Cell cycle, mitosis, meiosis
- The correct sequence of phases of cell cycle is : Answer: 4. G ₁ → S → G ₂ → M The cell cycle runs G₁ → S → G₂ → M . G₁ is growth, S is DNA synthesis, G₂ is preparation for division, and M i... 1
- The stage during which separation of the paired homologous chromosomes begins is Answer: 3. Diplotene In prophase I, homologous chromosomes start to separate at diplotene, held together at chiasmata. Zygotene is pairing (... 1
- Which of the following options gives the correct sequence of events during mitosis ? Answer: 1. condensation → nuclear membrane disassembly → arrangement at equator → centromere division → segregation → telophase The correct... 1
- 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 ? Answer: 2. Chromosomes will not segregate Key idea: APC degrades securin so that separase can cut cohesin between sister chromatids at the m... 1
- When cell has stalled DNA replication fork, which checkpoint should be predominantly activated? Answer: 1. G ₂ /M A stalled replication fork means DNA is not fully replicated. The cell must delay entry into mitosis until replication and... 1
- Match the stages of meiosis in Column—I to their characteristic features in Column—II and select the correct option using the codes given below :Column—I: a. Pachytene; b. Metaphase I; c. Diakinesis; d. ZygoteneColumn—II: (i) Pairing of homologous ch… Answer: 4. (iii) (iv) (ii) (i) Each stage of meiotic prophase I has one signature event. Pachytene: crossing-over between non-sister chromat... 1
- During cell growth, DNA synthesis takes place in Answer: 4. S phase In the cell cycle, DNA replication happens in the S (synthesis) phase of interphase. G₁ is for cell growth and preparing... 1
- Which of the following is not a characteristic feature during mitosis in somatic cells ? Answer: 4. Synapsis Synapsis (pairing of homologous chromosomes) occurs in prophase I (zygotene) of meiosis, not in mitosis. Spindle fibres,... 1
- A cell at telophase stage is observed by a student in a plant brought from the field. He tells his teacher that this cell is not like other cells at telophase stage. There is no formation of cell plate and thus the cell is containing more number of c… Answer: 2. Polyploidy Failure of cell plate formation in telophase (cytokinesis fails) leaves a cell with a doubled chromosome number. Cells... 1
- Spindle fibres attach on to : Answer: 2. Kinetochore of the chromosome Key idea: Spindle fibres attach to the kinetochore. The kinetochore is a disc-shaped protein struct... 1
- In meiosis crossing over is initiated at : Answer: 1. Pachytene Key idea: Crossing over takes place at pachytene. At pachytene (prophase I), recombination nodules form and the enzyme... 1