CBSE Questions for Class 11 Medical Biology Cell Cycle And Cell Division Quiz 14 - MCQExams.com

• In mitosis, each cell divides into two. So starting from a single cell, the increase in a number of cells will occur as per the following progression- 1->2->4->8->16->32->64->128.
  
  
• Thus a total of 7 divisions is required to produce 128 cells starting from a single cell or 2$$^n$$ times the division.

• Cell cycle is the series of events that occurs to a cell, at the end of which it converts into two daughter cells. It composed of Interphase, division phase (mitosis/meiosis), and cytokinesis.
• Cell division is the splitting of one cell into two daughter cells.
• Karyokinesis is the process of division of the nucleus.
• Kinesis is the movement or activity of a cell in response to some stimuli.

$$\textbf{Correct option:A}$$ 

$\textbf{Solution:}$$

$$\textbf{Option (A)}$$

$$\bullet$$Leptotene stage is the first step of meiotic division-I,which is also known as bouquet stage ,chromosome become gradually visible ,nuclear membrane initiates to disappear.

$$\textbf{Option (B)}$$

$$\bullet$$ Synapse occurs in the zygotene phase of meiosis I where the homologous chromosomes get attached to each other by means of a nucleoprotein known as synaptonemal protein ,this protein is present in between the chromatids also .The linkage is such that all the genes expressing the same characters falls against each other.

$$\textbf{Option (C)}$$

$$\bullet$$ Terminalisation is the phenomenon of chiasmata shifting towards the ends of the chromosomes that takes place in the diakinesis stage of meiosis I, nucleolus, nuclear envelope finally degenerates.

$$\textbf{Option (D)}$$

$$\bullet$$ Crossing over is the process of exchange of genetic material between two non sister chromatids that takes place in the pachytene stage.

$$\bullet$$ At the pachytene stage, the two homologous chromosomes start condensing and shorten in size such that all the chromatids present in each chromosome become more distinct and these look like four chromatids and it is known as tetrad.

$$\textbf{Hence, the correct option is (A)}$$

• DNA replication occurs during the synthesis or S phase. 
• Non-proliferative cells in multicellular eukaryotes generally enter the quiescent $$G_{0}$$ state from $$G_{1}$$and may remain quiescent for long periods of time, possibly indefinitely (as in the case of neurons). Thus, $$G_{0}$$ is also called a differential stage. 
• Tubulin proteins are used in spindle formation and synthesized in G$$_{2}$$ phase. 
• The events of the cell cycle are tightly regulated. Two key classes of regulatory molecules, cyclins and cyclin-dependent kinases (CDKs), determine a cell's progress through the cell cycle. Cyclin D binds to existing CDK4, forming the active cyclin D-CDK4 complex during $$G_1$$ phase, so that cell can successfully enter $$S$$ phase.

Correct Option: C

Explanation:

• In bivalent condition, there are two chromosomes present with their homologous pair.
• So, 8 bivalents in metaphase I contains 16 chromosomes.
• Meiosis I is a reduction division and therefore the number of chromosomes is halved to 8 chromosomes.
• Meiosis II is an equational division and therefore the number of chromosomes remains same, that is, 8 chromosomes.

Hence, if the number of bivalents is 8 in metaphase I, the number of chromosomes in daughter cells after meiosis I and meiosis II respectively will be 8 and 8.