Cell Cycle Cell Division • Why cell division?

• All cell reproduce by dividing into two with each parental cell give

rise to two daughter cell when divide

• Growth

• Repair Asexual Reproduction- Mitosis

• Reproduction→

Sexual Reproduction- Meiosois

• Term Mitosis by Flamming

• Term Meiosis by Former & Moore

Cell Cycle= Life of a Cell

Cell Division

G0= Cell Mature

Cell cycle- G1 → S → G2 → M Mitosis- Karyokinesis & Cytokinesis

Meiosis →Meiosis-I→Cytokinesis →

Interphase G1→S→G2 (Interkinesis) →Meiosis-II→Cytokinesis

Gap-I (Gap before S phase or DNA Duplication

G2= Gap-2 (Gap after S-phase or DNA Duplication)

Mitosis-Amount of DNA & Chromosome number

are same as G1 after mitotic division or in

product of mitotic division

G1 → S → G2

2n=4 2n=4 2n=4 Prophase Metaphase Anaphase Telophase Cytokinesis DNA=2C DNA=4C DNA=4C

2n=4 2n=4 2n=8

DNA=4C DNA=4C DNA=4C

2n=4 2n=4

DNA=2C DNA=2C

Meiosis- Reductional Division (Each Nucleus)

G1 → S → G2 → Meiosis-I → G1 → S → G2 → Meiosis-II → Cytokinesis

2n=4 2n=4 2n-4 *n=2 n=2 n=2 n=2 n=2 n=2 DNA=2C DNA=4C DNA=4C *DNA=2C DNA=2C DNA=2C DNA=2C DNA=C DNA=C

Meiosis-I

Prophase-I Metaphase-I Anaphase-I Telophase-I 2n=4 2n=4 2n-4 n=2 DNA=4C DNA=4C DNA=4C DNA=2C

Leptotene Zygotene Pachytene Diplotene Diakinesis Bouquet Stage - Synapsis -Crossing over -Chiasmata -Terminalization

-Bivalent/Tetrad -Recombination

-Synaptonemal Complex

Meiosis-II

Prophase-2 Metaphase-2 Anaphase-2 Telophase-2

N=2 n=2 n=4 n=2

DNA=2C DNA=2C DNA=2C DNA=C

Interphase- Cell is most active & duplicates the existing protoplasm

G1- Gap-I between M phase & S phase

G2- Gap-2 between S phase & M phase

S- Synthesis Phase- DNA replication phase

Go- Cell maturation/ Quiescent stage

• The sequence of events by which a cell duplicates its genome, synthesize the other

constituents of the cell and eventually divides into two daughter cells is cell cycle

• It is the life of a cell when cell is dividing there

is continuous synthesis of protoplasm in

quantity

DNA duplicates/replicates only in one stage S-Phase

• G1 Phase/ Pre- DNA Synthesis/ Gap-1 Phase

• Longest in plants 12-15 hours

• In human 5-6 hours

• Duplication of existing protoplasm i.e, cell

organelle duplication

• Synthesis of structural and functional protein

(structural like cell organelle, functional

protein means enzyme)

• Synthesis of RNA- mRNA, rRNA, tRNA

• Synthesis of enzymes

• Cell is metabolically active and grow in size cell grow maximum in G1 Phase

S Phase/Synthesis/DNA Synthesis Phase

• Replication of DNA (Nuclear DNA)

• Duplication of centrosome

• Synthesis of Histone protein

• Replication of cytoplasmic DNA (Mitosis-Plastid DNA) occurs in any phase of cell cycle

• DNA becomes double of G1 phase. If in G1 amount of DNA is 2C, than in S-phase it is 4C,

but no increase in chromosome number as i.e, if 2n=4 in G1 than same 2n=4 in S phase as

duplicated chromatin DNA are attached together

G2/Gap-2/Post DNA Synthesis/Pre-Mitotic Phase

• Longest in human

• Material required for M-phase/chromosomal division synthesized in this phase

• Synthesis of Tubulin protein which from spindle fibers

• Cell grows continuously

M-Phase/Division Phase

• Shortest, only 1 hour in human

• Actual division of chromosome and nucleus occurs

• In animal cell mitotic division occurs only in diploid somatic

cell except in some social insects ( honey bee- Drones (n)

show mitosis)

• In plants mitotic division occurs in both Haploid (Algae,

Bryophytes, Microspore, Megaspore cells) and Diploid cell

(Pteridophytes, Gymnosperms, Angiosperms, Somatic cells)

• Most dramatic phase of cell as involves major re-

organization of all components of cell

• Mitosis is an equational division, as number of chromosomes

are same in daughter cell

• It involves mainly nuclear division, with chromosome division

and cytokinesis

• Mitosis have 4 sub-phases

Prophase-

• First phase of karyokinesis

• Initiation of condensation of chromatin material, chromatin

untangled and start to condensed

• Centrosome (Duplicated in S-Phase) starts to move to

opposite poles

• Astral ray formation starts around the centrosome due to

gelation of protein around the centrosome ( Gelation- Gel

formation) in animal cell. Astral or Amphiastral Mitosis, in

plant cell the two poles are decided by microtubule

arrangement. No Aster ray formation in plants cell so called

anastral mitosis

• Centrosome radiate out the microtubules from spindle fiber

Prophase

Metaphase

Anaphase

Telophase

• Disappearance of nuclear membrane, nucleolus, Golgi

body, ER

Metaphase

• Complete disappearance of nuclear membrane

• Maximum condensation of chromatin so chromosomes

are clearly visible

• Each chromosome with two chromatids (replicated

chromatin) and centromere

• Chromosome with NOR also seen

• Structure/Morphology of chromosomes studied in metaphase stage

• Centromere have kinetochore (the protein disc) where spindle fibers are attached

• Chromosome are arranged in metaphase plate at equator

• One chromatid of each chromosome connected by kinetochore to spindle fibers from

opposite poles

• Centromere lies in center are arms laying towards opposite poles

• Two types of spindle fibers

o Chromosomal/Discontinuous/Kinetochore fibers form pole to centromere attached

to kinetochore

o Supporting/continuous/Non-Kinetochore Fibers run from pole to pole

• Key events

o Formation of metaphase plate

o Spindles attached to kinetochore disc

Anaphase

• Shortest in mitosis

• Division of centromere. Centromere of each

chromosome splits, sister chromatids separate, Kinetochore disc brakes

• Number of chromosomes become double in cell

• Each chromosome moves away from the equatorial plate. Centromere towards pole and

arms are towards equator

• The kinetochore microtubules shorten due to polymerization of Tubulin protein towards

kinetochore end. The centromere are pulled towards opposite poles

• Key events

o Division of centromere and chromatids separates

o Chromatids (now chromosome) moves towards opposite poles

Telophase

• Reverse of prophase

• Final stage of karyokinesis

• Chromosomes starts to decondense

• Nuclear membrane re-appears around chromosome clusters

at two opposite poles forming two daughter nuclei

• Nucleolus, Golgi complex, ER reforms

Cytokinesis

• Division of cytoplasm

• In animal cell –Furrow Formation by Constriction

• Microtubules & Microfilaments arrange on equator to form

middle body

• At the periphery of equator, a contractile ring is formed made

of actin and myosin protein

• Due to interaction between actin and myosin the ring contract

thus a furrow forms from outside towards inside in cell

• Furrow deepens continuously and ultimately a cell divides in to

two daughter cells

• Cytokinesis in animal cells is centripetal order (periphery to

center)

• In plant cell- By Cell Plate formation/Phragmoplast

• No furrow formation as cell wall is rigid

• Many Golgi vesicle are spindle microtubules arranged on equator to form cell plate or

phragmoplast. Also have fragments of E.R

• The membranes of Golgi vesicle fuse to form a plate like structure i.e, cell plate

• Golgi vesicle secretes (Ca-Mg Pactate) form middle lamella (by cell plate)

• Then deposition of cellulose and Hemicellulose on both side from the primary cell wall

• In plant cell plate formation occurs from center to periphery

• In some organisms, Karyokinesis is not followed by Cytokinesis, leads to multinucleate

condition- Syncytium Ex.-Liquid endosperm in Coconut

Significance of Mitosis

• Growth and development- Zygote to complete organism

• Cell repair Ex.- cells of upper layer of epidermis

• Cell lining of gut, blood cells are constantly replaced

• In plants, meristem cell (Apical, Lateral) continuously divides by mitosis throughout their

life

• To maintain karyokinesis index- KI- Vn/Vc-Vn

• Karyoplasmic Index/Nucleocytoplasmic Ratio

• KI= Vn/Vc-Vn KI α Vol. of Nucleus (Vn)

o KI α 1/Vc-Vn or KI α 1/ Volume of cytoplasm

• Small cell have less cytoplasm so more karyoplasmic Index (High KI)

• If cell is large, more cytoplasm or Low KI, so nucleus is not able to regulate/fulfill the

requirement of cytoplasm & cell activity so cell divides

Meiosis • Termed by Farmer & Moore

• Specialized cell division which reduces the number of chromosomes to half of its parent

cell so Reductional Division

• Meiosis is necessity of sexual reproduction and alternation of generation

Small Cell High KI No Division

Large Cell Low KI Cell Division

• Meiosis- Sexual reproduction= Alternation of generations are complementary to each

other

• Three types of meiosis in Living World

• Meiosis maintains the constancy of chromosome number from one generation to another

in sexually reproducing organism

• Meiosis involves two successive divisions

o Meiosis-I Karyokinesis→ Cytokinesis → Interkinesis

o Meiosis-II Karyokinesis → Cytokinesis

Four daughter cells are produced as the result of meiosis

• There may be or may not be cytokinesis and interkinesis (specially in Angiosperms). In

zygotic and gametic meiosis even in sporic meiosis also (up to Gymnosperms) there is

meiosis-I → Cytokinesis→ Interkinesis→Meiosis-II→Cytokinesis

• In interkinesis no S-phase i.e, no duplication of DNA as in meiosis-I, only homologous

pairs of chromosomes are separated (Reductional division) no division of chromosome

• Chromosome division occurs in meiosis-II , so the meiosis-II is same as mitosis

• If G-1 of meiosis-I have 2n=4, DNA=2C then, after meiosis 2nd n=2 and DNA=C in each

daughter cell.

• Meiosis-I is reductional division involves the pairing of homologous pair of chromosomes

crossing over leads to recombination between non sister chromatids of homologous pair

of chromosomes after its chromosome number become half

• Meiosis-II is Homotypic/Equational division similar to mitosis. As meiosis-I involves only

segregation of homologous pairs of chromosomes in two daughter cells but no division of

chromosomes. So division of chromosomes occurs in Meiosis 2nd

• Division of chromosomes occurs in Anaphase-II of Meiosis-II

• Anaphase-I involves only segregation of homologous pairs of chromosomes

Gametic

• only in animals (All) at time of gamete formation

Zygotic• only in Algae- in zygote

Sporic

• Bryophytes, Pteridophytes, Gymnosperm, Angiosperms. During formation of spore in

spore mother cell

• Anaphase-II involves division of chromosomes/centromere

o Meiosis-I, Interphase (G1→S→G2 are same as mitosis)

o Prophase-I, longer and most complex phase of meiosis. It has 5 sub-stages

• Leptotene

• Zygotene

• Pachytene

• Diplotene

• Diakinesis

Meiosis-I

Prophase-I

Leptotene-

o Chromatin threads starts condensation, forms chromosome

o Chromosomes are longest and thinnest and visible under light microscope

o All chromosome in nucleus are directed towards centrioles so group of

chromosome appear like Bouquet so Bouquet stage

Zygotene

o Synapsis- pairing of homologous pairs of chromosomes

o Bivalent/Tetrad- pair of homologous chromosome is now called as Bivalent or

Tetrad as two chromosomes have 4 chromatids

o Bivalents are more clearly visible in next stage that is pachytene

o Synaptonemal complex is formed by bivalents

o Synaptonemal complex involves bivalents made up of 3 lines 2DNA and middle

protein array like ladder

o Synthesis Of small amount of DNA (0.3%) occurs in zygotene stage called Z-DNA

which also helps in formation of synaptonemal complex

o Centrosome starts to move towards opposite pole

Pachytene-crossing over and recombination

o 4 chromatids of bivalent clearly appear as Tetrad, as longitudinal splitting of two

chromatids of a chromosome is now Dyad, and Bivalent becomes tetrad

o Attraction between homologous pairs of chromosomes increase

o Non sister chromatids of homologous pairs of chromosomes coiled around each

other to form recombination nodule and they exchange their part by breaking and

joining called as crossing over

o Formation of recombination nodule-Recombinase

o Exchange of parts by breaking- Endonuclease

o Joining/Reunion of exchange of exchange parts-Ligase and Recombinase enzymes

o Crossing over was discovered by Morgan in Drosophila

o Crossing over leads to exchange of genetic material between homologous pairs of

chromosomes

Diplotene- Desynepsis & Chiasmata

o Dissolution of synaptonemal complex (Desynepsis)

o Chiasmata-appears-‘X’ shaped structure

o Now homologous pairs of chromosomes repel each other leads to the cross (x) like

structure appearance i.e, chiasmata or crossing over

o Diplotene (Dictyotene) stage may suspends for years or months in oocytes of some

vertebrates (Human)

Diakinesis-terminalization

o The bivalents repel each other and migrate to the periphery of nucleus, leads to the

terminalization of chiasmata

o Chromosomes are fully condensed and meiotic spindles is assembled to prepare the

homologous pairs of chromosomes for separation

o Nuclear membrane and nucleolus start to disappear → centrosomes move to

opposite poles

o Transition phase to Metaphase-I

Metaphase-I

o Spindle formation

o Metaphase plate formation

o Chromosomal/Kinetochore/Discontinuous fibres attached with kinetochore of every

chromosome

o The two discs of kinetochore dissolves only one kinetochore is present in a

chromosome

o Formation of metaphase plate. The centromere aligns towards the pole and

chromatids towards the equator

Anaphase-I

o Segregation/Disjunction of homologous pair of chromosomes

o No division of centromere

o Kinetochore fibre pulls the chromosomes with two chromatids

o It is responsible for reduction in chromosome number in two nuclei and daughter

cells

Telophase-I

o Haploid number of chromosomes reach to opposite poles starts to decondense and

uncoil

o Nuclear membrane & nucleolus reappears

Cytokinesis

o In Animal cell= furrow formation

o In plant cell- by cell plate formation

o In angiosperms its very diverse as there may sequential meiosis (karyokinesis

followed by cytokinesis) or simultaneously meiosis (karyokinesis not followed by

cytokinesis or half sequential half simultaneous

o If simultaneous 4 nuclei are producing which are attached to gather form

microspore tetrad like in most angiosperms

Meiosis-II

• G1→S→G2 (Interkinesis) occurs before Meiosis-II

As usual but in S-phase no DNA replication as DNA is already replicated but chromosome are

still not divided as each chromosome of daughter cell of meiosis-I have 2 chromatids

Remaining all stages are like mitosis

o Prophase-II- formation of spindles fibres continuous & discontinuous

o Metaphase11Metaphase plate formation- like mitosis centromere at equator and

chromatids towards poles

o Anaphase-II- division of centromere

o Chromatids, now chromosome moves towards opposite poles

o Telophase-II- decondensation of chromosomes

o Appearance of nuclear membrane and nucleolus

o Spindle fibres disappears

o All 4 daughter cells are different from each other

o 50% parental and 50% new combination in all 4 daughter cells

Control of cell cycle

• Cell division is due cell signals which are regulated by cyclin protein and CDK enzyme

(Cyclin Dependent Kinase)

• Controlled by (cyclin protein as its

concentration is changed in cyclic manner in

cell) & (CdK’s= Cyclin dependent kinase,

catalyze the breakdown of ATP & do the

phosphorylation of cyclin protein and

deactivate it

• Two check points

o G1→S check point

o G2→M check point

• Both cyclin protein &Cdk’s are called as MPF

= maturation promoting factor

• At G1-S check point the S-CdK binds with cyclin activates it and cell enters into S-phase

• Then S-kinase separates & S-cyclin breaks in to fragments (low concentration) ie, S-kinase

becomes inactive

• G2→ M check point

• The M-kinase binds with M-cyclin and activates it & cell enters in M-phase

• Then M-kinase separates & inactive & M-cyclin break down into fragments

Modifications of Mitosis

• Amitosis- In prokaryotes and some unicellular eukaryotes

• No chromatin (in prokaryotes), no appearance of chromosome and spindles

• Nuclear envelope also not degenerate

• The nucleus elongates, constrict from middle to form two daughter nuclei, it is followed by

centripetal constriction of cytoplasm to form two daughter cells

• Direct cell division

• Division of chloroplast in to Eukaryotes,Amoeba, Paramecium

• Ex- PPLO, BGA, Bacteria (Prokaryotes)

• Free Nuclear Division-Karyokinesis not followed by cytokinesis leads to

multi-nucleate condition

Pre-Mitosis/Promitosis/Cryptomitosis/Intranuclear Mitosis

• Ex- some Protozoa, Animals- No nuclear membrane disappearance

• Centrosome present inside nucleus, spindle formation within nuclear membrane

Dinomitosis

• In Dinoflagellates/Mesokaryotes, DNA without histone so not condense properly, but

nuclear membrane does not disappear

• Not condense properly but nuclear membrane does not disappear

• Spindle formation within nuclear membrane

Endomitosis

• Duplication of chromosomes without nuclear division

• Leads to polyploidy

• Colchicine mitotic poison, induce polyploidy in plants as arrests the spindle formation

• Increase in number of chromosome in set

Endoreduplication

• Modified endomitosis, repetitive duplication of chromatin but no division of centromere

so many chromatids are attached with one cetromere = Polytene Chromosomes

Check Your Concept 1. First gap phase in cell cycle is :-

A. Interval between mitotic phase and DNA replication phase

B. Interval between DNA replication phase and DNA separation phase

C. Interval between karyokinesis and cytokinesis

D. Interval between DNA replication phase and second gap phase

2. The two chromatids of a metaphase chromosome represent: -

A. Replicated DNA to be separated at anaphase

B. Non homologous chromosomes joined at the centromere

C. Pair of homologous chromosomes

D. Maternal and paternal chromosomes joined at the centromere

3. A cell that is entering the mitotic phase (M-phase) of cell cycle is :-

A. Always haploid and with duplicated chromosomes

B. Either haploid or diploid and with duplicated chromosomes

C. Either haploid or diploid and with duplicated or unduplicated chromosomes

D. Always diploid and with unduplicated chromosomes

4. A cell examined during prophase of cell cycle contained 100 units of DNA and 50

chromosomes. What would be the number of DNA and chromosomes in anaphase of this cell

cycle?

A. 200 DNA & 100 chromosomes

B. 100 DNA & 50 chromosomes

C. 100 DNA & 100 chromosomes

D. 50 DNA & 25 chromosomes

5. Which type of chromosome is present in the prophase of cell cycle?

A. 2 chromatids

B. 1 chromatid

C. 4 chromatids

D. 8 chromatids

6. Synaptonemal complex is a nucleoprotein structure. It is visible or found from-

A. Zygotene to pachytene

B. Leptotene to diplotene

C. Zygotene to metaphase

D. Pachytene to diplotene

7. Which one of the following is correctly matched?

A. Leptotene - formation of bivalents

B. Diplotene - chiasmata appear

C. Pachytene - chiasmata terminalization

D. Zygotene - formation of bouquet

8. In which stage of meiosis, chromosomes are thin, long, thread like?

A. Zygotene

B. Leptotene

C. Pachytene

D. Diakinesis

9 Meiosis involves-

A. One nuclear division and one chromosome division

B. Two nuclear divisions and one chromosome division

C. One nuclear division and two chromosome divisions

D. Two nuclear divisions and two chromosome divisions

10. In meiosis, centromeres of chromosomes divide during-

A. Anaphase of meiosis-II

B. Metaphase of meiosis-I

C. Anaphase of meiosis-I

D. Prophase of meiosis-II

11. Which of the following not occurs in Anaphase–I but occurs in Anaphase–II :–

A. Condensation of chromosomes

B. Poleward movement of chromosome

C. Contraction of spindle fibers

D. Splitting of centromere

12. Crossing over takes place in :-

A. Zygotene

B. Pachytene

C. Diplotene

D. Diakinesis

13. A contractile mid body forms during cytokinesis in :-

A. Animals

B. Higher plants

C. Fungi

D. Algae

14. Which of the two events restore the normal number of chromosomes in life cycle of sexually

reproducing organisms?

A. Mitosis and Meiosis

B. Meiosis and fertilization

C. Fertilization and mitosis

D. Only meiosis

15. Match the column–I with column–II and select the correct answer :-

Column–I Column–II

(A) Pachytene (i) Bouquet stage

(B) Zygotene (ii) Chiasma visible

(C) Diplotene (iii) Terminalization

(D) Leptotene (iv) Gene exchange

(E) Diakinesis (v) Synapsis

A. A–i, B–ii, C–iii, D–iv, E–v

B. A–iv, B–v, C–ii, D–i, E–iii

C. A–iii, B–iv, C–v, D–ii, E–i

D. A–ii, B–iii, C–iv, D–i, E–v

16. Nuclear envelope reappears at :-

A. Metaphase

B. Prophase

C. Anaphase

D. Telophase

17. Slipping of chiasmata towards the ends of bivalent is called :-

A. Terminalization

B. Diakinesis

C. Interkinesis

D. Congregation

18. In meiosis, how many cycles of chromosome division occurs ?

A. One

B. Four

C. Two

D. Three

19. Which does not occurs in prophase?

A. Decondensation of chromatin

B. Condensation of chromatin

C. Appearance of chromosome

D. Disappearance of nuclear membrane and nucleolus

20. In which stage of cell division, number of chromosomes best counted: -

A. Prophase

B. Metaphase

C. Telophase

D. Interphase

21. How many chromosomes shall be present in a diploid cell at mitotic anaphase if its egg cell

has ten chromosomes: -

A. 10 (Ten)

B. 20 (Twenty)

C. 30 (Thirty)

D. 40 (Forty)

22. At anaphase - II of meiosis each chromosome contains: -

A. 4 DNA

B. 3 - DNA

C. 2 - DNA

D. 1 – DNA

23. In Anaphase – I each chromosome composed of:-

A. One chromatid

B. Two chromatid

C. Four chromatid

D. Many chromatid

24. In meiosis, division of centromere occurs during:-

A. Interphase

B. Anaphase - I

C. Anaphase - II

D. Metaphase - I

25. In meiosis, nuclear membrane and nucleolus disappear during :-

A. Zygotene

B. Pachytene

C. Diakinesis

D. Metaphase – I

26. Separation of homologous chromosomes during Anaphase - I is called :-

A. Synapsis

B. Disjunction

C. Nondisjunction

D. Crossing over

27. During cell division, spindle fibers attach to which part of chromosome :-

A. Primary constriction

B. Secondary constriction

C. Telomere

D. Satellite

28. Synaptonemal complex is characteristic of :–

A. Mitotic chromosomes

B. Leptotene chromosomes

C. Paired meiotic chromosomes

D. Metaphase

29. Each chromosome composed of one chromatid in:-

A. Anaphase – I

B. Anaphase – II

C. Metaphase – I

D. Metaphase – II

30. If the number of bivalents are 8 in metaphase – I, what shall be the number of chromosomes

in daughter cells after meiosis – I and meiosis – II respectively:-

A. 8 and 4

B. 4 and 4

C. 8 and 8

D. 16 and 8

31. Which one of the following statements is correct?

A. Cell divided by cytokinesis only in mitosis

B. DNA is replicated before the start of meiosis only

C. Spindles consisting of microtubules are formed only in mitosis

D. Exchange of genetic materials occurs only in meiosis

32. In meiosis :-

A. Division of nucleus twice but replication of DNA only once

B. Division of nucleus twice and replication of DNA twice

C. Division of nucleus once and replication of DNA is also once

D. Division of nucleus once and DNA - replication is twice

33. After meiosis - I, the two chromatids of a chromosome are :-

A. Genetically similar

B. Genetically different

C. There occurs only one chromatid in each chromosome

D. None of the above

34. Chiasmata appears during :-

A. Diakinesis

B. Pachytene

C. Diplotene

D. Leptotene

35. During telophase :-

A. Nuclear membrane is formed

B. Nucleolus appears

C. Astral rays disappear

D. All the above

36. Pairing of homologous chromosomes is called:-

A. Disjunction

B. Synapsis

C. Segregation

D. Polyteny

37. Synaptonemal complex first appear :–

A. Leptotene

B. Pachytene

C. Zygotene

D. Diplotene

38. The correct sequence of prophase–I of meiosis is :–

A. Leptotene, pachytene, zygotene, diplotene, diakinesis

B. Leptotene, diplotene, pachytene, zygotene, diakinesis

C. Leptotene, zygotene, pachytene, diplotene, diakinesis

D. Leptotene, zygotene, diakinesis, diplotene

39. The significance of Meiosis is that it –

A. Produce four cells having chromosomal number equal to mother cell

B. Occurs in all types of cells

C. Maintains the constant Chromosomes number to a particular species

D. Growth of animal body organs

40. Crossing over that results in genetic recombination in higher organisms occurs between –

A. Non-sister chromatids of a bivalent

B. Two daughter nuclei

C. Two different bivalents

D. Sister chromatids of a bivalents

41. At which stage of the cell cycle are histone proteins synthesized in a eukaryotic cell ?

A. During telophase

B. During S–phase

C. During G2–stage of prophase

D. During entire prophase

42. If the n=16 in plant cell then what is possible in metaphase - I of meiosis ?

A. 32 Bivalents

B. 16 Tetravalent

C. 16 Bivalents

D. 32 Bivalents

43. Meiosis involves:

A. Pairing of homologous chromosomes and recombination between sister chromatids of

nonhomologous chromosomes

B. Pairing of homologous chromosomes and recombination between non sister chromatids

of homologous chromosomes

C. Pairing of nonhomologous chromosomes and recombination between non sister

chromatids of homologous chromosomes

D. Pairing of homologous chromosomes and recombination between sister chromatids of

homologous chromosomes

44. In which one of the following stage, the four chromatids of each bivalent chromosomes

becomes distinct and clearly appears as tetrads.

A. Leptotene

B. Zygotene

C. Pachytene

D. Diplotene

45. The product of mitosis are –

A. One nucleus containing twice as much DNA as the parent nucleus

B. Two genetically different cells

C. Four nuclei containing half as much DNA as the parent nucleus

D. Two genetically identical nuclei

46. Mature nerve cells are incapable of cell division. These cells are probably in –

A. G0 phase

B. The S phase

C. G2 phase

D. G1 phase

47. The microtubules of the mitotic spindle attach to a specialized structure in the centromere

region of each chromosome, called the –

A. Kinetochore

B. Nucleosome

C. Equatorial plate

D. Centrosome

48. In plant cells, cytokinesis is accomplished by the formation of

A. Membrane furrow

B. Equatorial plate

C. Cell plate

D. Spindle

49. Meiosis can occur –

A. In all sexually reproducing organisms

B. Only when an organism is diploid

C. Only in multicellular organisms

D. Only in haploid organisms

50. During meiosis, the sister chromatids separate during –

A. Anaphase II

B. Anaphase I

C. The S phase

D. Synapsis

51. At the end of the first meiotic division, each chromosome consists of –

A. A homologous chromosome pair

B. Four copies of each DNA molecule

C. Two chromatids

D. A pair of polar microtubules

52. Genetic recombination between chromosomes occurs during –

A. Prophase of meiosis I

B. Interphase preceding meiosis II

C. Mitotic telophase

D. Fertilization

53. The number of chromosomes is reduced to half during –

A. Anaphase of mitosis and meiosis

B. Meiosis II

C. Meiosis I

D. Fertilization

54. Chromosome number is reduced during meiosis because the process consists of –

A. Two cell divisions without any chromosome replication

B. A single cell division without any chromosome replication

C. Two cell division in which half of the chromosomes are destroyed

D. Two cell divisions and only single round of chromosome replication

55. Which of the following does not occur during mitotic prophase?

A. Disappearance of the nuclear envelope

B. Chromosome condensation

C. Migration of centrioles towards the cell poles

D. Synapsis of homologous chromosomes

56. Meiosis takes place in

A. Conidia

B. Gemmule

C. Megaspore

D. Meiocyte

57. Which is otherwise called quiescent stage?

A. G0

B. G2

C. G1

D. S-phase

58. Cells in G0-stage –

A. Are metabolically more active

B. Are metabolically inactive

C. Remain metabolically active but no longer proliferate in normal condition

D. None

59. Diplotene can lasts for months or years in –

A. Oocytes of all vertebrates

B. Oocytes of all invertebrates

C. Oocytes of some vertebrates

D. Spermatocytes of all vertebrates

60. Which one is false about G1-phase (Gap-I)?

A. It occurs between M and S phase

B. In it cells are metabolically active and continuously grow

C. It is pre-synthetic or post mitotic phase

D. In this phase DNA replicates

61. Which one is false statement about G2-phase?

A. It is post-S and Pre M-phase

B. In this phase cell has quantity of DNA in each cell is 4C if the DNA in G1 phase is 2C

C. In it G0 resides

D. Proteins like tubulin is formed for mitosis as well as cell growth continues

62. If mitotic division is arrested in G1 phase of a cell cycle, then the condition is known as –

A. G2 phase

B. S phase

C. G0 phase

D. M-phase

63. Which of the following statements is false?

A. Mitosis or the equational division occurs in both N and 2N cells

B. In onion 2N = 16

C. Growth and reproduction are characteristics of cells indeed of all living organism

D. In plants meristematic tissues show meiosis

64. Which of the following is not a function of mitotic cell division in animals ?

A. Growth and repair

B. Cell replacement

C. Asexual reproduction

D. Gametes formation

65. Phragmoplasts formed by vesicles of GB are the precursors of –

A. Cell plate

B. Chloroplasts

C. Chromoplast

D. Protoplast

66. Label the structure indicated by lines (i), (ii), (iii) and (iv) –

A. (i) – Chromatid, (ii) Centriole, (iii) Centromere, (iv) Chromosome

B. (i) – Chromosome, (ii) Centriole, (iii) Centromere, (iv) Chromatid

C. (i) – Chromatid, (ii) Centromere, (iii) Centriole, (iv) Chromosome

D. (i) – Chromosome (ii) Centromere, (iii) Centriole, (iv) Chromatid

67. Asexual reproduction produces genetically identical individuals because –

A. Chromosome do not have to replicate

B. It involves chromosomes replication without cytokinesis

C. No meiosis or fertilization takes place

D. The only cell division that occurs in meiosis

68. Which one is correct about meiosis ?

A. First division is reduction and second division is equational

B. The best material for the study of meiosis is microspore (pollen) mother cell in

microsporangium of anther

C. The importance of meiosis lies in maintaining the chromosomal number from generation to

generation in sexually reproducing organisms

D. All

69. A bivalent consists of

A. Two chromatids and one centromere

B. Four chromatids and two centromeres

C. Two chromatids and two centromeres

D. Four chromatids and four centromeres

70. At which stage of meiosis does the genetic constitution of gametes is finally decided

A. Metaphase I

B. Anaphase II

C. Metaphase II

D. Anaphase I

71. During anaphase-I of meiosis

A. Homologous chromosomes separate

B. Non-homologous autosomes separate

C. Sister chromatids separate

D. Non-sister chromatids separate

72. A bivalent of meiosis-I consists of

A. Two chromatids and one centromere

B. Two chromatids and two centromere

C. Four chromatids and two centromere

D. Four chromatids and four centromere

73. Identify the wrong statement about meiosis

A. Pairing of homologous chromosomes

B. Four haploid cells are formed

C. At the end of meiosis the number of chromosomes are reduced to half

D. Two cycle of DNA replication occurs

74. The centromere duplicates during the

A. G2 – phase of cell cycle

B. S – phase of cell cycle

C. Prophase of cell cycle

D. G1 – phase of cell cycle

75. Select the CORRECT statement related to mitosis

A. Amount of DNA in the parent cell is first halved and then distributed into two daughter cells

B. Amount of DNA in the parent cell is first doubled and then distributed into two daughter

cells

C. Amount of DNA in the parent cell is first halved and then distributed into four daughter cells

D. Amount of DNA in the parent cell is first doubled and then distributed into four daughter

cells

76. Select the correct option.

Column I Column II

A. Synapsis aligns homologous chromosomes (i) Anaphase-II

B. Synthesis of RNA and protein (ii) Zygotene

C. Action of enzyme recombinase (iii) G2-phase

D. Centromeres do not separate but chromatids (iv) Anaphase - I

move towards opposite poles (v) Pachytene

A. A – (i), B – (ii), C – (v), D – (iv)

B. A – (ii), B – (iii), C – (iv), D – (v)

C. A – (ii), B – (i), C – (iii), D – (iv)

D. A – (ii), B – (iii), C – (v), D – (iv)

78. A somatic cell that has just completed the S phase of its cell cycle, as compared to gamete

of the same species, has

A. Twice the number of chromosomes and four times the amount of DNA

B. Four times the number of chromosomes and twice the amount of DNA

C. Twice the number of chromosomes and twice the amount of DNA

D. Same number of chromosomes but twice the amount of DNA

79. How many chromosome shall be present in a diploid cell at mitotic anaphase if its egg cell

has 10 chromosomes?

A. 10

B. 40

C. 30

D. 20

80. Spindle fibres attach on to : –

A. Telomere of the chromosome

B. Kinetochore of the chromosome

C. Centromere of the chromosome

D. Kinetosome of the chromosome

81. In which stage of meiosis homologous chromosomes are segregated?

A. Metaphase I

B. Anaphase I

C. Anaphase 2

D. Metaphase II

82. Which of the following is not true for meiosis?

A. Production of genetic variability

B. Maintaining constancy of chromosome number during sexual reproduction

C. Reduction of chromosome number to one half

D. Production of diploid cell

83. At the completion of meiosis I, each human cell contains

A. 23 chromosomes, 46 chromatids

B. 46 chromosomes, 46 chromatids

C. 46 chromosomes, 92 chromatids

D. 23 chromosomes, 23 chromatids

84. Nerve and muscle cells are in this phase:

A. G0

B. G1

C. S

D. G2

85. In order to enter the cell cycle a cell must be stimulated from outside. What type of molecule

provides this stimulation?

A. Cyclins

B. Cyclin-dependent kinases

C. Cytokines and growth factors

D. Tyrosine kinases

86. Passage through which checkpoint is the step which commits the cell to proceed through to

mitosis and cell division?

A. G1 to S.

B. S to G2.

C. G2 to M.

D. M to G1.

87. Segregation of Mendelian factors (Aa) occurs during

A. Diplotene

B. Anaphase I

C. Zygotene/Pachytene

D. Anaphase II

88. Which is not characteristic of meiosis

A. Two stage of DNA replication, first before meiosis I and Second before meiosis II

B. Recombination and crossing over

C. Sister chromatids separate during anaphase II

D. Nuclear membrane disappears towards the end of Prophase

89. Consider a diploid organism with 2n= 4 and DNA=2C. How many chromosomes and DNA

molecules respectively are present in the G1 and G2 phases of somatic cell of this organism?

A. G1 : 4 and 4C ; : G24 and 4C

B. G1 : 4 and 2C ; : G24 and 4C

C. G1 : 4 and 4C ; : G28 and 4C

D. G1 : 4 and 4C ; : G28 and 8C

90. The correct sequence of phases of cell cycle is :

A. M → G1 → G2 → S

B. G1 → G2 → S → M

C. S → G1 → G2 → M

D. G1 → S → G2 → M

91. DNA sequence responsible for chromatid separation

A. Centromere

B. Telomere

C. NOR

D. Satellite

92. Crossing over takes place between which chromatids and in which stage of the cell cycle?

A. Non-sister chromatids on non-homologous chromosomes at Pachytene stage of prophase I

B. Non-sister chromatids of non-homologous chromosomes at Zygotene stage of prophase I

C. Non-sister chromatids of homologous chromosomes at Pachytene stage of prophase I

D. Non-sister chromatids of homologous chromosomes at Zygotene stage of prophase I

93. After meiosis I, the resultant daughter cells have

A. Four times the amount of DNA in comparison to haploid gamete.

B. Same amount of DNA as in the parent cell in S phase.

C. Twice the amount of DNA in comparison to haploid gamete.

D. Same amount of DNA in comparison to haploid gamete.

1. A 2. A 3. B 4. C 5. A 6. A 7. B

8. B 9. B 10. A 11. D 12. B 13. A 14. B

15. B 16. D 17. A 18. A 19. A 20. B 21. D

22. D 23. B 24. C 25. C 26. B 27. A 28. C

29. B 30. C 31. D 32. A 33. B 34. C 35. D

36. B 37. C 38. C 39. C 40. A 41. B 42. C

43. B 44. C 45. D 46. A 47. A 48. C 49. A

50. A 51. C 52. A 53. C 54. D 55. D 56. D

57. A 58. C 59. C 60. D 61. C 62. C 63. D

64. D 65. A 66. A 67. C 68. D 69. B 70. B

71. A 72. C 73. D 74. B 75. B 76. D 77. A

78. A 79. B 80. B 81. C 82. D 83. A 84. A

85. B 86. A 87. D 88. A 89. B 90. D 91. A

92. C 93. C

Previous Year Questions NEET-2020

1. Match the following with respect to meiosis

a. Zygote i. Terminalization

b. Pachytene ii. Chiasmata

c. Diplotene iii. Crossing over

d. Diakinesis iv. Synapsis

A. a-ii, b-iv, c-iii, d-i

B. a-iii, b-iv, c-i, d-ii

C. a-iv, b-iii, c-ii, d-I

D. a-i, b-ii, c-iv, d-iii

2. Identify the correct statement with regard to G1 phase of interphase?

A. Nuclear division takes place

B. DNA synthesis or replication takes place

C. Reorganization of all cell components takes place

D. Cell is metabolically active, grows but does not replicate its DNA

3. Some dividing cell exit the cell cycle and enter vegetative inactive stage. This is called

quiescent stage G0 the process occurs at the end of

A. G2 phase

B. M phase

C. G1 phase

D. S phase

4. The process of growth is maximum during

A. Dormancy

B. Log phase

C. Lag phase

D. Senescence

5. Dissolution of the synaptonemal complex occurs during

A. Leptotene

B. Pachytene

C. Zygotene

D. Diplotene

NEET-2019

6. The correct sequence of phases of cell cycle is

A. M, G1, G2, S

B. G1, G2, S, M

C. S, G1, G2, M

D. G1, S, G2, M

7. Cells in G0 phase

A. Exit the cell cycle

B. Enter the cell cycle

C. Suspend the cell cycle

D. Terminate the cell cycle

NEET-2018

8. The stage during which separation of the paired homologous chromosomes begin is

A. Temperature

B. Light

C. O2 concentration

D. Co2 concentration

NEET-2017

9. Which one of the following options gives the correct sequence of events during mitosis?

A. Condensation, nuclear membrane, disassembly, arrangement at equator,

centromere division, segregation, telophase

B. Condensation, crossing over, nuclear membrane disassembly, segregation,

telophase

C. Condensation, arrangement at equator, centromere division, segregation, telophase

D. Condensation, nuclear membrane disassembly, crossing over, segregation,

telophase

10. Anaphase promoting complex is a protein degradation machinery necessary for proper

mitosis of animal cells. If APC is defective in a human cell, which one of the following is

expected to occur?

A. Chromosome will be fragmented

B. Chromosomes will not segregate

C. Recombination of chromosome arms will occur

D. Chromosomes will not condense

NEET-II-2016

11. During cell growth, DNA synthesis takes place in

A. G2 phase

B. M phase

C. S phase

D. G1 phase

12. When cell has stalled DNA replication fork, which checkpoint should be predominantly

activated?

A. M

B. G2/M and M

C. G1/S

D. G2/M

13. Match the following

a. Pachytene i. pairing of homologous chromosomes

b. Metaphase-I ii. Terminalization of chiasmata

c. Diakinesis iii. Crossing over takes place

d. Zygotene iv. Chromosomes align at equatorial plate

A. a-ii, b-iv, c-iii, d-i

B. a-iv, b-iii, c-ii, d-i

C. a-iii, b-iv, c-ii, d-I

D. a-i, b-iv, c-ii, d-iii

NEET-I-2016

14. in meiosis crossing over is initiated at

A. pachytene

B. Leptotene

C. Zygotene

D. Diplotene

15. A cell at telophase stage is observed by a student in a plant brought from the field. He

tells his teacher that this cell is not like other cells at telophase stage. There is no

formation of cell plate and thus the cell is containing more number of chromosomes as

compared to other dividing cells. This would result in

A. Aneuploidy

B. Polyploidy

C. Somaclonal variation

D. Polyteny

AIIMS-2015

16. During cell cycle in which phase normal components of cell are synthesized and

assembled?

A. S

B. G2

C. G1

D. M

Re-AIPMT 2015

17. Arrange the following event of meiosis in correct sequence

a. Crossing over

b. Synapsis

c. Terminalization of chiasmata

d. Disappearance of nucleolus

A. b, c, d, a

B. b, a, d, c

C. b, a, c, d

D. a, b, c, d

AIPMT-2015

18. A somatic cell that has just completed the S phase of its cell cycle, as compared to gamete

of the same species, has

A. Same number of chromosomes but twice the amount of DNA

B. Twice the number of chromosomes and four times the amount of DNA

C. Four times the number of chromosomes and twice the amount of DNA

D. Twice the number of chromosomes and twice the amount of DNA

AIIMS-2014

19. Which of the following is the longest phase of the cell cycle?

A. Prophase

B. Interphase

C. Telophase

D. M phase

AIPMT-2014

20. During which phase of cell cycle, amount of DNA in a cell remains at 4C level if the initial

amount is denoted as 2C?

A. G0 and G1

B. G1 and S

C. Only G2

D. G2 and M

21. In S phase of the cell cycle

A. Amount of DNA doubles in each cell

B. Amount of DNA remains same in each cell

C. Chromosome number is increased

D. Amount of DNA is reduced to half in each cell

22. The enzyme recombinase is required at which stage of meiosis?

A. Pachytene

B. Zygotene

C. Diplotene

D. Diakinesis

NEET-UG-2013

23. A stage in cell division is shown in the figure. Select the answer which gives correct

identification of the stage with its characteristics

A. Telophase- Endoplasmic reticulum and nucleolus not reformed yet

B. Telophase- Nuclear envelope reforms, golgi complex reforms

C. Lata anaphase- chromosomes move away from equatorial plate,

golgi complex not present

D. Cytokinesis- Cell plate formed, mitochondria distributed between

two daughter cells

24. The complex formed by a pair of synapsed homologous chromosomes is called

A. Axoneme

B. Equatorial plate

C. Kinetochore

D. Bivalent

AIIMS-2012

25. Which of the following is wrong about G1 phase?

A. G1 stage followed by Mitosis

B. Cell is metabolically active

C. Cell grows continuously

D. Cell does not replicate its DNA

AIPMT Mains-2012

26. Identify the meiotic stage in which the homologous chromosomes separate while the

sister chromatids remain associated at their centromeres?

A. Anaphase-I

B. Anaphase-II

C. Metaphase-I

D. Metaphase-II

AIPMT Pre-2012

27. During gamete formation, the enzyme recombinase participates during

A. Prophase-I

B. Prophase-II

C. Metaphase-I

D. Anaphase-II

28. Given below is the representation of a certain event at a particular stage of a type of cell

division. Which is this stage?

A. Prophase of Mitosis

B. Both prophase and metaphase of mitosis

C. Prophase I during meiosis

D. Prophase II during meiosis

AIIMS-2011

29. Meiosis is not having the one of the characters out of the four given below

A. It involves two stages of DNA replication, one before meiosis-I and another before

meiosis II

B. It involves recombination and crossing over

C. Sister chromatids separate during anaphase II

D. Nuclear membrane disappears during prophase

AIPMT Mains-2011

30. At metaphase, chromosomes are attached to the spindle fibres by their

A. Centromere

B. Satellites

C. Secondary constriction

D. Kinetochore

AIPMT Pre-2011

31. Select the correct option with respect to mitosis

A. Chromatids separate but remain in the center of the cell in anaphase

B. Chromatids start moving towards opposite poles in telophase

C. Golgi complex and endoplasmic reticulum are still visible at the end of prophase

D. Chromosomes move to the spindle equator and get aligned along equatorial plate in

metaphase

AIPMT Pre 2010

32. During mitosis ER and nucleolus begin to disappear at

A. Early prophase

B. Late prophase

C. Early metaphase

D. Late metaphase

33. Which stages of cell division do the following figures A and B represent respectively?

A. Prophase – Anaphase

B. Metaphase- Telophase

C. Telophase – Metaphase

D. Late anaphase – Prophase

AIPMT-2009

34. Synapsis occurs between

A. Two homologous chromosomes

B. A male and a female gamete

C. mRNA and Ribosomes

D. spindle fibre and centromere

35. Given below is the schematic break-up of the phases/stages of the cell cycle?

Which one of the following is the correct indication of the stage/phase in the cell cycle?

A. A-Cytokinesis

B. B-Metaphase

C. C-Karyokinesis

D. D-Synthetic phase

1. C 2. D 3. C 4. B 5. D 6. D 7. A

8. C 9. A 10. B 11. C 12. D 13. C 14. A

15. B 16. C 17. C 18. B 19. B 20. D 21. A

22. A 23. B 24. D 25. A 26. A 27. B 28. C

29. A 30. D 31. D 32. B 33. D 34. A 35. D