Cell Cycle and Cell Division Test - 41

The meiosis division is the reduction division. During the Metaphase stage of meiosis, the chromosomes of the parent cell are lined at the equatorial region. Following the formation of Spindle fibers, the chromosomes are divided into equal numbers and move to the two poles and two daughter cells are formed These daughter cells which form the gametes have half the number of chromosomes of their  parent cell. So, the correct answer is option D.

The maximum time taken by the cell in in G1 phase, which is around 10 hours, This is followed by S phase, for around 9 hours, followed by G2 phase, 4 hours and then mitosis and cytokinesis, which is 1 hour and less than 1 hour respectively.

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 G$$_1$$ phase is the gap between M phase and S phase and is marked by synthesis of RNA and protein (excluding histones) and duplication of all cell content except DNA. 
• S phase of DNA replication is followed by G$$_2$$ phase during which cell double-checks the duplicated DNA content. 
• The M phase of cell cycle is marked by the division of the nucleus and cytokinesis to produce daughter cells. G$$_0$$ phase is the quiescent stage. 

Nondisjunction is the failure of separation of sister chromatids or homologous chromosomes during anaphase. Disjunction is the separation of sister chromatids during anaphase. Crossing over is an exchange of genetic material between non-sister chromatids of the homologous pair. Mutation refers to sudden changes in genetic material. Exchange of chromosomal segment between two non-homologous chromosomes is called translocation. So, the correct answer is B.

From the observation of the above given diagram, the sister chromatids are not separated which results in the abnormal distribution of the chromosomes in the daughter nuclei (as can be seen in the gametes). This phenomenon is called non-disjunction. 

Crossing over is the process of exchange of genetic material between non-sister chromatids of homologous chromosomes and produces new genetics combinations or variations. It does not confer health advantages or does not increase the number of gametes. A number of chromosomes are halved in gametes due to the separation of homologous chromosomes and their movement to opposite poles during anaphase I. 

The process of cell division in somatic cells is known as mitosis. This division takes place in five stages prophase, metaphase, anaphase, telophase, and cytokinesis. All through these stages, the main changes take place in the chromosomes which transform from the threadlike chromatin network to chromatids to thickened chromosomes. Finally, during telophase, the  daughter chromatids which have moved towards the poles and form a network slowly start uncoiling and this is followed by the formation of the nuclear membrane that as it deepens divides these parent cell into two daughter cells.