User:Waleedparas

Cell cycle is a series of events in which cell divides it self. And it is impossible to reverse this process in this process there are some phases -G1 -S -G2 -M G1:In g1 phase cell increases its size and increase its protein supply duplication of organelles  takes place in this phase. enzymes synthesis and synthesis of histone and tubulin protein which is essential for Mitotic phase. S:S phase is also called synthesis phase in this phase cell duplicates DNA and synthesis of RNA takes place. Making of chromosomes and duplication of chromosomes also takes place in this phase like one two chromatid of chromosomes becomes 4 chromatid latter it becomes two chromosomes with 2 DNA and 2000 nucleotides. G2:In this phase more growth of proteins and Spindle fiber and microtubules formation. this is the shortest phase of cell cycle. These all are inter phase now its turn of M phase '''M' 'This is Mitotic phase and it is also called divisional phase there are two types of cell division Mitosis meiosis

Mitosis: Mitosis is a type of cell division .It only occur in somatic cell it is for body development and for regenerate the body parts. In mitosis there are also some processes karyokinesis: Karyokinesis is a process in which nucleus divides. cytokinesis: Cytokinesis is a process in which cell divides. In '''Karyokinesis' 'these are some sub-phases, Pro-phase Meta-phase Ana-phase Telo-phase

1.Pro-phase:In this phase chromatin material condenses nuclear membrane disappears nucleolus disappear. The organelles present inside the nucleus spread all over the cell and the movement of spindle fibers towards its pole The diagram is below

2.Meta-phase:After prophase in metaphase meta-phase plate(arrangement of chromosomes in a line between the cell) spindle fiber movement towards centromere of chromosomes from two opposite poles from centrioles

3.Ana-phase:In this phase two Chromatids of chromosomes moves towards opposite poles due to force of attraction of centriole towards its pole now cell division 80% completed.

4.Telo-phase:This phase is inverse of prophase. In this phase nuclear membrane appears ,nucleolus appears now there are two nucleolus present on two opposite poles of cell. Chromosomes condenses. Now cell divides 98%. Now Karyokinesis. In karyokinesis bubbles formation between two nucleus and then cell membrane forms and gradually cell divides. These are major events of mitosis. Now its turn of meiosis Meiosis: Meiosis is a type cell division in which cell divides with half number of chromosomes. Meiosis occur in germ cell. It is essential for continuity of life.it has diploid no of chromosomes. There are two types of meiosis:
 * meiosis 1
 * meiosis 2

meiosis 1: In meiosis one there are 4 phases:
 * Pro-phase
 * Meta-phase
 * Ana-phase
 * Telo-phase

prophase of meiosis 1: In prophase of meiosis 1 condensation of chromosomes that chromosomes become visible then nuclear membrane disappears, nucleolus disappears pairing 2 of homologous chromosomes(chromosomes contains two chromatids)then chiasmata formation means crossing over of two non-sister homologous chromosomes then during chiasmata genes between two chromosomes that the genes of father and mother will be present in the sons cell. The organelles inside the nucleus spread all over the cell. Movement of centriole towards the opposite poles.

Meta-phase: After Prophase in metaphase meta-phase plate formation that the spindle fibers cross between the centromere of chromosomes.

Anaphase: In Anaphase due to force of attraction of spindle fibers toward opposite poles chromosomes become half and two two chromatid moves towards opposite poles.

Telo-phase In Telophase nuclear membrane appears nucleolus appears chromosomes condenses now there are two nucleus on opposite poles of cell. Now in karyokinesis bubbles forms between nucleuses and cell divides.

Meiosis 2: it is similar to mitosis which I have written above.