Question 1

List the main differences between mitosis and meiosis?

Accepted Answer

Answer-Mitosis Meiosis1) This division takes place in somatic cells and as a result of this division, growth occurs.  1) This takes place usually in reproductive cells and as a result of this character one generation pass into the other.2) Completed in one stage. 2) Completed in two stages.3) Prophase is smaller (as compared to prophase of Meiosis). 3) Prophase longer than prophase of mitosis and divided into five substages. 4) Crossing over does not take place. 4) Crossing over takes place in which the exchange of segments of chromatids occurs. 5) Synapsis does not take place at metaphase. 5) Synapsis between homologous chromosomes takes place (bivalent stage). 6) At metaphase, the centromere is towards the equatorial plate and ends of chromosomes towards poles. Centromere divides. 6) At metaphase I, the centromere is towards poles and ends of chromosomes towards the equatorial plate. Centromere does not divide. 7) Chromatids are long and thin.7) Chromatids are shorter and thick  8) Cytokinesis follows karyokinesis. 8) After Telophase I, cytokinesis does not take place always (may occur).

Question 2

What is the significance of meiosis?

Accepted Answer

Meiosis is the process by which sexually reproducing organisms make their sex cells, sperm and eggs. During meiosis, a specialized cell called a germ cell splits to make four new sex cells, each with half the number of chromosomes as the original germ cell.The significance of meiosis are as follows:-Formation of gametes &#8722; Meiosis form gametes that are essential for sexual reproduction.Genetic information &#8722; Meiosis switches on the genetic information for the development of gametes.Maintenance of chromosome number &#8722; Meiosis maintains the fixed number of chromosomes in sexually reproducing organisms.Assortment of chromosomes &#8722; In meiosis paternal and maternal chromosomes assort independently. It causes reshuffling of chromosomes and the traits controlled by them.Crossing over &#8722; It introduces new combination of traits or variations.Mutation &#8722; Mutations take place due to irregularities of meiotic division.

Question 3

Explain the stages of prophase I of meiosis.

Accepted Answer

The prophase I of meiosis occurs in the following stages:1. Leptotene- This phase is the start of prophase-I. It is marked by the condensation of the chromosomes.2. Zygotene- In this phase the homologous chromosomes start pairing up, called the synapsis. The synaptonemal complex starts building up. This complex is required to hold the homologous chromosomes at a place close to each other. Bivalent chromosomes are visible at this stage.3. Pachytene- In this stage, this non-sister chromatids of homologous chromosomes exchange their parts, the process is called the crossing over. The attachment point of the crossing-over of the non-sister chromatids is called chiasma.4. Diplotene- The crossing-over process is completed by this stage. The homologous chromosomes remain attched at the point of chiasma.5. Diakinesis- The homologous chromosomes start to separate and synaptonemal complex disappears. The nuclear membrane also disappears.

Question 4

Name the stage of cell cycle at which one of the following events occur.
(i) Chromosomes are moved to spindle equator.
(ii) Centromere splits and chromatids separate.
(iii) Pairing between homologous chromosomes takes place.
(iv) Crossing over between homologous chromosomes takes place.

Accepted Answer

(i) Metaphase(ii) Anaphase(iii) Zygotene of meiosis I(iv) Pachytene of meiosis I

Question 5

Arrange the following events of meiosis in correct sequence (a) Crossing over (b) Synapsis (c) Terminalisation of chiasmata (d) Disappearance of nucleolus.

Accepted Answer

Correct Answer: (B) b, a, c, dExplanation:During Meiosis I the first step is synapsis to form the synaptonemal complex.After that crossing over between the homologous chromosome takes place.Then after crossing over terminalisation of chiasmata happens.After that, the nucleolus gets disappeared.Hence, option (B) is the correct sequence of meiosis.

Question 6

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.

Accepted Answer

In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells with half the number of chromosomes as the original parent cell. The two meiotic divisions are known as meiosis I and meiosis II. Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated so that it consists of two identical sister chromatids attached at a centromere. In meiosis I, homologous chromosomes pair with each other and can exchange genetic material in a process called chromosomal crossover. The homologous chromosomes are then pulled apart into two new separate daughter cells, each containing half the number of chromosomes as the parent cell. At the end of meiosis I, sister chromatids remain attached and may differ from one another if crossing-over occurred. In meiosis II, the two cells produced during meiosis I divide again. During this division, sister chromatids detach from one another and are separated into four total daughter cells. These cells can mature into gametes, spores, pollen, and other reproductive cells. So, the chromosome number is decreased in meiosis I and not in meiosis II. So, If the number of bivalents is 8 in metaphase I, the number of chromosomes in daughter cells after meiosis I and meiosis II respectively are 8 and 8.So, the correct answer is option C.

Question 7

Describe the following : (a) Synapsis (b) Bivalent (c) ChiasmataDraw a diagram to illustrate your answer.

Accepted Answer

(a) Synapsis : The pairing of homologous chromosomes is called as synapsis. This occurs during the second stage of prophase I or zygotene.(b) Bivalent : Bivalent or tetrad is a pair of synapsed homologous chromosomes. They are formed during the zygotene stage of prophase I of meiosis.(c) Chiasmata : Chiasmata is the site where two non-sister chromatids have crossed over. It represents the site of cross-over. It is formed during the diplotene stage of prophase I of meiosis.

Question 8

Distinguish anaphase of mitosis from anaphase I of meiosis.

Accepted Answer

Answer-Anaphase of mitosis Anaphase I of meiosis 1. The centromere of every chromosome divides. 1. The centromere do not divide. 2. Separation of sister chromatids takes place. 2. Homologous chromosomes are separated.3. Only one chromatid of every chromosome moves to the pole.  3. Each homologous pair of chromosomes moves to the pole with both the chromatids. 4. The chromatids moving to one pole are genetically identical to those moving to the opposite pole. 4. The chromosomes moving to one pole are not genetically identical to those moving to the opposite pole.

Question 9

Match the column I with column II and select the correct answer.

Accepted Answer

1. The pachytene - At this point a tetrad of the chromosomes has formed known as a bivalent. This is the stage when chromosomal crossover (crossing over) occurs. Non-sister chromatids of homologous chromosomes may exchange segments over regions of homology.2. The zygotene stage - occurs as the chromosomes approximately line up with each other into homologous chromosome pairs. In some organisms, this is called as the bouquet stage because of the way the telomeres cluster at one end of the nucleus. At this stage, the synapsis of homologous chromosomes takes place, facilitated by assembly of central element of the synaptonemal complex. 3. During the diplotene stage, the synaptonemal complex degrades and homologous chromosomes separate from one another a little. The chromosomes themselves uncoil a bit, allowing some transcription of DNA. However, the homologous chromosomes of each bivalent remain tightly bound at chiasmata, the regions where crossing-over occurred. 4. The first stage of prophase I is the leptotene stage. In this stage of prophase I, individual chromosomes each consisting of two sister chromatids condense from the diffuse interphase conformation into visible strands within the nucleus. However, the two sister chromatids are still so tightly bound that they are indistinguishable from one another. 5. During leptotene, lateral elements of the synaptonemal complex assemble. 6. Chromosomes condense further during the diakinesis stage. This is the first point in meiosis where the four parts of the tetrads are actually visible. Sites of crossing over entangle together, effectively overlapping, making chiasmata clearly visible. During this stage terminalization occurs. Thus, option B is correct.

Question 10

Crossing over takes place during which of the following stage?

Accepted Answer

Crossing over takes place during the pachytene stage. During this stage, non-sister chromatids of homologous chromosomes may exchange segments over regions of homology. Sex chromosomes, however, are not wholly identical, and only exchange information over a small region of homology. At the sites where exchange happens, chiasmata form. The exchange of information between the non-sister chromatids results in a recombination of information; each chromosome has the complete set of information it had before, and there are no gaps formed as a result of the process. Because the chromosomes cannot be distinguished in the synaptonemal complex, the actual act of crossing over is not perceivable through the microscope, and chiasmata are not visible until the next stage.

Revise with Concepts

Meiosis and its Significance

Meiosis I

Meiosis II

Learn with Videos

Quick Summary With Stories

Significance of Meiosis

Explanation about Heterotypic Division - Part A

Explanation about Heterotypic Division - Part B

Explanation about Homotypic division

List the main differences between mitosis and meiosis?

What is the significance of meiosis?

Explain the stages of prophase I of meiosis.

Name the stage of cell cycle at which one of the following events occur.
(i) Chromosomes are moved to spindle equator.
(ii) Centromere splits and chromatids separate.
(iii) Pairing between homologous chromosomes takes place.
(iv) Crossing over between homologous chromosomes takes place.

Arrange the following events of meiosis in correct sequence
(a) Crossing over (b) Synapsis (c) Terminalisation of chiasmata (d) Disappearance of nucleolus.

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.

Describe the following :
(a) Synapsis
(b) Bivalent
(c) Chiasmata
Draw a diagram to illustrate your answer.

Distinguish anaphase of mitosis from anaphase I of meiosis.

Match the column I with column II and select the correct answer.

Crossing over takes place during which of the following stage?

Revise with Concepts

Meiosis and its Significance

Meiosis I

Meiosis II

Learn with Videos

Quick Summary With Stories

Significance of Meiosis

Explanation about Heterotypic Division - Part A

Explanation about Heterotypic Division - Part B

Explanation about Homotypic division

List the main differences between mitosis and meiosis?

What is the significance of meiosis?

Explain the stages of prophase I of meiosis.

Name the stage of cell cycle at which one of the following events occur.(i) Chromosomes are moved to spindle equator.(ii) Centromere splits and chromatids separate.(iii) Pairing between homologous chromosomes takes place.(iv) Crossing over between homologous chromosomes takes place.

Arrange the following events of meiosis in correct sequence (a) Crossing over (b) Synapsis (c) Terminalisation of chiasmata (d) Disappearance of nucleolus.

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.

Describe the following : (a) Synapsis (b) Bivalent (c) ChiasmataDraw a diagram to illustrate your answer.

Distinguish anaphase of mitosis from anaphase I of meiosis.

Match the column I with column II and select the correct answer.

Crossing over takes place during which of the following stage?

Name the stage of cell cycle at which one of the following events occur.
(i) Chromosomes are moved to spindle equator.
(ii) Centromere splits and chromatids separate.
(iii) Pairing between homologous chromosomes takes place.
(iv) Crossing over between homologous chromosomes takes place.

Arrange the following events of meiosis in correct sequence
(a) Crossing over (b) Synapsis (c) Terminalisation of chiasmata (d) Disappearance of nucleolus.

Describe the following :
(a) Synapsis
(b) Bivalent
(c) Chiasmata
Draw a diagram to illustrate your answer.