CBSE Questions for Class 11 Medical Biology Cell Cycle And Cell Division Quiz 9 - MCQExams.com

 Meiosis is a special type of cell division a process where a single cell divides two times to produce four haploid cells, each not only containing half the original amount of genetic information but also genetically distinct from the parent cell that gave rise to them. This process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including animals, plants and fungi.

For the first time, meiosis was discovered and described by Oscar Hertwig, a German biologist, in 1876, in sea urchin eggs. Then again in 1883, it was described by Edouard van Beneden in roundworms. A German biologist, August Weismann in 1890, described the significance of meiosis for reproduction and inheritance. The term "meiosis" was introduced by J.B. Farmer and J.E.S. Moore in the year 1905. Thus, the correct answer is option A. 

• In prophase, the complex of DNA and histone proteins around which DNA is wrapped contained in the nucleus, known as chromatin, condense resulting in the formation of visible chromosomes.
• Simultaneously, the nucleolus disappears and the nuclear envelope breaks down.
  
• During interphase, the cell grows and the nuclear DNA is duplicated. It is followed by the mitotic phase. 
  
• During metaphase, the chromosomes align themselves in the middle of the cell forming a metaphasic plate.
  
• During telophase, a nuclear membrane forms around each set of chromosomes to separate the nuclear DNA from the cytoplasm.
  

• In telophase, the chromosomes decondense no individual chromosome can be seen. 
• The chromosomes aggregate at opposite poles and their identity is lost as discrete elements.
• The nuclear envelope assembles around the chromosome clusters.
• Nucleolus, golgi complex, and ER reforms.
• So, the correct answer is option C.

• In mitosis division, the centromere of each chromosome divides into two so that each chromatid has its centromere. 
• The two chromatids begin repelling each other and separate completely to become the daughter chromosome. 
• The daughter chromosome move towards the poles of the spindle along with the path of their chromosome fibre. 
• In anaphase, the movement of chromosome the centromeres lead the path and form different shapes of chromosomes are V, J, L, I shaped chromosomes. 
• So, the correct answer is option C.

• The nuclear envelope reformed in telophase of M-phase. During cell division, the division of the protoplast of a cell into two daughter cells after nuclear division takes place in cytokinesis. 
• In plant cells, cytokinesis takes place by two methods, i.e., cleavage and cell-plate method. 
• In the cell-plate method, the central part of the spindle grows in size and forms a complex called phragmoplast. The phragmoplast reaches the equator and fused to form a cell plate. This cell plate later forms the primary wall and both the cell separate out. 
• In animal cells, during cytokinesis, the contractile ring is formed which is composed of filamentous actin and the motor protein, and some additional proteins. 

• During prophase I of meiosis, homologous chromosomes combine and type synapses, a step distinctive to meiosis. 
• The bivalents are the paired chromosomes and so the creation of chiasmata reasoned by genetic recombination becomes apparent.
• Chromosomal condensation permits these to be viewed beneath the magnifier. 
• Hence, The given diagram represents meiosis Prophase I.

• Anaphase is characterized by two distinct motions. The first of these, anaphase A, moves chromosomes to either pole of a dividing cell (marked by centrosomes, from which mitotic microtubules are generated and organised). The movement for this is primarily generated by the action of kinetochores, and a subclass of microtubule called kinetochore microtubules.

• The second motion, anaphase B, involves the separation of these poles from each other. The movement for this is primarily generated by the action of interpolar microtubules and astral microtubules.

Correct Option: D

Explanation:

• Meiosis is a process where the single cell divides twice to produce four cells.

• It produces half the amount of genetic information from parental chromosomes. 

• There are two cell phases which are meiosis I and meiosis II.

• meiosis I, considered as reductional division, and the number of chromosomes is halved.

hence, in meiosis I, the number of chromosomes is halved.

• Each parental cell produces two daughter cells after a mitotic division. By using, 2n we can find out the number of mitotic divisions.
  
• Here, n is the number of mitotic divisions
• 2$$^n$$ = 1024
• $$n$$ = 10
• So, the correct answer is option B.

•  During pachytene, the homologous chromosomes thicken and become recombinant. Crossing over of segments of genetic information occurs between non-sister chromatids of homologous chromosomes, forming exchange sites called chiasmata and resulting in recombination
• During metaphase, the kinetochore microtubules pull the sister chromatids back and forth until they align along the equator of the cell, called the equatorial plate.
• Diakinesis. the final stage in the first meiotic prophase in gametogenesis, in which the chromosomes achieve their maximum thickness. The chiasmata and nucleolus disappear, the nuclear membrane degenerates, and the spindle fibres form in preparation for the formation of dyads.
•  Zygotene is the sub-stage where synapsis between homologous chromosomes begins. It is also known as zygonema. These synapsis can form up and down the chromosomes allowing numerous points of contact called 'synaptonemal complex', this can be compared to a zipper structure, due to the coils of chromatin.