Among eukaryotes, replication of DNA takes place in
AI-generated explanation. Check against your textbook.
Explanation:
In eukaryotes, DNA replication occurs during the S (Synthesis) phase of the cell cycle. During this phase, the DNA is duplicated so that each daughter cell receives an identical copy. Other phases have different roles: G1 is cell growth, G2 checks and prepares for division, and M phase is when mitosis and cytokinesis occur, separating the duplicated chromosomes.
🧠 Did You Know?
DNA replication is a tightly regulated process ensuring each chromosome is copied once before division, preventing errors.
💡 NCERT Memory Line:
DNA replication occurs in the S phase of the cell cycle in eukaryotes.
Which of the following stages of meiosis involves division of centromere?
AI-generated explanation. Check against your textbook.
Explanation:
Centromere division (sister chromatids separate) occurs during anaphase II of meiosis. In meiosis I, homologous chromosomes separate, but sister chromatids stay together at the centromere. During metaphase I/II, chromosomes align at the equator; the centromere does not divide yet. Telophase involves chromosome de-condensation and cytokinesis begins, not centromere splitting. Therefore, the correct stage is Anaphase II, when the centromeres split and sister chromatids move to opposite poles.
🧠 Did You Know?
Only in Anaphase II do the duplicated chromatids become separate chromosomes that migrate to opposite poles.
The process of appearance of recombination nodules occurs at which sub stage of prophase I in meiosis?
AI-generated explanation. Check against your textbook.
Explanation:
The recombination nodules appear during the pachytene stage of prophase I. This is the stage when crossing-over between homologous chromosomes occurs, facilitated by synapsis. Thus, recombination nodules form to mediate genetic exchange.
🧠 Did You Know?
In later stages, chiasmata become visible as remnants of crossing-over during diplotene and are seen until metaphase I.
💡 NCERT Memory Line:
Crossing over and recombination nodules occur during pachytene of prophase I.
Given below are two statements: Statement I: During Go phase of cell cycle the cell is metabolically inactive. Statement II: The centrosome undergoes duplication during S phase of interphase.
In the light of the above statements, choose the most appropriate answer from the option below:
AI-generated explanation. Check against your textbook.
Explanation:
Statement I is incorrect: during the G0 (Go) phase, cells are not actively dividing but remain metabolically active and can perform essential cellular functions. Statement II is correct: centrosome duplication occurs during the S phase of interphase, ensuring each daughter cell has a pair of centrosomes for bipolar spindle formation in mitosis. Therefore the right choice is 1: I is incorrect, II is correct.
🧠 Did You Know?
NCERT notes that cells in G0 are metabolically active but not progressing through the cell cycle, while S phase is when DNA replication and some organelle duplications (like centrosomes) occur.
💡 NCERT Memory Line:
Go phase: metabolically active, no division. S phase: centrosome duplication occurs.
Select the correct statements
A.Tetrad formation is seen during leptotene.
B.During Anaphase, the centromere split and chromatids separate.
C.Terminalization takes place during Pachytene.
D.Nucleolus, Golgi complex and ER are reformed during Telophase.
E.Crossing over takes place between sister chromatids of homologous.
Choose the correct answer from the option given below:
Select the incorrect statement with reference to mitosis:
AI-generated explanation. Check against your textbook.
Explanation:
Option 2 is incorrect. In mitosis, spindle fibers attach to kinetochores, which are protein structures at the centromere region of each chromosome. The attachment is to the kinetochore, not directly to the centromere as a general area. The NCERT description emphasizes kinetochores at the centromere for spindle attachment. The other statements are correct: during metaphase chromosomes align at the equator (1); during anaphase sister chromatids separate at the centromeres and move to opposite poles (4); and chromosomes decondense during telophase (3).
🧠 Did You Know?
Kinetochores are protein structures assembled at the centromere; spindle fibers connect to them to pull chromatids apart.
💡 NCERT Memory Line:
“Spindle fibers attach to kinetochores at the centromere to separate chromatids during mitosis.”