NCERT-NEET-Growth and reproduction are characteristics of cells,indeed of all living organisms. All cells reproduce by dividing into two,with each parental cell giving rise to two daughter cells each time they divide. These newly formed daughter cells can themselves grow and divide,giving rise to a new cell population that is formed by the growth anddivision of a single parental cell and its progeny. In other words, such cycles of growth and division allow a single cell to form a structure consisting of millions of cells

Enter OTP to View Content

Stage	Characteristics
G1 Phase	Interval between mitosis and DNA replication initiation. Cell grows and carries out normal metabolism. Organelles are duplicated.
S Phase	DNA synthesis or replication occurs. DNA content doubles from 2C to 4C, but chromosome number remains the same (2n). Centriole duplicates in the cytoplasm in animal cells.
G2 Phase	Preparation for mitosis. Protein synthesis occurs. Cell growth continues.
M Phase	Period of actual cell division. Includes nuclear division (karyokinesis) and cytoplasmic division (cytokinesis).
Prophase	Chromosomal material condenses to form compact mitotic chromosomes. Chromosomes are composed of two chromatids attached at the centromere. Centrosomes move to opposite poles. Formation of mitotic spindle apparatus begins. Disintegration of nuclear envelope, nucleolus, golgi complexes, and endoplasmic reticulum.
Metaphase	Complete disintegration of the nuclear envelope. Chromosomes align at the equatorial plate (metaphase plate). Spindle fibers attach to kinetochores.
Anaphase	Centromeres split and chromatids separate. Chromatids move to opposite poles.
Telophase	Chromosomes reach the poles and decondense. Nuclear envelope reforms around chromosome clusters. Nucleolus, golgi complex, and ER reform.
Cytokinesis	Division of the cytoplasm to form two daughter cells. In animal cells, a furrow forms in the plasma membrane, deepens, and splits the cell. In plant cells, a cell plate forms, growing outward to meet existing cell walls.
G0 Phase	Cells remain metabolically active but do not proliferate unless required. Occurs in non-dividing cells like heart cells.
Prophase I	Long and complex compared to mitotic prophase. Subdivided into five stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis. Homologous chromosomes pair (synapsis), crossing over occurs, recombination of genetic material.
Leptotene	Chromosomes become visible. Chromosome compaction continues.
Zygotene	Homologous chromosomes start pairing. Synaptonemal complex forms. Chromosomes form bivalents or tetrads.
Pachytene	Chromosomes become tetrads (four chromatids). Crossing over occurs at recombination nodules. Recombination leads to genetic diversity.
Diplotene	Dissolution of the synaptonemal complex. Homologous chromosomes separate except at crossover sites (chiasmata).
Diakinesis	Terminalisation of chiasmata. Chromosomes are fully condensed. Spindle apparatus forms. Nuclear envelope and nucleolus disappear.
Metaphase I	Bivalents align on the equatorial plate. Microtubules from opposite poles attach to kinetochores of homologous chromosomes.
Anaphase I	Homologous chromosomes separate, moving to opposite poles. Sister chromatids remain attached at centromeres.
Telophase I	Nuclear membrane and nucleolus reappear. Cytokinesis follows, resulting in dyad of cells.
Interkinesis	Short phase between meiosis I and meiosis II. No DNA replication occurs.
Prophase II	Similar to mitotic prophase. Nuclear membrane disappears. Chromosomes condense.
Metaphase II	Chromosomes align at the equator. Microtubules from opposite poles attach to kinetochores of sister chromatids.
Anaphase II	Centromeres split. Sister chromatids separate and move to opposite poles.
Telophase II	Chromosomes decondense. Nuclear envelope reappears around chromosome clusters. Cytokinesis follows, resulting in four haploid daughter cells.