Cell Cycle and Cell Division Test - 69

DNA is replicated during the S phase of a cell cycle. So, during the metaphase stage, each chromosome (i.e., each chromatid pair) will contain two molecules of double-stranded DNA (one molecule per sister chromatid) in mitosis. 

Gametes (egg, sperm. pollen, etc.) only have half the amount of DNA as normal cells in the organism. 

The synthesis of the daughter DNA from the template DNA or the replication of DNA starts and ends in the S-Phase (synthesis phase) of the interphase.

Mitosis is a process of cell division, whereby a single cell divides into two genetically identical daughter cells. The five stages of mitosis s interphase, prophase, metaphase, anaphase, and telophase. Almost 80 percent of a cell's lifespan is spent in the interphase stage of mitosis. During this stage, no division takes place, but the cell undergoes a period of growth and prepares itself for the division. Cells contain many proteins and structures called organelles that must replicate in preparation for doubling. The DNA of the cell duplicates during this phase, creating two copies of each strand of DNA called a chromosome. A chromosome is a DNA molecule that carries all or part of the hereditary information of an organism. Interphase itself is split into different phases: G1 phase, S phase, and G2 phase. G1 phase is the period prior to the synthesis of DNA, during which the cell increases in size. During the G1 phases, cells grow and monitor their environment to determine whether they should initiate another round of cell division. During the narrow S phase, DNA is synthesized. This is followed by the G2 phase when the cell synthesizes proteins and continues to get bigger. During the G2 phase, cells check to make sure DNA replication has successfully completed, and make any necessary repairs.

A cell divides to form 128 cells. That means it divided 127 times. Hence 127 spindles will be produced.

• 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 ".

• The fibres that are formed in between the centromeres of the homologous chromosomes are interzonal fibres. 
• Chromosomes are lined up on the equator of shaft in Metaphase. These are then separated into a frame of appendages with different shapes in Anaphase. 
• Thus, Interzonal fibres is seen between Metaphase to Anaphase. Option B is correct.

8 male gametes are produced from 1 spore mother cell.

The cell cycle is the series of events that lead to the doubling of DNA of a cell and the formation of two daughter cells. It is divided into four phases- G1, S, G2, and M phase. In the S phase DNA content is doubled.

• Interphase is the phase of the cell cycle in which the cells spend most of its life. The cells obtain nutrients and perform normal functions.
•  This phase is also known as resting phase. The nucleolus is a dark, spherical dense granular mass of the resting nucleus. 
• The nucleosome is found in the interphase nucleus consisting of DNA coiled around a core of histones. 
• A chromatid is found in the interphase nucleus which is one-half of two identical copies of a replicated chromosome.