Chapter 10: CELL CYCLE & CELL DIVISIONUnit 3: Cell Structure and Function2-3 Questions Fix in NEET 2027

Hello NEET Aspirants! 👋

NEET Dropper here dropping Ch-10: Cell Cycle

Complete Notes + PYQ Tod + No Ratta Only Samajh 🧠

Mitosis = 2n → 2n, Meiosis = 2n → n

Anaphase I = Chromosome Jata, Anaphase II = Chromatid Jata

Prophase I = Lepto Zygote Pache Diplo Diakinesis

### *1. CELL CYCLE* `Basic = 1Q`  

*A. Definition + Phases*

Cell Cycle = Series of events = DNA Duplication + Cell Division

Average Duration: Human Cell = 24 hrs, Yeast = 90 min

*B. Two Main Phases* `Chart Pakka`

**Phase** **Duration** **Key Events** **NEET Point**

**Interphase** 95% Time = 23 hrs Cell Growth + DNA Replication **Resting Phase nahi hai**

**M Phase** 5% Time = 1 hr Actual Division = Mitosis/Meiosis Equational/Reductional

*C. Interphase - 3 Stages* `1Q Fix`

1. G1 Phase = Gap 1 = Interval = Growth = Proteins + Organelles + RNA

   Most Variable Duration = Decides Cell Cycle Length

2. S Phase = Synthesis = DNA Replication = 2C → 4C DNA but Chromosome No Same

   Centriole Duplicates in Animal Cell

3. G2 Phase = Gap 2 = Growth + Protein for Mitosis + Tubulin Synthesis

   Cell = 4C DNA

*G0 Phase* = Quiescent Stage = Cells Exit G1 = No Division = Neurons, Heart Cells  

*NEET Trap*: G0 me cell metabolically active hota, dead nahi.

### *2. MITOSIS* `Equational Division = 1Q`  

*A. Why Mitosis?*

1. Growth = Zygote → Adult

2. Repair = Skin Cells, Gut Lining

3. Asexual Reproduction = Amoeba

4. Maintains Chromosome No = 2n → 2n

5. Maintains Nucleo-Cytoplasmic Ratio

*B. Karyokinesis - 4 Stages* `Diagram + Sequence Q`

**Stage** **Key Events** **Diagram Label** **Trick**

**Prophase** 1. Chromatin → Chromosome Condensation

2. Centriole → Opposite Poles = Asters

3. Spindle Formation

4. Nucleolus + Nuclear Envelope Disappear Chromosome = 2 Chromatids + Centromere, Aster, Spindle Fibres **P** = **P**reparation

**Metaphase** 1. Chromosomes → Equator = Metaphasic Plate

2. Best Stage to Count Chromosomes

3. Kinetochore = Spindle Attach Site Metaphasic Plate, Kinetochore, Centromere at Equator **M** = **M**iddle

**Anaphase** 1. Centromere Splits = Sister Chromatids Separate

2. Chromatids → Opposite Poles

3. Shape = V, L, J, I based on Centromere Position Daughter Chromosomes Moving, V-Shaped = Metacentric **A** = **A**way

**Telophase** 1. Reverse of Prophase

2. Chromosomes → Chromatin

3. Nuclear Envelope + Nucleolus Reappear

4. Spindle Disappear 2 Daughter Nuclei Formed **T** = **T**wo Nuclei

*C. Cytokinesis* `Plant vs Animal`

Animal Cell = Cleavage = Furrow = Centripetal = Outside → Inside

Plant Cell = Cell Plate = Phragmoplast = Centrifugal = Inside → Outside

NEET Point: If Cytokinesis nahi hui = Syncytium = Multinucleate = Liquid Endosperm Coconut

### *3. MEIOSIS* `Reductional Division = 2Q Fix`  

*A. Why Meiosis?*

1. Gamete Formation = Sexual Reproduction

2. Reduces Chromosome No = 2n → n = Fertilization pe wapas 2n

3. Genetic Variation = Crossing Over + Independent Assortment

4. Occurs in: Diploid Germ Cells = Testis + Ovary

*B. Meiosis I - Reductional* `Prophase I = Most Important`  

*Prophase I - 5 Stages* `Sequence Q 100%`

1. Leptotene = Chromosomes Thin + Thread-like = Chromomeres Beads Visible

2. Zygotene = Pairing = Synapsis = Bivalent/Tetrad Formation = 2 Chromosome + 4 Chromatids

   Synaptonemal Complex = Protein Structure = Holds Homologous Pair

3. Pachytene = Crossing Over = Recombination Nodules = Non-Sister Chromatids Exchange

   Enzyme = Recombinase, Site = Chiasmata, Result = Genetic Variation

4. Diplotene = Synaptonemal Complex Dissolves = Chiasmata Visible = X Shape

   Oocytes = Arrested here = Dictyotene Stage = Birth se Puberty tak

5. Diakinesis = Terminalisation of Chiasmata = Chromosomes Fully Condensed

   Nucleolus + Nuclear Envelope Disappear

*Trick*: *L*adki *Z*iddi *P*akka *D*eewani *D*ikhayi = Lepto Zygote Pache Diplo Diakinesis

*Rest of Meiosis I*

Metaphase I = Bivalents at Equator = Homologous Pair = Independent Assortment

Anaphase I = Homologous Chromosomes Separate = NOT Chromatids = Reduction Happens

Telophase I = 2 Haploid Cells = n = Chromosome No Half, DNA Still 4C

Interkinesis = Gap between Meiosis I & II = No DNA Replication = Short

*C. Meiosis II - Equational = Mitosis Jaisi*

Prophase II = Chromosomes Condense

Metaphase II = Chromosomes at Equator = Single

Anaphase II = Sister Chromatids Separate = Centromere Splits

Telophase II = 4 Haploid Cells = n = DNA = 2C → 1C

Result: 1 Diploid Cell → 4 Haploid Gametes

### *4. MITOSIS vs MEIOSIS* `Table Q Pakka`

**Feature** **Mitosis** **Meiosis**

**Occur in** Somatic Cells Germ Cells

**No of Division** 1 2 = Meiosis I + II

**DNA Replication** S Phase = Once S Phase = Once

**Daughter Cells** 2 Diploid = 2n 4 Haploid = n

**Chromosome No** Same = Equational Half = Reductional

**Synapsis** No Yes = Zygotene

**Crossing Over** No Yes = Pachytene

**Function** Growth + Repair Gamete + Variation

**Duration** Short = Hours Long = Days to Years

### *5. SIGNIFICANCE + AMITOSIS*

*A. Significance of Mitosis*

1. Genetic Stability = Identical Cells

2. Growth of Multicellular Organism

3. Continuous Replacement = Skin, RBC Life = 120 Days

4. Asexual Reproduction + Regeneration = Planaria

*B. Significance of Meiosis*

1. Maintain Chromosome No Generation to Generation

2. Genetic Variation = Evolution Ka Base = Natural Selection

3. Crossing Over = New Gene Combinations

4. Independent Assortment = 2^n Combinations = Human = 2^23 = 8 Million Gametes

*C. Amitosis = Direct Division* `NEET Rare`

No Prophase, No Spindle = Nucleus Direct Constrict = 2 Parts

Example: Bacteria, Yeast, Foetal Membrane, Paramecium Macronucleus

### *6. LAST 5 YEAR PYQ ONE LINERS* `Ratta Maar Le`  

1. *Synaptonemal Complex* = Zygotene = Holds Homologous = NEET 2024  

2. *Metaphase* = Best Stage to Study Chromosome Morphology = NEET 2024  

3. *Crossing Over* = Pachytene = Non-Sister Chromatids = NEET 2023  

4. *G0 Phase* = Quiescent = Metabolically Active = NEET 2023  

5. *Anaphase I* = Homologous Separate = Reduction = NEET 2022  

6. *Interkinesis* = No DNA Replication = NEET 2022  

7. *Terminalisation* = Diakinesis = Chiasmata Ends Move = NEET 2021  

8. *Cell Plate* = Plant Cytokinesis = Phragmoplast = NEET 2021  

9. *Synapsis* = Zygotene = Bivalent Formation = NEET 2020  

10. *Colchicine* = Metaphase Arrest = Spindle Inhibitor = Polyploidy = NEET 2020  

11. *S Phase* = DNA Doubles, Chromosome No Same = NEET 2019  

12. *Syncytium* = No Cytokinesis = Liquid Endosperm = NEET 2019  

13. *Chiasmata* = Visible in Diplotene = X Shape = NEET 2018  

14. *Centromere Split* = Anaphase = Mitosis + Anaphase II = NEET 2017  

15. *Diplotene Arrest* = Oocytes = Dictyotene = NEET 2016  

### *7. GOOGLE SE HATKE TRICKS* 🔥  

*A. Meiosis I Prophase Sequence Yaad*

Lepto = Thin, Zygo = Jodi, Pache = Package Exchange, Diplo = X Dikhaya, Dia = Disappear

School Trick: **L**adki **Z**iddi **P**akka **D**eewani **D**ikhayi

*B. Anaphase Shape Yaad*

Metacentric = V Shape = Middle Centromere

Sub-Metacentric = L Shape = Slight Off Centre

Acrocentric = J Shape = Near End

Telocentric = I Shape = Terminal = No p arm

Trick: V L J I = **V**ery **L**arge **J**alebi **I**tem

*C. Mitosis vs Meiosis II Confusion*

Meiosis II = Mitosis of Haploid Cell = Sab Same Bas Shuru n se hota

Anaphase I = Chromosome Jata, Anaphase II = Chromatids Jate

*D. Chromosome vs Chromatid Count*

Human Cell G1 = 46 Chromosomes = 46 Chromatids = 2C DNA

After S Phase = 46 Chromosomes = 92 Chromatids = 4C DNA

After Anaphase = 92 Chromosomes = 92 Chromatids = Still 4C DNA

After Telophase = 46 Chromosomes = 46 Chromatids = 2C DNA Each Cell

*2-3Q Pakka Distribution*:  

1Q = Cell Cycle Phases + G0, 1Q = Prophase I Sequence, 1Q = Mitosis vs Meiosis ya Anaphase I vs II