101. Assertion: Centromere and kinetochore are not exact synonyms.
Reason: The centromere is the chromosome region joining sister chromatids, while kinetochores on its surface provide spindle-fibre attachment sites.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains the Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not correctly explain the Assertion
ⓒ. Assertion is true and Reason is false, so Reason cannot correctly explain the Assertion
ⓓ. Assertion is false and Reason is true, so Reason cannot correctly explain the Assertion
Correct Answer: Both Assertion and Reason are true, and Reason correctly explains the Assertion
Explanation: Both parts are true, and the structural distinction stated in the Reason explains the Assertion. Although centromeres and kinetochores are spatially associated, they refer to different structural features. The centromere is the chromosome region at which the sister chromatids remain joined before anaphase. Kinetochores are disc-shaped structures associated with the centromeric surface and serve as binding sites for spindle fibres. The reason accurately states this distinction and directly explains why the two terms cannot be used interchangeably. Understanding the difference is important when interpreting metaphase: sister chromatids remain connected through the centromeric region, while each chromatid interacts with the spindle through its own kinetochore. This distinction allows spindle attachment to be discussed precisely without treating the attachment structure as the entire centromeric chromosome region.
102. Control cells form spindle fibres that attach to chromosomes and produce a clear metaphase plate. Treated cells form an apparently bipolar spindle, but their chromosomes remain scattered and show no stable spindle attachment. The treatment most directly affected:
ⓐ. chromosome replication during S phase
ⓑ. chromosome condensation during prophase
ⓒ. kinetochore function during metaphase
ⓓ. nuclear-envelope reformation during telophase
Correct Answer: kinetochore function during metaphase
Explanation: The treated cells possess a bipolar spindle, so basic pole and spindle formation has occurred. Their chromosomes are also present but remain scattered and fail to establish stable spindle attachment. Kinetochores are the chromosome-associated sites through which spindle fibres attach at metaphase. Loss of kinetochore function explains both observations: spindle fibres exist, yet they cannot connect normally to the chromosomes or generate the forces required for equatorial alignment. A replication defect would alter DNA duplication before mitosis, while a condensation defect would prevent formation of distinct mitotic chromosomes. Nuclear-envelope reformation is a telophase event and cannot account for failure of metaphase attachment. The experiment localises the disruption to the chromosome-spindle interface. Preserved events act as internal controls, showing which earlier parts of the sequence remain functional. The strongest conclusion distinguishes the direct observation from the later consequence inferred from it.
103. A replicated chromosome is positioned between two spindle poles. The kinetochore of one sister chromatid is connected to pole P, while the kinetochore of the other sister chromatid is connected to pole Q. This arrangement represents:
ⓐ. pairing of homologous chromosomes during zygotene
ⓑ. normal bipolar attachment during mitotic metaphase
ⓒ. centromere division during mitotic anaphase
ⓓ. nuclear-envelope reconstitution during telophase
Correct Answer: normal bipolar attachment during mitotic metaphase
Explanation: During mitotic metaphase, the sister chromatids of each replicated chromosome remain joined at the centromere. Their kinetochores interact with spindle fibres oriented towards opposite poles. One sister kinetochore connects with one pole, while the other connects with the opposite pole, producing bipolar attachment. This geometry prepares the chromosome for equal sister-chromatid separation when the centromere divides at anaphase. The description does not involve homologous pairing, which is a feature of meiotic prophase I. It also precedes centromere division and does not include telophase reconstitution. The opposite-pole orientation is the crucial spatial relation linking metaphase attachment with later equal chromosome distribution. Centromere division changes the counting status of chromatids, converting them into independently counted daughter chromosomes without synthesising additional DNA.
104. Four replicated chromosomes show the attachment patterns listed below.
| Chromosome | Kinetochore of sister P | Kinetochore of sister Q | Position |
|---|
| W | Pole 1 | Pole 1 | Near Pole 1 |
| X | No attachment | Pole 2 | Off-centre |
| Y | Pole 1 | Pole 2 | At equator |
| Z | No attachment | No attachment | Scattered |
Which chromosome displays the normal mitotic metaphase arrangement?
ⓐ. Chromosome W
ⓑ. Chromosome Y
ⓒ. Chromosome X
ⓓ. Chromosome Z
Correct Answer: Chromosome Y
Explanation: Chromosome Y has one sister kinetochore connected to Pole \(1\) and the other connected to Pole \(2\). It is also positioned at the equator. This is the normal bipolar arrangement for a mitotic metaphase chromosome. Opposing spindle connections generate the balanced orientation required for alignment at the metaphase plate and prepare the sister chromatids for movement towards opposite poles after centromere division. Chromosome W has both sisters connected towards the same pole, while X has only one attached sister and remains off-centre. Z lacks spindle attachment entirely. The correct row must satisfy both attachment geometry and position; equatorial location alone would not be sufficient without opposite-pole connections. The table should be read across each row before comparing rows, since the decisive evidence is the combined pattern rather than any single entry. The inference comes from the complete row pattern; one isolated value could fit more than one stage or process.
105. Both sister kinetochores of a replicated mitotic chromosome become attached to spindle fibres leading towards the same pole. If the condition persists, the most likely consequence is:
ⓐ. faulty bipolar orientation with unequal chromosome segregation
ⓑ. normal metaphase alignment followed by equal sister separation
ⓒ. pairing of the chromosome with its homologue as a bivalent
ⓓ. chromosome decondensation before nuclear-envelope breakdown
Correct Answer: faulty bipolar orientation with unequal chromosome segregation
Explanation: Normal mitotic metaphase requires the two sister kinetochores to connect with opposite spindle poles. This bipolar orientation places the chromosome under opposing forces and prepares the sisters for movement into different daughter regions. If both kinetochores face the same pole, the chromosome lacks the normal two-pole geometry. Stable equatorial positioning may fail, and later distribution of the sister-derived chromosomes may become unequal if the abnormal attachment persists. Homologous pairing is restricted to meiosis I and is not produced by altered mitotic attachment. Chromosome decondensation is associated with telophase rather than spindle orientation. The prediction follows from the mechanical relationship between opposite-pole attachment and equal segregation. Equal distribution is evaluated at the future daughter poles; a transient doubling of chromosome count in the undivided cell does not represent a new round of replication.
106. Assertion: The metaphase plate is a permanent membrane located at the centre of the cell.
Reason: Spindle forces position replicated chromosomes along an equatorial plane during metaphase.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains the Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not correctly explain the Assertion
ⓒ. Assertion is true and Reason is false, so Reason cannot correctly explain the Assertion
ⓓ. Assertion is false and Reason is true, so Reason cannot correctly explain the Assertion
Correct Answer: Assertion is false and Reason is true, so Reason cannot correctly explain the Assertion
Explanation: A metaphase plate is an equatorial chromosome arrangement, not a permanent membrane, so the Assertion is false. The metaphase plate is not a membrane or a pre-existing cellular structure. It is an imaginary equatorial plane describing the common alignment of metaphase chromosomes. The reason is true: spindle attachments and the resulting forces position the replicated chromosomes at this equatorial region. Each chromosome remains composed of two sister chromatids joined at the centromere, with their kinetochores connected towards opposite poles. The reason identifies how the alignment is produced, but it does not support the membrane claim. The metaphase plate should be understood as a spatial arrangement created by chromosome-spindle interactions, not as a physical partition within the cell. The plate disappears as an arrangement once centromeres divide and daughter chromosomes leave the equator.
107. Control cells form a compact metaphase plate. In treated cells, kinetochores remain attached to spindle fibres, but the fibres cannot generate effective movement, and chromosomes stay scattered. The strongest inference is that:
ⓐ. chromosome condensation depends on completed cytokinesis
ⓑ. kinetochore attachment normally begins only after centromere division
ⓒ. spindle forces are needed for equatorial chromosome alignment
ⓓ. nuclear-envelope reformation produces the metaphase plate
Correct Answer: spindle forces are needed for equatorial chromosome alignment
Explanation: The treatment does not prevent kinetochore attachment, so the chromosome-spindle connection is present. The distinctive failure is the absence of effective movement and equatorial alignment. During metaphase, spindle forces act through kinetochore attachments to position replicated chromosomes at the cell equator, producing the metaphase plate. This plate is an arrangement of chromosomes rather than a permanent membrane. The experiment separates attachment from force generation: attaching a chromosome to spindle fibres is not sufficient if those fibres cannot move or balance it appropriately. Centromere division occurs later, at the beginning of anaphase, while nuclear-envelope reformation belongs to telophase. The observed scattering specifically links functional spindle forces with metaphase alignment. The absence of a later product is interpreted through the first failed prerequisite, not as evidence that every earlier event also failed.
108. Consider the following statements about the metaphase plate.
I. It represents the equatorial alignment of replicated chromosomes.
II. It is produced through chromosome interactions with the spindle.
III. It is a permanent membrane separating the future daughter cells.
IV. Sister chromatids remain joined while chromosomes occupy it.
ⓐ. I and III only
ⓑ. II and IV only
ⓒ. I, II, III and IV
ⓓ. I, II and IV only
Correct Answer: I, II and IV only
Explanation: The metaphase plate is an imaginary equatorial plane defined by the common alignment of metaphase chromosomes. Spindle fibres attach through kinetochores and generate the positioning forces that bring chromosomes to this region. Each chromosome remains replicated at this stage, with its two sister chromatids still connected at the centromere. The metaphase plate is not a membrane, wall or permanent partition. It disappears as an organised arrangement when centromeres divide and daughter chromosomes begin moving towards opposite poles in anaphase. The valid statements combine the location, mechanism and chromosome state associated with metaphase. Treating the plate as a physical barrier confuses a temporary spatial arrangement with the later structures involved in cytokinesis.
109. Arrange the following events from established metaphase to progressing anaphase.
P. Replicated chromosomes occupy the metaphase plate.
Q. Centromeres divide.
R. Sister chromatids become independent daughter chromosomes.
S. Daughter chromosomes move towards opposite poles.
ⓐ. P → Q → R → S
ⓑ. Q → P → R → S
ⓒ. P → R → Q → S
ⓓ. R → Q → P → S
Correct Answer: P → Q → R → S
Explanation: At established metaphase, replicated chromosomes are aligned at the metaphase plate, and the sister chromatids remain joined at their centromeres. Anaphase begins when the centromeres divide. This structural change releases the sister chromatids from one another, and each former chromatid is then regarded as an independent daughter chromosome. The spindle-associated movement of these daughter chromosomes towards opposite poles follows their separation. The order is based on dependency: chromatids cannot become independent chromosomes before their shared centromere divides, and poleward migration cannot distribute them as separate units while they remain joined. This sequence converts the metaphase arrangement into two equivalent chromosome groups. Whole-cell chromosome counts during anaphase differ from counts at one pole as the cell has not yet been partitioned into daughter compartments. This dependency ensures that each future daughter nucleus receives one copy of every replicated chromosome.
110. A replicated chromosome lies at the equator with its sister chromatids joined at one constriction. The constriction divides, and the two resulting structures begin moving towards opposite poles. The cell has entered:
ⓐ. prophase, as chromosome condensation has just begun
ⓑ. metaphase, as chromosomes have only reached the equator
ⓒ. telophase, as daughter nuclei are being reconstituted
ⓓ. anaphase, as sister chromatids become daughter chromosomes
Correct Answer: anaphase, as sister chromatids become daughter chromosomes
Explanation: The decisive event is division of the centromeric constriction. Before this division, the two sister chromatids form one replicated chromosome. Once the centromere splits, the chromatids separate and each is counted as an independent daughter chromosome. Their movement towards opposite poles is the characteristic migration of mitotic anaphase. Metaphase would retain the sister connection and equatorial alignment, while telophase begins after the daughter chromosomes approach or reach the poles and nuclear reconstitution starts. The description links structural change with stage identity: centromere division initiates anaphase, changes chromosome counting and permits the two replicated copies to enter opposite daughter chromosome groups. The metaphase plate is an equatorial arrangement, not a membrane; its significance lies in preparing balanced poleward distribution.
111. A diploid cell with \(2n=12\) has entered mitotic anaphase, but cytokinesis has not begun. All centromeres have divided. The complete undivided cell now contains:
ⓐ. \(12\) daughter chromosomes and \(2C\) DNA
ⓑ. \(24\) daughter chromosomes and \(4C\) DNA
ⓒ. \(24\) daughter chromosomes and \(8C\) DNA
ⓓ. \(12\) replicated chromosomes and \(4C\) DNA
Correct Answer: \(24\) daughter chromosomes and \(4C\) DNA
Explanation: Before S phase, the diploid cell contains \(12\) chromosomes and \(2C\) DNA. Replication doubles DNA amount to \(4C\), but the chromosome count remains \(12\) while sister chromatids share their centromeres. At anaphase, all \(12\) centromeres divide. The two chromatids of every replicated chromosome become independent daughter chromosomes, giving:
\[
12\times2=24\ \text{daughter chromosomes}
\]
The cell is still one undivided cellular unit, so its total DNA remains \(4C\). The DNA will be partitioned into two \(2C\) daughter nuclei and later into two cells. This transient chromosome-count increase results from the centromere-based counting convention, not from another round of DNA replication. Centromere division changes the counting status of chromatids, converting them into independently counted daughter chromosomes without synthesising additional DNA. The metaphase plate is an equatorial arrangement, not a membrane; its significance lies in preparing balanced poleward distribution. Each pole receives the original diploid complement of \(12\) chromosomes even though the undivided anaphase cell temporarily contains \(24\).
112. Assertion: Division of centromeres marks the initiation of mitotic anaphase.
Reason: Centromere division immediately reduces the chromosome number of the undivided cell to half.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains the Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not correctly explain the Assertion
ⓒ. Assertion is true and Reason is false, so Reason cannot correctly explain the Assertion
ⓓ. Assertion is false and Reason is true, so Reason cannot correctly explain the Assertion
Correct Answer: Assertion is true and Reason is false, so Reason cannot correctly explain the Assertion
Explanation: The assertion is true. At the beginning of mitotic anaphase, the centromeres divide and release the sister chromatids from one another. Each former chromatid then becomes an independent daughter chromosome capable of moving towards a spindle pole. The reason is false since chromosome number does not become half within the undivided cell at that moment. Counting chromosomes by centromeres produces a temporary doubling of the chromosome count after all centromeres split. Equal poleward distribution later gives each daughter nucleus the original parental chromosome number. Anaphase initiation must be distinguished from the final chromosome count per daughter: separation first increases the number of independently counted chromosomes in the whole cell, then partitions them equally.
113. Four mitotic cells show the following chromosome states.
| Cell | Centromeres | Sister association | Chromosome movement |
|---|
| P | Unsplit | Present | Alignment at equator |
| Q | Split | Absent | Movement towards opposite poles |
| R | Separated | Absent | Decondensation at poles |
| S | Unsplit | Present | Condensation beginning |
Which cell is undergoing anaphase?
ⓐ. Cell P
ⓑ. Cell R
ⓒ. Cell Q
ⓓ. Cell S
Correct Answer: Cell Q
Explanation: Anaphase begins when centromeres divide and sister chromatids separate. Once released, the former chromatids are independent daughter chromosomes that migrate towards opposite spindle poles. Cell Q contains this complete combination: split centromeres, loss of sister association and poleward chromosome movement. Cell P is in metaphase, where replicated chromosomes remain joined and aligned at the equator. Cell R has progressed into telophase, as the chromosomes have reached the poles and begun decondensing. Cell S represents prophase chromosome condensation before metaphase alignment. The stage cannot be identified reliably from chromosome position alone; centromere state and the direction of chromosome change provide the decisive linked evidence. The table converts several observations into one stage decision by requiring their biological compatibility. The table should be read across each row before comparing rows, since the decisive evidence is the combined pattern rather than any single entry.
114. A treatment allows chromosomes to condense, attach bipolarly and align at the metaphase plate, but it prevents centromere division. If the treatment remains active, the most immediate result will be:
ⓐ. sister chromatids remain joined, preventing normal anaphase
ⓑ. two nuclear envelopes form around an unchanged metaphase plate
ⓒ. homologous chromosomes pair and form bivalents
ⓓ. daughter chromosomes reach the poles but fail to decondense
Correct Answer: sister chromatids remain joined, preventing normal anaphase
Explanation: Metaphase preparation has been completed: chromosomes are condensed, attached to opposite poles and aligned at the equator. The next essential event is centromere division. This releases sister chromatids so that spindle-associated forces can move them into opposite daughter chromosome groups. If centromeres cannot divide, the sisters remain physically connected and normal anaphase segregation cannot begin. Poleward movement of independent daughter chromosomes is prevented even though the earlier attachment geometry is correct. Homologous pairing is a meiotic prophase I event and is unrelated to this mitotic block. Nuclear-envelope formation normally occurs only after chromosome groups have been segregated. The treatment identifies centromere division as the transition linking metaphase alignment to anaphase movement. The experimental design separates two coordinated events by allowing one to proceed while selectively disrupting the other. The conclusion remains limited to the supplied treatment and observations; broader causal claims would require additional evidence.
115. Use the arrangement described here: several V-shaped daughter chromosomes move away from the equator. The pointed constricted region of each V is closest to its destination pole, while the arms extend behind it. This orientation indicates that:
ⓐ. chromosome arms pull the centromeres towards the equator
ⓑ. kinetochores disappear before chromosome movement begins
ⓒ. daughter chromosomes decondense as they leave the metaphase plate
ⓓ. centromeres lead while chromosome arms trail during anaphase
Correct Answer: centromeres lead while chromosome arms trail during anaphase
Explanation: During mitotic anaphase, spindle fibres are attached at kinetochores associated with the centromeric region. As daughter chromosomes move poleward, this attachment region is directed towards the pole. The remaining chromosome arms extend behind it, producing the characteristic described orientation. The orientation is useful for recognising both stage and direction of movement: the cell is distributing independent daughter chromosomes, not aligning replicated chromosomes at the equator. Decondensation occurs later, after the chromosome groups approach the poles during telophase. The spatial description shows that poleward migration is organised around the centromere-kinetochore region, giving the general rule that centromeres lead and arms trail. During normal anaphase, centromeres lead and chromosome arms trail, linking chromosome shape with the direction of poleward movement. The V-shaped orientation reflects movement from the centromeric attachment region, with chromosome arms following behind it.
116. A fluorescent marker is placed at the centromere of each chromosome, while a second marker labels the chromosome ends. During time-lapse imaging, the centromere markers remain closer to the approaching poles than the end markers. The observation supports the inference that:
ⓐ. chromosome arms attach directly to opposite spindle poles
ⓑ. daughter chromosomes migrate with centromeres leading
ⓒ. centromeres remain at the equator throughout anaphase
ⓓ. chromosome decondensation drives poleward movement
Correct Answer: daughter chromosomes migrate with centromeres leading
Explanation: The two markers distinguish the centromeric region from the chromosome arms. During poleward movement, the centromere marker consistently occupies the forward position, while the terminal marker follows behind. This provides direct positional evidence that daughter chromosomes move with their centromeres leading and their arms trailing. The observation fits spindle attachment through kinetochores on the centromeric surface. It does not suggest that chromosome arms attach independently to the poles. A centromere remaining at the equator would not show the measured approach towards a pole. Decondensation is mainly a telophase event and cannot explain the forward position of the centromere during anaphase. The experiment converts a descriptive rule of chromosome orientation into an observable spatial prediction. The relative marker positions reveal movement orientation without requiring direct visualisation of every spindle fibre. This makes the inference independent of chromosome-arm length.
117. Evaluate the following statements about mitotic anaphase.
I. Centromeres divide at its initiation.
II. Sister chromatids become independent daughter chromosomes.
III. Daughter chromosomes move with their arms leading.
IV. Equivalent chromosome groups move towards opposite poles.
ⓐ. I and III only
ⓑ. II and IV only
ⓒ. I, II and III only
ⓓ. I, II and IV only
Correct Answer: I, II and IV only
Explanation: Statement I identifies the event that initiates anaphase: division of the centromeres. This releases the sister chromatids, making statement II valid. Once separated, each former chromatid is counted and treated as an independent daughter chromosome. Statement IV describes the functional outcome of anaphase, in which equivalent chromosome groups move towards opposite poles. Statement III reverses the normal orientation. The centromeric region leads during poleward movement, while the chromosome arms trail behind. The valid combination integrates the initiating structural change, the resulting change in chromosome identity and the direction of segregation. Together, these events convert one metaphase chromosome set into two spatially separated daughter chromosome sets. The anaphase count for the entire undivided cell includes both moving groups, whereas the count at either pole represents only one future daughter set.
118. Arrange the following events from late anaphase through telophase.
P. Daughter chromosomes approach opposite poles.
Q. Chromosomes begin elongating and decondensing.
R. Nuclear envelopes form around the chromosome groups.
S. Nucleoli and organised endomembrane structures reappear.
ⓐ. Q → P → S → R
ⓑ. P → Q → R → S
ⓒ. P → R → Q → S
ⓓ. R → S → P → Q
Correct Answer: P → Q → R → S
Explanation: Late anaphase brings the daughter chromosomes towards opposite poles. As the cell enters telophase, the chromosomes begin elongating and losing their highly condensed mitotic appearance. Nuclear envelopes then form around the two chromosome groups, establishing daughter nuclei. Nucleoli reappear, and the Golgi complexes and endoplasmic reticulum return towards an interphase-like organisation. These events overlap to some extent since mitosis is progressive, but the broad order follows a clear biological transition from chromosome movement to nuclear reconstitution. Nuclear envelopes cannot normally enclose properly organised daughter sets before segregation has placed those sets at opposite poles. The sequence shows how telophase reverses several structural changes established during prophase. Arrival at opposite poles establishes the spatial basis for two nuclei, while decondensation restores an interphase-like chromosome organisation. Reassembly follows segregation, ensuring that each new envelope surrounds an already separated chromosome complement.
119. A graph plots chromosome-condensation level on the y-axis against progression from prophase to telophase on the x-axis. The curve rises during prophase, reaches its maximum around metaphase and falls after chromosomes arrive at the poles. The falling region most directly represents:
ⓐ. chromosome decondensation as telophase progresses
ⓑ. centriole duplication during interphase S phase
ⓒ. sister-chromatid separation at anaphase onset
ⓓ. chromosome alignment at the metaphase plate
Correct Answer: chromosome decondensation as telophase progresses
Explanation: The graph follows the physical compactness of chromosomes across mitosis. Condensation increases during prophase and is maximal at metaphase, when chromosome morphology is especially distinct. Anaphase chromosomes remain sufficiently condensed for organised poleward movement. After the daughter chromosome groups reach the poles, the condensation level falls as chromosomes elongate and decondense during telophase. They progressively lose their identity as separate, sharply visible mitotic chromosomes and return towards an interphase chromatin organisation. Centriole duplication occurs earlier in S phase and lies outside the plotted mitotic interval. Metaphase alignment corresponds to the high region of the curve, not the falling region. The downward trend identifies the structural reversal associated with telophase. Graph interpretation depends on the stated axes and observation unit; a curve for one cell cannot be read as a curve for the whole culture.
120. Assertion: Chromosomes lose their distinct mitotic identity during telophase.
Reason: Chromosomes become increasingly condensed after reaching opposite poles.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains the Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not correctly explain the Assertion
ⓒ. Assertion is true and Reason is false, so Reason cannot correctly explain the Assertion
ⓓ. Assertion is false and Reason is true, so Reason cannot correctly explain the Assertion
Correct Answer: Assertion is true and Reason is false, so Reason cannot correctly explain the Assertion
Explanation: Distinct mitotic chromosomes lose their sharply condensed identity during telophase, making the Assertion true. During telophase, daughter chromosomes that have reached opposite poles begin to elongate and decondense, so they gradually lose the sharply distinct appearance characteristic of mitotic chromosomes. The reason is false since it states the opposite change: condensation increases from prophase to metaphase, whereas telophase reverses that organisation. Nuclear envelopes form around the decondensing chromosome sets, nucleoli reappear, and Golgi complexes and endoplasmic reticulum regain an interphase-like organisation. The loss of distinct mitotic chromosome identity is linked with decondensation and nuclear reconstruction, not with further compaction after poleward movement. This reversal prepares the daughter nuclei for the next interphase. Decondensation is part of restoring functional daughter nuclei rather than an extension of metaphase compaction.
