1. Meiosis I is reductional division. Meiosis II is equational division due to
(a) pairing of homologous chromosomes
(b) crossing over
(c) separation of chromatids
(d) disjunction of homologous chromosomes
2. Segregation of mendelian factor (Aa) occurs during
(a) Diplotene
(b) Anaphase I
(c) Zygotene/Pachytene
(d) Anaphase II
3. Mitotic anaphase differs from metaphase in possessing
(a) same number of chromosomes and same number of chromatids
(b) half number of chromosomes and half number of chromatids
(c) half number of chromosomes and same number of chromatids
(d) same number of chromosomes and half number of chromatids
4. In meiosis, the daughter cells differ from parent cell as well as amongst themselves due to
(a) segregation, independent assortment and crossing over
(b) segregation and crossing over
(c) independent assortment and crossing over
(d) segregation and independent assortment
5. Number of chromatids at metaphase is
(a) two each in mitosis and meiosis
(b) two in mitosis and one in meiosis
(c) two in mitosis and four in meiosis
(d) one in mitosis and two in meiosis
6. Meiosis II performs
(a) separation of sex chromosomes
(b) synthesis of DNA and centromere
(c) separation of homologous chromosomes
(d) separation of chromatids
7. Best stage to observe shape, size and number of chromosomes is
(a) interphase
(b) metaphase
(c) prophase
(d) telophase
8. Meiosis is evolutionary significant because it result in
(a) genetically similar daughters
(b) four daughter cells
(c) eggs and sperms
(d) recombinations
9. The exchange of genetic material between chromatids of paired homologous chromosomes during first meiotic division is called
(a) transformation
(b) chiasmata
(c) crossing over
(d) synapsis
10. In cell cycle, DNA replication takes place in
(a) G1 phase
(b) G2 phase
(c) mitotic metaphase
(d) S phase
11. Lampbrush chromosomes occur during
(a) prophase of mitosis
(b) diplotene of meiosis
(c) metaphase of meiosis
(d) interphase
12. Colchicine is employed to diploidize a haploid cell as it
(a) inhibits mitosis
(b) inhibits formation of mitotic spindle
(c) allows replication of DNA twice in one cell cycle
(d) inhibits formation of centromere
13. Which one of the following structures will not be common to mitotic cells of higher plants?
(a) cell plate
(b) centriole
(c) centromere
(d) spindle fibres
14. The process by which the cytoplasm of a cell divides to form two daughter cells.
(a)Cytokinesis
(b) Prophase
(c) Metaphase
(d) Anaphase
15. In which phase of the cell cycle centriole move towards opposite poles of the cell?
(1) Anaphase
(2) Metaphase
(3)Telophase
(4) Prophase
16. In cell division, spindle fibres are made up of protein
(a) Myoglobin
(b) Tublin
(c) Albumin
(d) Myosin
17. During cell growth, DNA synthesis takes place in
(a) G 2 phase
(b) M phase
(c) S phase
(d) G1 phase
18. During cell division, the spindle fibres get attached to condensing chromosome at a highly differentiated region. This region is called as
(a) Chromosome
(b) chromocentre
(c) Centriole
(d) Kinetochore
19. What plant material is best suited for studying mitosis ?
(a) Anther
(b) Piece of cork
(c) Root of tips
(d) Shoot apex
20. If a diploid cell is treated with colchicine then it becomes
(a) triploid
(b) tetraploid
(c) diploid
(d) monoploid
21. In the somatic cell cycle
(a) In G1 phase DNA content is double the amount of DNA present in the original cell
(b) DNA replication takes place in S-phase
(c) a short interphase is followed by a long mitotic phase
(d) G2 phase follows mitotic phase
22. If you are provided with root-tips of onion in your class and are asked to count the chromosomes, which of the following stages can you most
conveniently look into?
(a) Metaphase
(b) Telophase
(c) Anaphase
(d) Prophase
23. Which one of the following precedes reformation of the nuclear envelope during M phase of the cell cycle
(a) Decondensation from chromosomes, and reassembly of the nuclear lamina
(b) Transcription from chromosomes, and reassembly of the nuclear lamina
(c) Formation of the contractile ring, and formation of the phragmoplast
(d) Formation of the contractile ring, and transcription from chromosomes
24. At what stage of the cell cycle are histone proteins synthesized in a eukaryotic cell?
(a) During G-2 stage of prophase
(b) During S-phase
(c) During entire prophase
(d) During telophase
25. During gamete formation, the enzyme recombinase participates during
(a) Metaphase – I
(b) Anaphase – II
(c) Prophase – I
(d) Prophase – II
26. Synapsis occurs between:
(a) mRNA and ribosomes
(b) spindle fibres and centromere
(c) two homologous chromosomes
(d) a male and a female gamete
27. During mitosis ER and nucleolus begin to disappear at:
(a) late prophase
(b) early metaphase
(c) late metaphase
(d) early prophase
28. Select the correct option with respect to mitosis.
(a) Chromatids separate but remain in the centre of the cell in anaphase.
(b) Chromatids start moving towards opposite poles in telophase.
(c) Golgi complex and endoplasmic reticulum are still visible at the end of prophase.
(d) Chromosomes move to the spindle equator and get aligned along equatorial plate in metaphase
29. At metaphase, chromosomes are attached to the spindle fibres by their:
(a) satellites
(b) secondary constrictions
(c) kinetochores
(d) centromere
30. During gamete formation, the enzyme recombinase participates during
(a) Metaphase – I
(b) Anaphase – II
(c) Prophase – I
(d) Prophase – II
31. 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 meiosis
(b) Prophase II during meiosis
(c) Prophase of Mitosis
(d) Both prophase and metaphase of mitosis.
32. Identify the meiotic stage in which the homologous chromosomes separate while the sister chromatids remain associated at their ntromeres?
(a) Metaphase I
(b) Metaphase II
(c) Anaphase I
(d) Anaphase II
33. The complex formed by a pair of synapsed homologous chromosomes is called
(a) Kinetochore
(b) Bivalent
(c) Axoneme
(d) Equatorial plate
34. During the metaphase stage of mitosis spindle fibres attach to chromosomes at
(a) Centromere
(b) Kinetochore
(c) Both centromere and kinetochore
(d) Centromere, kinetochore and areas adjoining contromere
35. During meiosis I, the chromosomes start pairing at
(a) Leptotene
(b) Zygotene
(c) Pachytene
(d) Diplotene
36. Transpiration is least in
(a) good soil moisture
(b) high wind velocity
(c) dry environment
(d) high atmospheric humidity
37. Anaphase Promoting Complex (APC) is a protein degradation machinery necessary for proper mitosis of animal cell. If APC is defective in a human cell, which of the following is expected to occur?
(a) Chromosomes will be fragmented
(b) Chromosomes will not segregate
(c) Recombination of chromosome arms will occur
(d) Chromosomes will not condense
38.Directions : Each of these questions contains an Assertion followed by Reason. Read them carefully and answer the question on the basis of following options. You have to select the one that best describes the two statements.
(a) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.
(c) If Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.
Assertion : Meiosis II is known as equational or homotypic division.
Reason :Meiosis II produces same number of chromosome in cell.
39. The association of more than one ribosome with a single molecule of m-RNA complex is called as…
(a) Polypeptide
(b) Polysome
(c) Polymer
(d) Poly Saccharide
40. When cell has stalled DNA replication fork, which checkpoint should be predominantly activated?
(a) G 1 /S
(b) M
(c) G 2 /M
(d) Both G 2 /M and M
41. Bacteria possess small DNA other than circular DNA which is called as…
(a) Cosmid
(b) Plasmid
(c) Plastid
(d) Starid
44.Spindle fibres attach on to
(a) kinetochore of the chromosome
(b) kinetosome of the chromosome
(c) centromere of the chromosome
(d) telomere of the chromosome
45. In which of the following matters mitosis and meiosis are similar ?
(a) Both are precede by DNA replication
(b) Both have pairing of homologous chromosomes
(c) Both process occurs in all kinds of cells
(d) Both include separation of paired chromosomes.
46. Identify the meiotic stage in which the homologous chromosomes separate while the sister chromatids remain associated at their centromeres.
(a) Metaphase I
(b) Metaphase II
(c) Anaphase I
(d) Anaphase II
47. Which of the following statement is/are correct for Prophase-I ?
(i) During diplotene, the members of each pair of homologous chromosomes start moving away from one another.
(ii) In zygotene, bivalent chromosomes appear tetravalent.
(iii) In diakinesis, chromatids become separated even at the site of chiasmata.
(a) only (i)
(b) only (ii)
(c) only (i) and (iii)
(d) (i), (ii) and (iii)
48. In meiosis crossing over is initiated at
(a) zygotene
(b) pachytene
(c) leptotene
(d) diplotene
49. A somatic cell that has just completed the S phase of its cell cycle, as compared to gamete of the same species, has
(a) twice the number of chromosomes and four times the amount of DNA
(b) four times the number of chromosomes and twice the amount of DNA
(c) twice the number of chromosomes and twice the amount of DNA
(d) same number of chromosomes but twice the amount of DNA
50. Indentify the correct sequence of karyokinesis stages
(a) Prophase, Anaphase, Metaphase, Telophase
(b) Prophase, Metaphase, Anaphase, Telophase
(c) Prophase, Telophase, Metaphase, Anaphase
(d) Prophase, Metaphase, Telophase, Anaphase
51.Which of the following is not a characteristic feature during mitosis in somatic cells?
(a) Chromosome movement
(b) Synapsis
(c) Spindle fibres
(d) Disappearance of nucleolus
52. During which phase(s) of cell cycle, amount of DNA in a cell remains at 4C level if the initial amount is denoted as 2C?
(a) G1 and S
(b) G0 and G1
(c) Only G2
(d) G2 and M
53. During meiosis I, the chromosomes start pairing at
(a) Zygotene
(b) Leptotene
(c) Diplotene
(d) Pachytene
54. Mitotic anaphase differs from metaphase in possessing
(a) same number of chromosomes and same number of chromatids
(b) half number of chromosomes and half number of chromatids
(c) half number of chromosomes and same number of chromatids
(d) same number of chromosomes and half number of chromatids.
55. How many mitotic divisions are needed for a single cell to make 128 cells?
(a) 28
(b) 32
(c) 7
(d) 14
56. During mitosis, ER and nucleolus begin to disappear at
(a) late prophase
(b) early metaphase
(c) late metaphase
(d) early prophase
57. At what stage of the cell cycle are histone proteins synthesized in a eukaryotic cell?
(a) During G 2 stage of prophase
(b) During entire prophase
(c) During telophase
(d) During Sphase
58. During the metaphase stage of mitosis, spindle fibres attach to chromosomes at
(a) kinetochore
(b) both centromere and kinetochore
(c) centromere, kinetochore and areas adjoining centromere
(d) centromere
59. Which of the following options gives the correct sequence of events during mitosis ?
(a) Condensation → nuclear membrane disassembly → arrangement at equator → centromere division → segregation → telophase
(b) Condensation → crossing over → nuclear membrane disassembly → segregation → telophase
(c) Condensation → arrangement at equator → centromere division → segregation → telophase
(d) Condensation → nuclear membrane disassembly → crossing over → segregation → telophase
60. 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 ?
(a) Chromosomes will be fragmented
(b) Chromosomes will not segregate
(c) Recombination of chromosome arms will occur
(d) Chromosomes will not condense
61. The stage during which separation of the paired homologous chromosomes begins is
(a) Pachytene
(b) Diplotene
(c) Zygotene
(d) Diakinesis
62. The correct sequence of phases of cell cycle is :
(1) M → G1→ G2 → S
(2) G1 → G2 → S → M
(3) S → G1 → G2 → M
(4) G1 → S → G2 → M
63. Cell in G0 phase :
(a) exit the cell cycle
(b) enter the cell cycle
(c) suspend the cell cycle
(d) terminate the cell cycle
64. Dissolution of the synaptonemal complex occurs during
(a) Diplotene
(b) Leptotene
(c) Pachytene
(d) Zygotene
65. Match the following with respect to meiosis
(a) Zygotene (i) Terminalization
(b) Pachytene (ii) Chiasmata
(c) Diplotene (iii)Crossing over
(d) Diakinesis (iv) Synapsis
Select the correct option from the following
(a) (b) (c) (d)
(1) (i) (ii) (iv) (iii)
(2) (ii) (iv) (iii) (i)
(3) (iii) (iv) (i) (ii)
(4) (iv) (iii) (ii) (i)
66. Some dividing cells exit the cell cycle and enter vegetative inactive stage. This is called quiescent stage (G0). This process occurs at the end of
(a) S phase
(b) G2 phase
(c) M phase
(d) G1 phase
67. Identify the correct statement with regard to G1 phase (Gap 1) of interphase.
(a) Cell is metabolically active, grows but does not replicate its DNA.
(b) Nuclear Division takes place.
(c) DNA synthesis or replication takes place.
(d) Reorganisation of all cell components takes place.
68. Which of the following stages of meiosis involves division of centromere?
(a) Telophase II
(b) Metaphase I
(c) Metaphase II
(d) Anaphase II
69. 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 (v) DNA replication
Choose the correct answer from the options given below.
(a) (b) (c) (d)
(1) (ii) (iv) (iii) (i)
(2) (iii) (ii) (i) (iv)
(3) (iv) (ii) (iii) (i)
(4) (iv) (i) (ii) (iii)
70. The fruit fly has 8 chromosomes (2n) in each cell. During interphase of Mitosis if the number of chromosomes at G1 phase is 8, what would be the number of chromosomes after S phase?
(a) 32
(b) 8
(c) 16
(d) 4
71. The centriole undergoes duplication during:
(a) G2 phase
(b) S-phase
(c) Prophase
(d) Metaphase
72. Which stage of meiotic prophase shows terminalisation of chiasmata as its distinctive feature?
(a) Pachytene
(b) Leptotene
(c) Zygotene
(d) Diakinesis
Solution
1. (c)Meiosis II is an equational division which is meant for maintaining the haploid number, separating the two chromatids of a chromosome.
2. (b)The paired homologous chromosomes separate in Anaphase I of meiosis I so that each gamete receives one chromosome of each homologous pair.
3. (d)In mitotic anaphase, the sister chromatids separate from each other and begin to move towards the opposite poles.
4. (d) Due to segeration , independent assortment and crossing over at time of meosis, daughter cells exihibits variations.
5. (a) In both mitotic and meiotic metaphase, the number of chromatids per chromosome is two.
6. (d) Meiosis II is homotypic division specially for maintanence of the haploid number, separating the chromatids from each other in a chromosome.
7. (b) During metaphase, the centomeres of the chromosome lie on the equatorial plate according to their size and spatial arrangement. So it is the best time to count the number and study the morphology of chromosomes.
8. (d) Meiosis provides a chance for new combinations of chromosome mainly by the phenomenon of crossing over and random distribution of homologous chromosomes between daughter cells.
9. (c)The points of attachment between homologous chromosomes after their separation in diplotene are called chiasmata. The process of pairing of homologous chromosomes is called synapsis the phenomenon by which DNA isolated from one type of cell, when introduced into another type, is able to bestow some of the properties of the former to the latter is known as transformation.
10. (d)G1 phase, also called Gap I phase is characterized by increase in cell size. In the S phase or synthetic phase DNA molecules replicate. G2 is the second growth phase. Gap II where in there is intensive formation of RNAs and proteins. In the mitotic metaphase, the chromosomes are arranged at the equatorial plate.
11. (b)Lampbrush chromosomes are highly elongated bivalent chromosomes of diplotene stage, which are held together by chiasmata and have a large number of lateral loops for rapid transcription.
12. (b)Colchicine is a mitotic poison which inhibits the appearance of spindle fibres.
13. (b)Plants cells do not have centrioles. Cell plate appears during cytokinesis in dividing cells. Centromere holds the sister chromatids in a chromosome , spindle fibres appears during metaphase.
14. (a)The process by which the cytoplasm of a cell divides to form two two daughter cells is known as cytokinesis.
15. (a) In mitosis, there are basically 4 phases, namely prophase, metaphase, anaphase, and telophase. During prophase, the chromosomes condense and become visible.
- The nuclear envelope breaks down and the nucleolus disappears. The centriole moves towards the opposite poles of the cell. During metaphase, the mitotic spindle is formed.
- The centrioles are present at opposite poles of the cells. Chromosomes are linked at the metaphase plate.
- During anaphase, sister chromatids are pulled towards the opposite poles. During telophase, the chromosomes are present at the opposite pole.
- The nuclear envelope surrounds each set of chromosomes.
16. (b)The spindle fibres involved in cell division is made of microtubules which are composed of protein tubulin. In cilia, the microtubules are arranged in 9+2 arrangement.
17. (c)
- Interphase is the period between two subsequent M phases and consists of three phases: G1, S phase (the period of DNA replication) and G2 phase.
- The G1 phase is the gap between M phase and S phase and is marked by synthesis of RNA and protein (excluding histones) and duplication of all cell content except DNA.
- S phase of DNA replication and cell division is followed by G2 phase during which cell double-checks the duplicated DNA content.
18. (d)The key feature of metaphase is the attachment of spindle fibers to kinetochores of chromosomes. Kinetochores are disc-shaped structure at the surface of the centromeres. These structures serve as the site of attachment of spindle fibres to the chromosomes that are moved toward poles. So, the correct answer is ‘Kinetochore’
19. (a) Anther cells are used to study mitosis.
20. (b) Colchicine inhibits spindle formation, due to which chromatids are unable to separate during anaphase which results in doubling of chromosomes. So, if a diploid cell is treated with colchicine, there is doubling of chromosomes and it becomes tetraploid,. Its an alkaloid obtained from Colchicum autumnale.
21. (b) DNA replication is restricted to S- phase of interphase. G2 phase is followed by the mitotic phase which is shorter than the inter phase. In G2 phase DNA content is double than the amount present in the original cell.
22. (a) Chromosomes are most distinct in the metaphase stage. In the telophase stage they regain their coiled composition. In anaphase the chromatids separate and move towards opposite poles. In prophase stage the chromosomes appear thread like and individual chromatids cannot be seen.
23. (b) At the beginning of M phase or mitotic phase the nuclear membrane and nucleolus disappear. The decondensation of chromosomes occur. But when nuclear envelop restart forming then nuclear lamina assemble and chromosomes start condensing.
24.(b) Histone proteins are synthesized during Sphase of cell cycle. S-phase or Synthetic phase.
25.(c) Recombinase enzyme catalyzes the exchange of short pieces of DNA between two long DNA strands particularly the exchange of homologous regions between the paired maternal and paternal chromosome in prophase – I.
26. (c) Synapsis (also called syndesis) is the pairing of two homologous chromosomes that occurs during prophase I (zygotene stage) of meiosis. The two chromosome move together and pairing of corresponding points along their lengths as they lie side to side. The resulting structure is called a
bivalent.
27. (d) During mitosis, endoplasmic reticulum and nucleus begins to disappear at early prophase. Also, nucleus and cell become spherical and DNA molecules condense to form shortened chromosome.
29. (d) In mitosis chromosomes move to the equator and get aligned along equatorial plate in metaphase.
30. (c)
Kinetochores are large protein complexes that bind the centromeres of chromosomes to the microtubules of mitotic spindle fibres during metaphase in the cell cycle.
31. (c)
Recombinase enzyme catalyzes the exchange of short pieces of DNA between two long DNA strands particularly the exchange of homologous regions between the paired maternal and paternal chromosome in prophase – I.
32. (a) Diagram represents crossing over that takes place in pachytes stage of prophase – I during meiosis.
33. (c) Anaphase I begins when the two chromosomes of each bivalent (tetrad) separate and start moving toward opposite poles of the cell as a result of the action of the spindle. In anaphase I the sister chromatids remain attached at their centromeres and move together toward the poles.
35. (b) During zygotene, second stage of meiosis I, homologous chromosomes start pairing together forming a complex structure called synaptonemal complex. The complex formed by a pair of synapsed homologous chromosome is called a bivalent or a tetrad. Crossing over occurs between non sister chromatids of bivalent in the next stage.
36. (d) Kinetochores are small disc –shaped structures at the surface of the centromeres which serve as the sites of attachment of spindle fibres to the chromosomes that are moved into position at the centre of the cell. Hence, the metaphase is characterised by all the chromosomes coming to lie at the equator.
37. (b) During zygotene, a substage of Prophase I of meiosis I, chromosomes start pairing together called synapsis. Such paired chromosomes are called as homologous chromosomes. A complex structure i.e., synaptonemal complex is formed by a pair of synapsed homologous chromosomes called a bivalent or a tetrad.
38. (d) Transpiration is a process of loss of water in the form of vapours from the aerial parts of the plants. Transpiration is inversely
proportional to the atmospheric humidity. The rate of transpiration would be higher when humidity is low
39.(b) 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.
40.(a) Meiosis II is known as equational or homotypic division like mitosis. It ensures the maintenance of constant number of chromosomes from generation to generation on a species
41. (b) The group of ribosomes bound to an mRNA molecule is called a polyribosome, or polysome. Each ribosome within the group functions independently to synthesize separate polypeptide chain.
42.(c) G2 / M check point ensures that DNA Replication is complete and no error is left.
43.(c) Plastid
44.(a)Spindle fiber during mitosis & meiosis are attached to kinetochore of the chromosome.
45.(b)Both have pairing of homologous chromosomes
46.(c)In anaphase I, the homologues are pulled apart and move apart to opposite ends of the cell. The sister chromatids of each chromosome, however, remain attached to one another and don’t come apart. Finally, in telophase I, the chromosomes arrive at opposite poles of the cell.
47.(c) only (i) and (iii)
48(b) pachytene
49(c)In diploid cells (somatic cells) during G1 phase, DNA content is 2C and chromosome number is 2n whereas in haploid cells (gamete) during G, phase, DNA content is 1C and chromosome number is n. S phase is marked by replication of DNA and the amount of DNA per cell is doubled i.e., it becomes 4C in somatic cells, whereas chromosome number remains same i.e.. In. Thus, a somatic cell which has just completed S phase, will have 4C DNA content but In chromosome number, while the gamete cell has 1C DNA content and n chromosome number.
50(b)Karyokinesis is the division of the nucleus that occurs in four stages. They are prophase, metaphase, anaphase and Telophase.
51 (b)Synapsis is the process of association of homologous chromosomes. It takes place during zygotene stage of prophase I of meiosis. This stage is not seen during mitosis.
52 (d)In M-phase, both 4C and 2C of DNA are present in different stages. S phase marks the period during which the amount of DNA in the cell doubles. Thus, at G 2phase the amount of DNA is 4C. These doubled cellular contents prepare the cell to sustain in the further mitotic division.
53 (a) During zygotene, a substage of Prophase I of meiosis I, chromosomes start pairing together called synapsis. Such paired chromosomes are called as homologous chromosomes. A complex structure i.e., synaptonemal complex is formed by a pair of synapsed homologous chromosomes called a bivalent or a tetrad
54.(b)Mitotic anaphase differs from metaphase in possessing same number of chromosomes and half number of chromatids. During anaphase of mitosis, chromosomes divide at the point of centromere or kinetochore and thus two sister chromatids are formed which are called as chromosomes. While during metaphase, chromosomes become maximally distinct due to further contraction and thus size of chromosomes is measured at mitotic metaphase.
55.(c) Mitosis is an equational division where after division each cell produces two daughter cells, therefore after 7 divisions one cell will give 128 cells in case of mitosis.
56.(d) During early prophase of mitosis, nucleus and cell become spheroid. Viscocity and refractivity of cytoplasm increases. DNA molecules condense to form shortened chromosome. Endoplasmic reticulum and nucleolus starts disappearing.
57. (d) During S phase or synthetic phase the replication of DNA takes place. For replication of DNA histone proteins are required so they are also synthesized during this phase. It takes about 30%- 50% of the total cell cycle. Prophase and telophase are stages involved in mitosis or meiosis. During G2 phase division of centrioles, mitochondria and chloroplasts occurs
58. (a) In metaphase, chromosomes consisting of two sister chromatids get arranged at equator. Discontinuous fibres radiate out from two spindle poles and get connected to the disc shaped structure at the surface of the centromere called kinetochores. These are known as chromosome fibres or tractile fibrils. A kinetochore is a complex protein structure that is analogous to a ring for the microtubule hook; it is the point where microtubules attach themselves to the chromosome.
59 (a) Mitosis consists of four basic phases: prophase, metaphase, anaphase, and telophase. First condensation of the chromatin occurs, to form compact chromosomes, nuclear membrane disassembly occurs (prophase). Then the chromosomes are arranged along the equator forming metaphase plate (metaphase). Then centromere division occurs and sister chromatids segregate (anaphase). Finally telophase occurs
60. (b) The anaphase-promoting complex/cyclosome (APC/C) is a multisubunit ubiquitin-protein ligase that targets for degradation cell-cycle regulatory proteins during exit from mitosis and in the G1 phase of the cell cycle. Anaphase Promoting Complex will lead to segregation of chromosomes and promote anaphase. But if APC is defective in a human cell, the chromosomes will not separate.
61(b) Prophase I is divided into 5 distinctive sub-stages:
Leptotene – The chromosomes begin to condense and are attached to the nuclear membrane via their telomeres
Zygotene – Synapsis begins with a synaptonemal complex forming between homologous chromosomes
Pachytene – Crossing over of genetic material occurs between non-sister chromatids
Diplotene – Synapsis ends with disappearance of synaptonemal complex; homologous pairs remain attached at chiasmata
Diakinesis – Chromosomes become fully condensed and nuclear membrane disintegrates prior to metaphase I
62 (d) The cell cycle is a four-stage process in which the cell increases in size (gap 1, or G1, stage), copies its DNA (synthesis, or S, stage), prepares to divide (gap 2, or G2, stage), and divides (mitosis, or M, stage). The stages G1, S, and G2 make up interphase, which accounts for the span between cell divisions.
63 (a) A cell cycle is a series of events that takes place in a cell as it grows and divides. The cell cycle is a four-stage process in which the cell increases in size (gap 1, or G1, stage), copies its DNA (synthesis, or S, stage), prepares to divide (gap 2, or G2, stage), and divides (mitosis, or M, stage). The stages G1, S, and G2 make up interphase, which accounts for the span between cell divisions
64(a) diplotene is a stage of meiotic prophase which follows the pachytene and during which the paired homologous chromosomes begin to separate and chiasmata become visible.
65 (d) Zygotene is that phase wherein the homologous chromosomes pair or come together in synapse. The pairing or coming together of homologous chromosomes is called synapsis. the actual “crossing-overs” of genetic material are thought to occur during the previous pachytene stage The chiasmata become visible during the diplotene stage of prophase I of meiosis, terminalization completion takes place in diakinesis.
66 (c) Some dividing cells at the end of mitotic phase exits the cell cycle and enter into a vegetative inactive stage, also called as quiescent phase.
Thus, the correct answer is (D).
67 (a) Cell division occurs during M phase, which consists of nuclear division followed by cytoplasmic division. The DNA is replicated in the preceding S phase; the two copies of each replicated chromosome (called sister chromatids) remain glued together by cohesins.
68 (d) Division of centromere occurs in anaphase II. Telophase II is the last stage of meiosis II. During this phase, the chromatids reach the poles and start uncoiling. Chromosomes form two parallel plates in metaphase I and one plate in metaphase II. 69 (d) Division of centromere occurs in anaphase II. Telophase II is the last stage of meiosis II. During this phase, the chromatids reach the poles and start uncoiling. Chromosomes form two parallel plates in metaphase I and one plate in metaphase II.
70 (d) S phase – DNA replication G2 phase – Proteins are synthesized Quiescent stage – Inactive phase G1 phase – Interval between mitosis and initiation of DNA replication
71 (b) During mitotic cell cycle if the chromosome number in G1 phase is 8 , it remains same till Metaphase. Hence, even after S phase same chromosome number 8 is maintained in the cell of fruit fly
72 (b) Centrioles duplicate in S phase of cell cycle
