CBSE Questions for Class 11 Medical Biology Cell Cycle And Cell Division Quiz 12 - MCQExams.com

1. Meiosis is the reductional division wherein the cell undergoes division twice.
2. Diploid cell(2n)  divides further into haploid cells(n). 
3. In meiosis, each cell receives only one set of chromosomes. These cells are called gametes.
4. Thus during zygote formation haploid male and haploid female gamete fuse to form a diploid zygote.
5. Thus meiosis the an important process for formation of gametes to perform sexual reproduction. 

A single mitotic division of one cell produces two cells. 2nd division of this two cells produces 4 cells and so on.

$$ 2^n$$ = number Of cells after n divisions. Thus 7 generations of mitosis yield 128 cells from a single cell.

So the answer is '7'. 

• Diakinesis is the last stage of the prophase of meiosis. Homologous chromosomes are attached for recombination at points called chiasmata. These move towards the edges in diakinesis. This is termes as Terminalisation.
  
• S phase is the synthesis stage of interphase. Here, the DNA is replicated, histones, proteins, and other required materials are being synthesized. 
  
• Pulling apart of homologous chromosomes or sister chromatids is called disjunction and happens at anaphase of meiosis.
  

Formation of four unidentical daughter cells from a parent cell is called Meiosis or reductional division. In plants, it occurs in diploid spore mother cells and in animal cells, it occurs in diploid germinal cells.

All nuclear changes (Prophase, metaphase, anaphase, and telophase) that occurs during mitotic cell division are collectively called as karyokinesis. Mitotic cell division consists of two steps. The first step is karyokinesis where nuclear division takes place which is followed by cytokinesis i.e the division of cytoplasm takes place and individual daughter cells are formed. So, the correct answer is 'Karyokinesis'.

• Karyokinesis is the process of division of the nucleus of a cell during cell division i.e mitosis or meiosis.
• It has following phases-

• Pachytene is the third stage of prophase 1 of meiosis.
• During this stage, each chromosome pair separates into sister chromatids and crossing over of genes occurs.
  
• Crossing over is also called synapsis and is is one of the final stages of genetic recombination.
  
• It is the process of exchange of genetic materials or segments between non-sister chromatids of homologous chromosomes.
  
• So, the correct answer is 'Two homologous chromosomes'.

$$\textbf{Correct option:C}$$ 

$$\textbf{Solution:}$$

$$\bullet$$ Meiosis is also known as reductional division which is a double division that occurs in a diploid cell to give rise to four haploid cells called each having half the number of chromosomes as compared to the parent cell.

$$\bullet$$ If the haploid cell has 20(n) chromosomes then the mother cell will have 40 (2n) chromosomes.

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

• 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.  

1. In Prophase, nuclear envelope degenerates and chromosome condenses.
2. Metaphase is the stage where chromatids align themselves at the equatorial/metaphase plate.
3. Anaphase is marked by splitting of centromeres followed by pulling of sister chromatids of each chromosome towards the opposite poles.
4. Telophase is marked by sister chromatids reaching the opposite poles and the reformation of nuclear vesicles around it.

• Chromatin gets condensed into thick chromosomes during the prophase stage.
• During zygotene stage of prophase I, pairing of homologous chromosomes takes place and a bivalent structure or tetrad is formed.
  
• During pachytene stage of prophase I, crossing over occurs between non-sister chromatids of homologous chromosomes in which a part of chromatids is exchanged. This is called recombination and leads to the formation of synaptonemal complex.
• During diplotene stage of prophase I, dissolution of synaptonemal complex occurs. The chromosomes begin to repel each other except in the place of cross over and this leads to the formation of a X shaped structure called chiasmata.

• DNA replication occurs once only before gap-2 i.e. S-phase or synthesis phase.
• Karyokinesis occurs once in mitosis and twice in meiosis.
  
• Reduction of ploidy occurs at Anaphase-1.
• Crossing over in tetrad stage.
• So,the correct option is " Reduction of ploidy at metaphase -1 ".