List the main differences between mitosis and meiosis?

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).

Explain the stages of prophase I of meiosis.

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.

What is the significance of meiosis?

Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells.The significance of meiosis is in-Formation of gametes − Meiosis form gametes that are essential for sexual reproduction.Genetic information − Meiosis switches on the genetic information for the development of gametes.Crossing over − It introduces new combination of traits or variations.Mutation − Mutations take place due to irregularities of meiotic division.

What will be the amount of DNA in meiosis II products, if meiocyte contains 30 pg DNA in G phase?

30 pg DNA in G phase is doubled during the S phase of the cell cycle by replication to 60 pg.After meiosis, I, DNA content (60 pg) is equally divided into two cells i.e. 30 pg in each cell. Both the cells further divide to form four haploid cells during meiosis II so that the DNA content (30 pg per cell) is further reduced by half i.e. 15 pg DNA in each cell (meiosis II products).So the correct answer is '15 pg'.

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

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.

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.

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

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.

Correct Option: C Explanation: In bivalent condition, there are two chromosomes present with their homologous pair.So, 8 bivalents in metaphase I contains 16 chromosomes.Meiosis I is a reduction division and therefore the number of chromosomes is halved to 8 chromosomes.Meiosis II is an equational division and therefore the number of chromosomes remains same, that is, 8 chromosomes. Hence, if the number of bivalents is 8 in metaphase I, the number of chromosomes in daughter cells after meiosis I and meiosis II respectively will be 8 and 8.

Distinguish anaphase of mitosis from anaphase I of meiosis.

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.

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

Answer in details.With the help of suitable diagrams, explain the five stages of prophase-I of meiosis.

Prophase I is the longest phase of meiosis and is further sub divided into 5 phases:Leptotene : Condensation makes chromosomes become distinct and compact.Zygotene : Homologous chromosome start pairing together by a process called synapsis to form a complex structure called synaptonemal complex. Two synapsed homologous chromosomes form a complex called bivalent or tetrad.Pachytene : Longest phase of prophase IRecombination nodules appear in this stage at the sites where crossing over has to take place between non-sister chromatids of homologous chromosomes.Diplotene : Synaptonemal complex dissolves and recombinants separate from each other except at crossover sites to form X-shaped structure called chiasmata.Diakinesis : Chiasmata terminalises and chromosomes condense. Meiotic spindle assembles and nucleolus and nuclear envelope disappear.

Meiosis II | Definition, Examples, Diagrams

definition

Significance of meiosis

It maintains the same chromosome number in the sexually reproducing organisms.
It provides a way for mixing up of genes, which occurs in two ways: the maternal and paternal chromosomes gets mixed up and cross joining.

definition

Significance of meiosis

1. It maintains the same chromosome number in the sexually reproducing organisms. From a diploid cell, haploid gametes are produced which in turn fuse to form a diploid cell.

2. It restricts the multiplication of chromosome numbers and maintains the stability of the species.

3. Maternal and paternal genes get exchanged during crossing over. It results in variations among the offspring.

4. All the four chromatids of a homologous pair of chromosomes segregate and go over separately to four different daughter cells. This leads to variation in the daughter cells genetically.

definition

Meiosis 2

Phases of Meiosis II

The second meiotic division is very much similar to mitosis. It has the following steps:

1. Prophase II

The events of prophase II are similar to mitotic prophase.
Nucleolus and nuclear membrane disappear.
Spindle fibres are formed at each pole.

2. Metaphase II

Chromosomes move to the centre of the equatorial plane.

They get attached to spindle fibres centromere.

3. Anaphase II

The sister chromatids separate from one another and are pulled to opposite poles of the spindle due to the contraction of the spindle fibres.

4. Telophase II

The chromosomes begin to uncoil and become thin.
They reorganize into the nucleus with the reappearance of the nucleolus and nuclear membrane in each pole.
Cytokinesis follows and four haploid daughter cells are formed and thus the meiotic division is completed.

Meiosis II

definition

Significance of meiosis

definition

Significance of meiosis

definition

Meiosis 2

REVISE WITH CONCEPTS

Meiosis and its Significance

Meiosis I

Quick Summary With Stories

Explanation about Homotypic division

List the main differences between mitosis and meiosis?

Explain the stages of prophase I of meiosis.

What is the significance of meiosis?

What will be the amount of DNA in meiosis II products, if meiocyte contains 30 pg DNA in G phase?

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

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.

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.

Distinguish anaphase of mitosis from anaphase I of meiosis.

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

Answer in details.
With the help of suitable diagrams, explain the five stages of prophase-I of meiosis.