CBSE Questions for Class 11 Medical Biology Cell Cycle And Cell Division Quiz 7 - MCQExams.com

• Meiosis is a reductional division that leads to the production of haploid cells. 
• The chromosomal segments are exchanged during the crossing over which is the main cause of variation. 
• All the four chromatids of a homologous pair of chromosomes segregate and go over separately to four different daughter cells.
• This leads to variation in the daughter cells genetically.
  
  So, the correct answer is 'Both A and B'

Meiosis is important because it ensures that all organisms produced via sexual reproduction contain the correct number of chromosomes. Meiosis also produces genetic variation by way of the process of recombination. During prophase of meiosis I, the double-chromatid homologous pairs of chromosomes cross over with each other and often exchange chromosome segments. This recombination creates genetic diversity by allowing genes from each parent to intermix, resulting in chromosomes with a different genetic complement.Because of recombination and independent assortment in meiosis, each gamete contains a different set of  DNA. This produces a unique combination of genes resulting in zygote.

So,the correct option is 'D'.

Meiosis is a reductional cell division. It mainly takes place in the reproductive cell and reduces the chromosome number by half. This process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including animals, plants, and fungi. Meiosis begins with a parent cell that is diploid, which means it has two copies of each chromosome. The parent cell then undergoes one round of DNA replication which is followed by two separate cycles of nuclear division. The process results in four daughter cells that are haploid, which means they contain half the number of chromosomes of the diploid parent cell. So, the correct answer is option D.

Correct Option: B

Explanation:

1. Chromosomal crossing over is the exchange of genetic material between homologous chromosomes resulting in recombinant chromosomes.
2. The chromosomes segregate during Meiosis I which is made up of prophase I, Metaphase I, Anaphase I, and Telophase I.
   Prophase I is further differentiated into 5 stages- Leptotene, Zygotene, 
3. Prophase I is further differentiated into 5 stages- Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis. 
4. During the Pachytene phase of Prophase I homologous chromosomes pair up and become attached to one another.
5. At this time, crossing over takes place which involves the movement of sections of DNA between the non-sister chromatids of homologous chromosomes and allows for independent assortment. 

Prophase is marked by condensation of chromatin fibers and presence of visible sister chromatids of each chromosome. Metaphase is marked by alignment of duplicated chromosomes on the equatorial plate. Anaphase is marked by splitting of centromere and contraction of spindle fibers which in turn move the sister chromatids towards the opposite poles. Telophase is marked by the presence of daughter chromatids at the opposite poles. Cytokinesis is the division of cytoplasm that takes place after karyokinesis. So, the correct answer is A.

• The cell cycle includes a series of events, that take place in a cell which leads to the duplication of DNA and division of cells to form two daughter cells. 
• During the interphase or the initial phase, the cells grow in size, the DNA starts to duplicate.
  
• After that mitotic phase will start which is again divided into subphases.
• During the prophase of mitosis, the nuclear membrane dissolves followed by metaphase, anaphase, and telophase respectively. After telophase, karyokinesis will be completed while cytokinesis starts.
• With the completion of cytokinesis parent cell will be divided into two daughter cells.

Correct Option: A

Explanation:

• Crossing over or chromosomal crossover is the exchange of genetic material between homologous chromosomes.
• This process takes place during prophase I, of Meiosis. This is the cause of variation.

Mitosis is the process of cell division wherein, the chromosomes in a cell gets separated to to form two identical cells with equal number of chromosomes. The process of mitosis goes through interphase, prophase, metaphase, Anaphase and telophase before entering cytokinesis. While the first phases are the preparatory phases of the chromosome thickening, the metaphase finds the chromosomes  lined in the center of the cell to be divided. During Anaphase, the chromosomes gets divided from the centeromere, thereby giving rise to equal number of chromosomes which tend to move up to the two poles of the cell. During telophase, the chromosomes would have reached the two poles or ends of the cell and is ready for the division of the nucleoplasm. Hence, during the anaphase and telophase, the cell with 54 chromosomes will double the number of chromosomes i.e., 108. So, the correct answer is option A.

• The two replicated homologous chromosomes associate to form a bivalent.
• It is also known as tetrad and mainly formed during the pachytene stage of the meiosis.
• It consists of a pair of homologous chromosome, each with 2 sister chromatids (total of 4 chromatids) attached with one centromere (total of 2 centromeres)
• They undergo chiasmata formation for recombination.
  
  

• The gametes are produced by meiotic division. In meiosis 1, there is duplication and separation of the chromosomes in two cells. In meiosis II, there is a separation of the chromatids from the chromosomes and then the distribution occurs in the cells. There are four haploid gametes produced from one parent cell. The parent cell has two alleles for each gene. Each gamete contains only one allele from the parent.
• During the anaphase, the chromatids which are formed after the duplication of the chromosomes gets separated. There is the breaking of the chromosomes from the centromere. This is called as the chromosome split. These separated chromosomes then migrate to the opposite poles.

• Meiosis is also known as a reductional division. It results in a reduction of the diploid number of chromosomes to haploid. It mainly takes place in reproductive cells. 
• It produces genetic variability due to genetic recombination and independent assortment during meiosis. 
• It maintains the constancy in the number of diploid chromosomes during sexual reproduction across generations by meiosis II which is an equational division.

• Cytokinesis is the process in which the cytoplasm of a single cell divides to form two daughter cells. 
  
• Animal cells perform this by forming a cleavage furrow while plant cells construct a cell plate down the middle of the cell.