Cell Cycle and Cell Division Test - 58

• Cyclin-dependent kinases, through phosphorylation,  signal the cell that it is ready to pass into the next stage of the cell cycle. As their name suggests, Cyclin-Dependent Protein Kinases are dependent on cyclins, another class of regulatory proteins. Cyclins bind to Cdks, activating the Cdks to phosphorylate other molecules.

So, the correct option is 'cyclin'.

Unlike in the plant and animal cells where both mitosis and meiosis can be seen, the bacterial cells do not divide through mitosis or meiosis. They divide through a process called binary fission. The binary fission process though appear to be similar to the mitosis seen in the somatic cells of plants and animals, there are some differences; like the absence of spindle fibres and the absence of a gap between the 's" Phase and the 'M' Phase that can be seen in the mitosis process. Thus, the correct answer is option C.

The cell cycle consists of two basic phases, a long non-dividing interphase phase, and a short dividing M phase. In the average duration of 24 hours in the cell cycle of dividing human cell, M phase lasts for one hour (less than 5% of total) while interphase phase or interphase occupies 75−95% of total generation time.

Haploid cells are formed from meiosis. First of all, interphase happens where the cell spends most of its life. After following G1, S and G2 phase, the cell enters prophase 1, where homologous chromosomes condense and pair up to form a tetrad. At this stage, crossing over happens to allow the exchange of genetic materials.

• Meiosis is the reduction division where the cell after dividing produces 4 daughter cells each having half the genetic material compared to the mother cell.
• This kind of division takes place in the formation of the gametes which are required for reproduction.
• The gametes are haploid as in sexual reproduction 2 type of gametes are required where both are haploid and when they fuse they form a diploid zygote.
• Sexual reproduction is important from the evolutionary point of view as the during the formation of the zygote the gametes from both the parents are fused and the zygote will acquire the characteristics of both the parents .
• Thus the offspring will have characters from both the parents as well new characters may be formed because of both the genetic material coming together.
  
• Also during meiosis 1 in the prophase the chromosomes go under the process of crossing over where the genetic material between the non sister chromatids is exchanged this provides for the chances of genetic recombination thus forming variation in the genetic material.
• Therefore the answer option 'Genetic recombinations are possible' is correct.
  

• During the leptotene stage of the prophase 1 of the meiosis 1 the chromosomes are condensed and they start to form pairs.
• The homologous chromosomes that pair are called sister chromatids.
• Each pair of chromosomes have 2 chromosomes which are similar to each other. They are connected to each other by the means of centromere which is present in the middle of the chromosomes and are also called primary constriction.
• Bivalents mean that structure has 2 pairs of homologous chromosomes. Which means that each pair has 2 sister chromatids which is each connected by a centromere.
• Therefore the whole structure is made up of 4 chromatids ( 2 pair of sister chromatids) and 2 centromere each present in 1 pair.
• Therefore the correct answer is option 'four chromatids and two centromere'.

Prophase is the first phase of both mitosis and meiosis. Beginning after interphase, DNA has already been replicated when the cell enters prophase .so chromosomes are in the duplicated state during prophase. It is the process that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells. During prophase, the complex of DNA and proteins contained in the nucleus, known as chromatin, condenses. 

So, the correct answer is 'C'

• The Cell cycle is divided into 2 phases the  M phase and the interphase. 
• The Mphase is where the actual cell division takes place, while interphase is the one where the cell rests and grows between the 2 consecutive cell division. 
• The interphase is divided into G1, S and G2 phase where the G1 phase takes place after the cell division here the cells rest before it starts for the next cell division. 

• The DNA that was replicated during the Sphase of the interphase are held together by the centromere till the chromosome are detached from each other to be pulled towards the poles of the dividing cells.
• Metaphase is the second phase of the mitosis where the chromosomes after the condensation and disappearance of the nuclear membrane are lined at the metaphase or the equatorial plate in the middle of the dividing cell
• At the end of the metaphase the spindle fibers from the centrioles are attached to the kinetochore which are present beside the centromere in the middle of the chromosome.
• So when the chromosomes are pulled towards the poles in the anaphase the centromere are not required to hold the chromosomes together and so the centromere are also divided but at the end of the metaphase where the chromosomes are ready to be pulled towards the pole of the dividing cells.
• Therefore the correct answer is option 'holds the replicated DNA molecules together'.