Ten-Sentence Overview of CB-03

1. The cell cycle consists of interphase (G1 → S → G2, ~95% of duration) and the M phase (mitosis + cytokinesis, ~5%), with some cells exiting to G0 quiescence.

2. During S phase, DNA replication doubles DNA content from 2C to 4C, but the chromosome number remains 2n because sister chromatids are joined at the centromere — the most important trap in NEET cell biology.

3. G2 phase involves tubulin synthesis for the mitotic spindle; DNA content remains 4C until cytokinesis divides it equally.

4. Mitosis (equational division) proceeds through PMAT stages, producing two genetically identical diploid daughter cells used for growth, repair, and asexual reproduction.

5. Anaphase of mitosis is characterised by centromere splitting and separation of sister chromatids; in plant cells cytokinesis occurs by centrifugal cell plate formation from Golgi vesicles, while animal cells use a centripetal cleavage furrow.

6. Meiosis involves two divisions (I and II) producing four haploid gametes with 1C DNA content from one diploid cell with 4C DNA.

7. Prophase I is meiosis's unique and longest stage, subdivided into LZPDD: Leptotene (condensation), Zygotene $\frac{synapsis}{bivalent formation}$, Pachytene (crossing over), Diplotene (chiasmata visible), Diakinesis (terminalization, nuclear envelope breakdown).

8. Crossing over in pachytene exchanges segments between non-sister chromatids of homologous chromosomes; chiasmata only become visible in diplotene when the synaptonemal complex dissolves — these are different substages.

9. Anaphase I separates homologous chromosomes (NOT sister chromatids), making it the reductional step — centromeres do not split in meiosis I, only in meiosis II and mitosis.

10. Meiosis generates genetic diversity through crossing over (recombination within chromosomes) and independent assortment (random orientation of bivalents at metaphase I), both essential for evolution and species variation.