Distinguish between

Question 15 Marks

Some cells do not have gap phase in their cell cycle whereas some cells spend maximum part of their life in gap phase. Search for such cells. Some cells are said to be in $G0$ phase. What is this $G0$ phase?

Answer

$G_0$ is the phase of the cell cycle in eukaryotes in which many cell types stop dividing. It is also called a quiescent stage.
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 $G_0$ phase.
Mature neurons and muscle cells remain in $G_0$ phase.

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Question 25 Marks

meiosis – I and meiosis – II

Answer

Meiosis I	Meiosis II
(a) Diploid cell is divided into two haploid cells.	Two haploid cells formed in meiosis I divides further into four haploid cells.
(b) This division is called heterotypic division.	This division is called homotypic (equational) division.
(c) It consists of prophase – I, metaphase – I, anaphase -1, telophase -1 and cytokinesis.	It consists of prophase – II, metaphase – II, anaphase – II, telophase – II and cytokinesis.
(d) Number of chromosomes is reduced to half, i.e. from diploid to haploid state.	In meiosis II number of chromosomes remain the same.
(e) It is complicated and long duration division.	It is simple and short duration division.
(f) Telophase I results into 2 daughter cells.	Telophase II results in 4 daughter cells.

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Question 35 Marks

mitosis and meiosis

Answer

Mitosis	Meiosis
(a) It occurs in somatic cells and stem cells.	It occurs in germ cells.
(b) In this nucleus divides only once.	In this nucleus divides twice (Meiosis I and Meiosis II)
(c) In these two daughter cells are formed.	In these four daughter cells are formed.
(d) Daughter cells formed by mitotic division are diploid (2n).	Daughter cells formed by meiotic division are haploid (n) •
(e) In mitosis, crossing over does not take place.	In meiosis, crossing over takes place.
(f) Mitosis plays an important role in growth, repair, healing and development.	Meiosis is important for formation of haploid gametes and spores.

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Question 45 Marks

Column I (Phases)	Column II (Their events)
1. Leptotene	(a) Crossing over
2. Zygotene	(b) Desynapsis
3. Pachytene	(c) Synapsis
4. Diplotene	(d) Bouquet stage

Answer

Column I (Phases)	Column II (Their events)
1. Leptotene	(d) Bouquet stage
2. Zygotene	(c) Synapsis
3. Pachytene	(a) Crossing over
4. Diplotene	(b) Desynapsis

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Question 55 Marks

mitosis and meiosis.

Answer

Mitosis	Meiosis
(a) It occurs in somatic cells and stem cells.	It occurs in germ cells.
(b) In this nucleus divides only once.	In this nucleus divides twice (Meiosis I and Meiosis II)
(c) In these two daughter cells are formed.	In these four daughter cells are formed.
(d) Daughter cells formed by mitotic division are diploid (2n).	Daughter cells formed by meiotic division are haploid (n)•
(e) In mitosis, crossing over does not take place.	In meiosis, crossing over takes place.
(f) Mitosis plays an important role in growth, repair, healing and development.	Meiosis is important for formation of haploid gametes and spores.

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Question 65 Marks

Differentiate between anaphase of mitosis and anaphase – I of meiosis.

Answer

Anaphase of mitosis	Anaphase – I of meiosis
1. Centromere divides into two, resulting in the separation of chromatids.	Centromere does not divide.
2. Homologous chromosomes are not involved.	Homologous chromosomes are involved.
3. Disjunction does not occur.	Disjunction occurs.
4. Same number of chromosomes gather at each pole.	Half the chromosome number gather at respective pole.

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