Question

4. Describe the stages of the cell cycle and what happens in each stage, making sure to include what is happening to the DNA. For M phase, describe all stages. If you were looking at cells under the microscope, what would you use as a distinguishing feature for each stage. Only for this last part on looking at cells under a microscope can you make a table, if you wish.

5. Describe what “Alternation of Generation” means and describe in detail the human alternation of generation. Make sure to include each of the following terms: haploid, diploid, homologous chromosomes, mitosis, meiosis, somatic cell, germ cell, zygote.

Answer 1

4)- cell cycle comprises Interphase and M- phase(division phase).

Interphase- it is the most active phase of cell cycle. During Interphase cell grow in size and prepare itself for next division. Interphase completed in to following three stages.

G1- phase ( growth phase 1 )- most of the protiens and enzyme synthesized for DNA replication and cell growth maximum in this phase.

S-phase (synthesis phase) - DNA and histone protein are Synthesized. Amount of DNA per Cell becomes double but chromosome number remain constant.

G2- phase (growth phase 2) - this is the last phase of Interphase in which cell grow some more and cell becomes all most ready for division.

M-phase (division phase)- phase of actual cell division and consist of following 4 sub stages.

Prophase- chromatin begin to condensed and spindle formation starts. Nuclear membrane, nucleolus, Endoplasmic reticulum and Golgi complex are disappear.

Metaphase- spindle formation completed and all the chromosomes lies at equator i.e metaphasic plate forms. Spindles are attached to kinetochore of chromosome at one hand and the pole on other hand.

Anaphase- all the centromere of all chromosome are split simultaneously and spindle contract due to which both set of doughter chromosomes moves toward opposite pole.

Telophase- chromosomes reached their respective Poles.spindle fibre has disappeared and Nuclear membrane, nucleolus, Golgi complex and Endoplasmic reticulum are reappear.

Prophase , Metaphase, Anaphase and telophase are the part of Nuclear division (karyokinesis).

After karyokinesis, both doughter cells completely separated to each other by Cytokinesis i.e division of cell cytoplasm. In animal cell , Cytokinesis takes place by constriction and forrow formation (from out side to in side).