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The correct answer is (C) pachytene

The correct answer is (C) non-sister chromatids of homologues

The correct answer is (A) chiasmata

1. As mitosis is equational division, the chromosome number is maintained constant.

2. It ensures equal distribution of the nuclear and the cytoplasmic content between the daughter cells, both quantitatively and qualitatively.

Therefore, the process of mitosis also maintains the nucleo-cytoplasmic ratio. 

3. The DNA is also equally distributed. 

4. It helps in growth and development of organisms. 

5. Old and worn-out cells are replaced through mitosis. getative propagation in plants.

6. It helps in the asexual reproduction of organisms and vegetative propagation in plants.

(B) Condensation → nuclear membrane disassembly → arrangement at equator → centromere division → segregation → telophase

Microtubules for if Tarbipolar spindle in Metaphase stage.

The part of the cell associated with heredity is Chromosome.

In our body meiosis occurs in germ cells i.e. in gonads.

Every cell capable of cell division pas ses through different stages or phases in a cyclic maimer. It is called the cell cycle.

1. G₀ is the phase of the cell cycle in eukaryotes in which many cell types stop dividing. It is also called a quiescent stage. 

2. If cells are deprived of appropriate growth factors, they stop at the Gi checkpoint of the cell cycle. Their growth and division are arrested and they remain in G₀ phase. 

3. Mature neurons and muscle cells remain in G₀ phase.

1. A karyotype is a representation of condensed chromosomes arranged in pairs. 

2. Analysis of the karyotype of a particular individual indicates whether the individual has a normal set of chromosomes or whether there are abnormalities in number or appearance of individual chromosomes.

1. Sequential events occurring in the life of a cell is called cell cycle. 

2. Interphase and M – phase are the two phases of cell cycle. 

3. Cell undergoes growth or rest during interphase and divides during M – phase.

1. The process of mitosis maintains the nucleo-cytoplasmic ratio. 

2. Apoptosis involves the cell death, but it benefits the organism as a whole. 

3. Crossing over takes place in pachytene phase of Prophase-I.

(a) Anaphase I, 

(b) Telophase I.

(a) Anaphase, (b) Metaphase, (c) Telophase.

1. Centriole, 

2. Spindle fibres, 

3. Chromosomes, 

4. Centromere. 

5. Daughter nuclei.

1. The chromosomes in root cell will be 16 as root cell is a diploid cell. 

2. The chromosomes in pollen grain will be 8 as pollen grain is a haploid cell. 

a. A wound is an injury to living tissue. 

b. Healing of wound take place by mitosis. 

c. Repetitive mitotic divisions near the site of injury results in healing of wound.

(i) It is a plant cell because it has cell wall.

(ii) 1. Chromatids 2. Spindle fibres 3. Centromere.

(iii) Anaphase.

1. The given figure is incorrect as the spindle fibres are not attached to centromere of the chromosomes. 

2. During metaphase, chromosomes are attached to spindle fibres with the help of centromeres.

1. Meiotic division produces gametes or spores. 

2. If it is absent, the number of chromosomes would double or quadruple resulting in the formation of monstrosities (abnormal gametes). 

3. The constant number of chromosomes in a given species across generations is maintained by meiosis and fertilization. 

4. Because of crossing over, exchange of genetic material takes place leading to genetic variations, which are the raw materials for evolution. 

5. Gametes are produced by the process of meiosis which are essential for sexual reproduction. 

6. Diploid organisms have two set of chromosomes (one paternal and one maternal). 

7. For a diploid organism to undergo sexual reproduction it needs to create gametes that contain only one set of chromosomes so the number of chromosomes remains same in the next generation. 

8. In absence of meiosis, the chromosome number of parents and their offsprings will differ in every generation; hence no species will hold its characters. 

9. Also, there will be no crossing over of homologous chromosomes. Thus, there will be no variations with respect to the changing environment in progeny to maintain their existence, which may lead to extinction of species.

Two haploid cells formed during first meiotic division divide further into four haploid cells this division is called homotypic division. It consists of five phases: prophase – II, metaphase – II, anaphase – II, telophase – II, and Cytokinesis – II. 

1. Prophase-II: 

a. The chromosomes are distinct with two chromatids. 

b. Each centriole divides into two resulting in formation of two centrioles which migrate to opposite poles and form asters. 

c. Spindle fibres are formed between the centrioles. 

d. The nuclear membrane and nucleolus disappears in this phase. 

2. Metaphase -II: 

a. Chromosomes are arranged at the equator. 

b. The two chromatids of each chromosome are separated by division of the centromere. 

c. Some of the spindle fibres are attached to the centromeres and some are arranged end to end between two opposite centrioles. 

3. Anaphase – II: 

In this phase, the separated chromatids become daughter chromosomes and move to opposite poles due to the contraction of the spindle fibres attached to centromeres. 

4. Telophase – II: 

a. In this stage daughter chromosomes starts to uncoil. 

b. The nuclear membrane surrounds each group of chromosomes. 

c. Nucleolus reappears in this phase. 

5. Cytokinesis – II 

a. Cytokinesis takes place after the nuclear division. 

b. Two haploid cells are formed from each haploid cell. 

c. Thus, four haploid daughter cells are formed. 

d. These cells then undergo changes to form gametes.

a. Recombination is exchange of genetic material between paternal and maternal chromosomes during gamete formation. 

b. The points where crossing over takes place is known as chiasmata. 

c. Chromatids acquire new combinations of alleles by physically exchanging segments in crossing-over. 

d. The exchange of genetic material between homologous chromosomes involves accurate breakage and joining of DNA molecules through a complex mechanism. 

e. It is catalyzed by enzymes.

1. Meiosis is known as reductional division. 

2. The number of chromosome is reduced to half, hence, meiosis is known as reductional division.

Meiosis is known as reductional division because the parent cell produces four daughter cells each having half the number of chromosomes present in the parent cell.

In this type of cell division, the number of chromosomes is reduced to half. Hence, this type of cell division is also called reductional division.

Meiosis is also known as Reductional division.

Duplication of DNA occurs in S-phase. 

i. The diagram shown is of Metaphase. 

A: Chromosomes arranged on metaphase plate

ii. The diagram shown is of Anaphase. B: Chromatids moving to opposite poles.

Karyokinesis is the nuclear division which is divided into prophase, metaphase, anaphase and telophase.

1. Prophase: 

a. In this phase, condensation of chromatin material, migration of centrioles, appearance of mitotic apparatus and disappearance of nuclear membrane takes place. 

b. Due to condensation, each chromosome with its sister chromatids connected by centromere is clearly visible under light microscope. 

c. The nucleolus starts to disappear. 

d. Centrosome start moving towards the opposite poles of the cell. 

e. Mitotic apparatus is almost completely formed. 

2. Metaphase: 

a. Chromosomes are completely condensed and appear short. 

b. Centromere and sister chromatids become very prominent.

c. All the chromosomes are arranged at equatorial plane of cell. This is called metaphase plate. 

d. Mitotic spindle is fully formed in this phase. 

e. Centromere of each chromosome divides horizontally into two, each being associated with a chromatid. 

[Note: The centromeres divide at the beginning of anaphase so that the two chromatids of each chromosome become separated from each other. Source: Cell Division, Donald B. McMillan, Richard J. Harris, in An Atlas of Comparative Vertebrate Histology, 2018.] 

3. Anaphase: 

a. In this phase, chromatids of each chromosome separate and form two chromosomes called daughter chromosomes. 

b. The chromosomes which are formed are pulled away in opposite direction by spindle apparatus. 

c. Anaphase ends when each set of chromosomes reach at opposite poles of the cell. 

4. Telophase: 

a. This is the final stage of karyokinesis. 

b. The chromosomes with their centromeres begin to uncoil at the poles. 

c. The chromosomes lengthen and lose their individuality. 

d. The nucleolus reappears and the nuclear membrane appear around the chromosomes. 

e. Spindle fibres breakdown and get absorbed in the cytoplasm. Thus, two daughter nuclei are formed. 

These are small disc-shaped structures at the surface of the centromeres which serve as the sites of attachment of spindle fibres to the chromosomes.

Steps in mitosis are Karyokinesis and Cytokinesis.

Karyokinesis includes four stages – Prophase, Metaphase, Anaphase and Telophase.

The structure is responsible for initiating cell division in animal cells Centrioles.

Centriole (Centrosome).

The gametes are produced as a result of meiosis hence they have haploid number of chromosomes.

Karyokinesis is the nuclear division which is divided into prophase, metaphase, anaphase and telophase.

1. Prophase: 

a. In this phase, condensation of chromatin material, migration of centrioles, appearance of mitotic apparatus and disappearance of nuclear membrane takes place. 

b. Due to condensation, each chromosome with its sister chromatids connected by centromere is clearly visible under light microscope. 

c. The nucleolus starts to disappear. 

d. Centrosome start moving towards the opposite poles of the cell. 

e. Mitotic apparatus is almost completely formed. 

2. Metaphase: 

a. Chromosomes are completely condensed and appear short. 

b. Centromere and sister chromatids become very prominent. 

c. All the chromosomes are arranged at equatorial plane of cell. This is called metaphase plate. 

d. Mitotic spindle is fully formed in this phase. 

e. Centromere of each chromosome divides horizontally into two, each being associated with a chromatid. 

[Note: The centromeres divide at the beginning of anaphase so that the two chromatids of each chromosome become separated from each other. Source: Cell Division, Donald B. McMillan, Richard J. Harris, in An Atlas of Comparative Vertebrate Histology, 2018.] 

3. Anaphase: 

a. In this phase, chromatids of each chromosome separate and form two chromosomes called daughter chromosomes. 

b. The chromosomes which are formed are pulled away in opposite direction by spindle apparatus. 

c. Anaphase ends when each set of chromosomes reach at opposite poles of the cell. 

4. Telophase: 

a. This is the final stage of karyokinesis. 

b. The chromosomes with their centromeres begin to uncoil at the poles. 

c. The chromosomes lengthen and lose their individuality. 

d. The nucleolus reappears and the nuclear membrane appear around the chromosomes. 

e. Spindle fibres breakdown and get absorbed in the cytoplasm. Thus, two daughter nuclei are formed. 

These are small disc-shaped structures at the surface of the centromeres which serve as the sites of attachment of spindle fibres to the chromosomes. 

The three significant changes that occur in a cell during interphase are:

(i) The cell grows in size.

(ii) New DNA is synthesized as per the old DNA templet.

(iii) Synthesis of RNA and protein takes place.

Chromosome number of a cell is almost doubled up during S – phase

During cell division karyo kinesis (division of nucleus) is followed by the division of cytoplasm. It is called cytokinesis. Or in other words cytokinesis is the division of cytoplasm.

20 meiotic divisions are necessary for formation of 80 sperms.

Colchicine is an alkaloid obtained from Autumn crocus (Colchicum autumnal e). It inhibits the formation of mitotic spindle. As a result, chromosomes duplicate but they remain within the same cell, increasing in number (endoduplication). Such cells are called polyploid cells.

Its advantage is that plant breeders have used colchicine-induced polyploidy as a means of producing variants of agricultural and horticultural crops.

The correct answer is (B) 31

(i) It helps to maintain linear heredity of an organism by keeping the chromosome number constant in daughter cells.

(ii) It helps in development of organism from zygotic stage to adult stage.

(iii) It is the means of repair and regeneration of cells.

(iv) Asexual reproduction is accomplished only through mitosis.

(v) Details of mitosis are similar in all organisms which emphasizes the unity of life.

The correct answer is (C) 32

The correct answer is (C) reductional division

The meiosis is referred to as reduction division because the number of chromosomes in the daughter cells is half than that of the mother cell.

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