figure. D is representing the S-phase (synthetic phase ) of cell cycle.
Discussion
10.

During which phase(s) of cell cycle amount of DNA in a cell remains at 4C level if the initial amount is denoted an 2CA. `G_(0)and G_(1)`B. `G_(1) and S`C. Only `G_(2)`D. ` G_(2) and M`

Answer» Correct Answer - D
During the S or synthetic phase, the DNA content doubles, i.e., from 2C to 4C for all diploid cells. The ` G_(2)` phase follows the S-phase and is called second growth phase or pre mitotic gap phase. In G_(2)` phase the synthesis of DNA stops therefore, the DNA level remains 4C if initial was 2C.
However, the formation of RNA and protein continue as they are required for the multiplication of cell organelles, spindle formation and cell growth. This amount becomes half (i.e.) 2C only during anaphase (in mitosis) when chromosomes separate.
Discussion
11.

Which one of the following precedes re-formation of the nuclear envelope during M phase of the cell cycle.A. Decondensation from chromosomes and reassembly of the nuclear laminaB. Transcription from chromosomes and reassembly of the nuclear laminaC. Fromation of the cntractile ring and formation of the phragmoplastD. Formation of the contractile ring and transcription form chromosomes

Answer» Correct Answer - A
At telophase stage, nuclear membrane vesicles associate with the surface of individual chromosomes and fuse to reform the nuclear membranes, which partially enclose clusters of chromosomes before coalescing to reform the complete nuclear envelope. During this process the nuclear pores reassemble and the dephosphorylated reassociate to form the nuclear lamina. One of the lamina proteins (lamina-B) remains with the nuclear membreane fragments throughout mitosis and may help nuclear reassembly. After the nucleus reforms, the chromosomes decondense and RNA synthesis resumes, causing the nucleolus to reappear.
Discussion
12.

In the somatic cell cycle.A. in `G_(1)`- phase DNA content is double the amount of DNA present in the original cellB. DNA replication takes place in S-phaseC. a short interphase is followed by a long mitotic phaseD. `G_(2)`- phase follows mitotic phase

Answer» Correct Answer - B
DNA replication occurs during S-phase of the mitotic cycle where it gets doubled as compared to that in the original cell.
Discussion
13.

Mitotic spindle is mainly composed of __ proteins.

Answer» Correct Answer - A
Spindle formed during mitosis and meiosis are nothing but microtubule complex. Microtubules are made up of small units of tubulin which has amino acid composition similar to actin.
Discussion
14.

Crossing over that results in genetic recombination in higher organisms occurs betweenA. sister chromatids of bivalentB. non-sister chromatids of a bivalentC. two daughter nucleiD. two different bivalents

Answer» Correct Answer - B
The process of crossing over takes place in pachytene stage of prophase-I of meiosis-I. In this process some genes of two non-sister chromatids of a bivalent are exchanged.
The process of crossing over is depicted
Sister chromatids of one
duplicate chromosome
Discussion
15.

Crossing over occurs betweenA. Sister chromatidsB. Non-sister chromatidsC. Homologous chromatidsD. Any two chromosomes

Answer» Correct Answer - C
It is between non-sister chromatids of homologous chromosomes.
Discussion
16.

In meiosis crossing over is initiated atA. leptoteneB. zygoteneC. diploteneD. pachytene

Answer» Correct Answer - D
Leptotene - Condensation of chromatin
Zygotene - Synapsis of homologous chromosomes
Pachytene - Crossing over
Diplotene - Dissolution of synaptonemal complex and appearance of chiasmata
Diakinesis - Terminalisation of chiasmata
Discussion
17.

Crossing over in diploid organism is responsible forA. dominance of genesB. linkage between genesC. segregation of allelesD. recombination of linked alleles

Answer» Correct Answer - D
The genes present on the same chromosome do not always remain together. These usually get separated and recombine with genes present on homologous chromosomes to form new combinations(recombinants).
Discussion
18.

Lampbrush chromosomes are visibleA. prophase of mitosisB. diplotene of meiosisC. metaphase of meiosisD. interphase

Answer» Correct Answer - B
Lampbrush chromosomes were reported by W Flemming (1882) and described by Ruckert (1892) from nuclei of yolk rich primary oocytes of newts and frog (amphibians). These are also found in spermatocytes of many animals. These are found in spermatocytes of many animals. These are found in permanent diplotene stage of meiosis and do not undergo cell cycle.
Each such chromosome has a double main axis made up of DNA and histones. The chromosomes are coiled and held at many places forming cross like structure called chiasmata. Loops arising laterally has uncoiled DNA which helps in rapid transcription and yolk synthesis.
Discussion
19.

The point at which the polytene chromosomes appeart to be attached togeher is known asA. centrioleB. centromereC. chromomereD. chromocentre

Answer» Correct Answer - D
Polytene chromosomes are infact formed by pairing of two somatic homologous chromosomes which undergo repeated endomitosis, forming a number of strands. These strands remain attached to a common large chromocentre of all polytene chromosomes and are rich in heterochromatin.
Discussion
20.

When cell has stalled DNA replication fork , which checkpoint should be predominantly activatedA. `G_(1)//S`B. ` G_(2)//M`C. MD. Both ` G_(2)//M and M`

Answer» Correct Answer - A
Stalled forks activate checkpoint signaling and pause replication. Since, ` G_(1)`/ S checkpoint checks DNA damage, cells size prior to S-phase (i.e. DNA replication phase), this checkpoint would be activated by stalled DNA replication fork.
Discussion
21.

Spindle can be observed best underA. Light microscopeB. Polarising microscopeC. Phase contrast microscopeD. Interference microscope

Answer» Correct Answer - b
generally electron microscopy is used to observe cytoskeleton due to their nanometrer size. however polarising microscopy a type of light microscopy and phase contrast microscopy can also be employed.
Discussion
22.

Spindle fibers attach on toA. kinetochore of the chromosomeB. centromere of the chromosomeC. kinetosome of the chromosomeD. telomere of the chromosome

Answer» Correct Answer - A
Spindle fibres attach to kinetochores of chromosomes during cell division. They help the chromosomes/chromatids to get separated to the two daughter cells. Towards opposite poles.
Discussion
23.

Meiosis-I is reductional division. Meiosis-II is equational division due toA. pairing of homologous chromosomesB. crossing overC. separation of chromatidsD. disjunction of homologous chromosomes

Answer» Correct Answer - C
Meiosis - I is called heterotypic division as the two chromatids of a chromosome become genetically different due to the crossing over. Number of chromosomes is reduced to half, hence, called reduction division. Meiosis-II is just like mitosis but occours in haploid nuclei, it is called homotypic or equational division as the chromosomes are distributed equally into daughter cells and chromosome number remains the same in daughter cells.
Discussion