Meiosis Questions in English

(C) During the $zygotene$ stage of $prophase-I$ of meiosis,homologous chromosomes start pairing together. This process of association is known as $synapsis$. Such paired chromosomes are called homologous chromosomes. These pairs are also referred to as bivalents or tetrads.

(C) In meiosis-$I$,specifically during Anaphase-$I$,the homologous chromosomes separate and move towards opposite poles of the cell.
However,the sister chromatids remain attached to each other at their centromeres throughout this process.
In contrast,during Anaphase-$II$,the centromeres split,and the sister chromatids separate.
Therefore,the correct stage where homologous chromosomes separate while sister chromatids remain associated is Anaphase-$I$.

(C) Genetic variation in sexually reproducing organisms is primarily caused by the process of $Crossing over$.
$Crossing over$ occurs during the $Pachytene$ stage of $Prophase-I$ of $Meiosis$.
During this process, non-sister chromatids of homologous chromosomes exchange genetic material, resulting in new combinations of genes (recombination).
$Synapsis$ is the pairing of homologous chromosomes, while $Crossing over$ is the actual exchange of segments that leads to variation.

(B) Meiosis is a type of cell division that reduces the number of chromosomes by half in the daughter cells compared to the parent cell.
During meiosis,the genetic material undergoes recombination (crossing over) and independent assortment,which leads to genetic variation.
Therefore,the genetic composition of the daughter cells produced in meiosis is different from that of the parent cell.

(C) Meiosis is a type of cell division that reduces the chromosome number by half, resulting in the production of haploid gametes.
It occurs specifically in germ cells or reproductive cells.
Among the given options, the $Pollen$ mother cell $(PMC)$ is a diploid cell found in the anther of flowering plants that undergoes meiosis to produce haploid microspores (pollen grains).
Root apex, shoot apex, and leaf apex are parts of the vegetative body (somatic cells) and undergo mitosis for growth and development.

(A) Germ cells (or gamete mother cells) undergo $Meiosis$ to produce gametes. $Meiosis$ is a reductional division where the chromosome number is reduced to half,ensuring that the diploid number is restored upon fertilization. Therefore,the correct answer is $Meiosis$.

(A) Meiosis is a specialized type of cell division that reduces the chromosome number by half.
It involves two successive nuclear and cytoplasmic divisions,known as Meiosis-$I$ and Meiosis-$II$.
In Meiosis-$I$,the homologous chromosomes separate,and in Meiosis-$II$,the sister chromatids separate.
As a result,a single diploid $(2n)$ parent cell undergoes two rounds of division to produce four genetically distinct haploid $(n)$ daughter cells.

(C) Statement $S$ is true because meiosis is the specialized type of cell division that reduces the chromosome number by half,resulting in the production of haploid gametes (reproductive cells).
Reason $R$ is false because,in meiosis,the genetic material $(DNA)$ replicates only once during the $S$-phase of interphase,while the cell undergoes two successive nuclear and cytoplasmic divisions (meiosis $I$ and meiosis $II$). Therefore,the correct answer is $C$.

(A) Meiosis is a type of cell division that reduces the chromosome number by half, resulting in the production of four haploid daughter cells from a single diploid parent cell.
This process involves two successive nuclear divisions, known as Meiosis-$I$ and Meiosis-$II$, but only one round of $DNA$ replication.
Therefore, one cell undergoing meiosis produces $4$ genetically distinct daughter cells.

(B) Meiosis is a type of cell division that reduces the chromosome number by half,resulting in four haploid daughter cells.
It consists of two successive nuclear divisions known as Meiosis-$I$ and Meiosis-$II$.
In Meiosis-$I$,the homologous chromosomes separate,reducing the chromosome number to half.
In Meiosis-$II$,the sister chromatids separate,similar to mitosis.
Therefore,karyokinesis (nuclear division) occurs twice during the entire process of meiosis.

(B) Interkinesis is the stage between meiosis $I$ and meiosis $II$.
It is a short-lived phase.
During interkinesis,there is no replication of $DNA$.
Chromosomal $DNA$ replication occurs during the $S$-phase of interphase,which precedes meiosis $I$.
Therefore,the statement that 'Replication of chromosomal $DNA$ occurs during interkinesis' is incorrect.

(D) bivalent is a pair of homologous chromosomes formed during the $Zygotene$ stage of $Prophase-I$ of meiosis.
Each chromosome in the pair consists of two sister chromatids.
Since a bivalent consists of two homologous chromosomes,and each chromosome has two chromatids,the total number of chromatids in a bivalent is $2 \times 2 = 4$.
These four chromatids are collectively referred to as a tetrad.
Therefore,a bivalent consists of two chromosomes,each having two chromatids,resulting in a total of four chromatids.

(D) The $Pachytene$ stage is the third stage of $Prophase-I$ in $Meiosis-I$.
During this stage,the process of crossing over occurs between non-sister chromatids of homologous chromosomes.
This process is facilitated by the appearance of recombination nodules at the sites where crossing over occurs.
While synapsis (pairing of homologous chromosomes) begins in the $Zygotene$ stage,the bivalents or tetrads become clearly visible during the $Pachytene$ stage.
Therefore,both the appearance of recombination nodules and the clear visibility of tetrads are characteristic events of the $Pachytene$ stage.

(A) Meiosis is a type of cell division that reduces the chromosome number by half.
Like mitosis,meiosis is preceded by an interphase stage.
During the $S$-phase (Synthesis phase) of this interphase,the $DNA$ replication occurs.
This interphase occurs before meiosis $I$.
Meiosis $II$ is similar to mitosis but is not preceded by a $DNA$ replication phase (interphase).
Therefore,the replication of genetic material occurs only during the interphase before meiosis $I$.

(C) The stage between Meiosis-$I$ and Meiosis-$II$ is known as Interkinesis.
It is a short-lived resting phase.
During Interkinesis,there is no replication of $DNA$.
However,the cell may undergo some growth and synthesis of proteins and $RNA$.
Therefore,the correct option is $C$.

(A) In Metaphase $II$ of meiosis,the chromosomes align at the equatorial plate. Each chromosome consists of two sister chromatids. The kinetochores of the sister chromatids are attached to spindle fibers from opposite poles. Therefore,each chromosome is attached to spindle fibers from both poles.

(A) In $Anaphase-I$ of meiosis,the homologous chromosomes separate,while the sister chromatids remain associated at their centromeres.
In $Anaphase-II$,the centromeres split,and the sister chromatids (now individual chromosomes) move toward opposite poles.
Therefore,the primary difference is the separation of homologous chromosomes in $Anaphase-I$ versus the splitting of centromeres in $Anaphase-II$.

(A) During the diplotene stage of prophase-$I$ of meiosis,the synaptonemal complex dissolves,causing the homologous chromosomes to separate from each other except at the sites of crossovers.
These $X$-shaped structures are called chiasmata.
Therefore,the statement $A$ is true because the chromosomes move away from each other due to the dissolution of the synaptonemal complex.
Statement $R$ is also true because the chiasmata (the sites of crossing over) hold the homologous chromosomes together,preventing complete separation at this stage.
Thus,$R$ provides the correct explanation for why the chromosomes remain connected despite moving apart.

(B) Assertion $A$ is true because meiosis is a specialized type of cell division that reduces the chromosome number by half,which is only possible in diploid $(2n)$ cells to produce haploid $(n)$ gametes.
Reason $R$ is also true because during meiosis-$I$,the homologous chromosomes separate,resulting in the reduction of the chromosome number from diploid to haploid,hence it is called reductional division.
However,the reason $R$ explains why meiosis is a reductional division,but it does not directly explain why meiosis is restricted to diploid cells. Therefore,$R$ is not the correct explanation of $A$.

(B) The given figure shows two successive rounds of nuclear and cytoplasmic division,resulting in four daughter cells from a single parent cell.
This is the characteristic feature of meiosis,where a diploid cell undergoes two divisions (Meiosis-$I$ and Meiosis-$II$) to produce four haploid daughter cells.
In the figure,$M$ represents Meiosis-$I$ and $N$ represents Meiosis-$II$.

(C) The provided figure illustrates the process of meiosis.
$M$ represents meiosis-$I$ and $N$ represents meiosis-$II$.
In meiosis-$I$,homologous chromosomes pair up and undergo recombination (crossing over) during prophase-$I$.
Cell $P$ is in the prophase-$I$ stage of meiosis-$I$,where the process of recombination occurs between homologous chromosomes.
Therefore,the correct process occurring in cell $P$ is recombination.

(B) The provided figure represents the process of meiosis.
Meiosis $I$ $(M)$ is a reductional division where the diploid parent cell divides into two haploid daughter cells.
Cell $P$ represents the end of Meiosis $I$ (or late anaphase/telophase $I$),and cell $Q$ represents the two daughter cells formed after the completion of Meiosis $I$.
Since Meiosis $I$ reduces the chromosome number to half,the cells formed at stage $Q$ are haploid $(n)$.

(B) The provided figure illustrates the process of meiosis.
$M$ represents meiosis-$I$,where the homologous chromosomes separate.
$N$ represents meiosis-$II$,which is similar to mitosis.
Specifically,the cell labeled $R$ is undergoing meiosis-$II$,where sister chromatids separate,resulting in the formation of haploid daughter cells.

(C) The provided figure illustrates the process of meiosis.
Meiosis is divided into two stages: Meiosis $I$ and Meiosis $II$.
In Meiosis $I$,homologous chromosomes separate,resulting in two haploid daughter cells. This is represented by the section labeled $M$.
Meiosis $II$ involves the separation of sister chromatids,similar to mitosis,resulting in four haploid daughter cells,which is represented by the section labeled $N$.
Therefore,the part labeled $M$ represents Meiosis $I$.

(A) The provided figure illustrates the process of meiosis.
Meiosis is divided into two main stages: Meiosis $I$ and Meiosis $II$.
The part labeled $M$ represents Meiosis $I$,where the homologous chromosomes separate,resulting in two haploid daughter cells.
The part labeled $N$ represents Meiosis $II$,which is similar to mitosis. In this stage,the sister chromatids separate,and the two haploid cells formed in Meiosis $I$ divide further to produce four haploid daughter cells.
Therefore,the part labeled $N$ indicates Meiosis $II$.

(B) The given figure shows the chromosomes appearing as thin,thread-like structures within the nucleus. This characteristic appearance,where chromosomes begin to condense and become visible as long,thin threads,is the hallmark of the Leptotene stage of Prophase $I$ in meiosis. During this stage,the chromosomes are not yet fully condensed,and the pairing of homologous chromosomes (synapsis) has not yet occurred,which distinguishes it from the subsequent Zygotene stage.

(D) Meiosis is a specialized type of cell division that reduces the chromosome number by half,resulting in the production of haploid daughter cells.
$1$. It occurs during the formation of gametes (gametogenesis) in sexually reproducing organisms.
$2$. During the cell cycle,$DNA$ replication occurs only once during the $S$-phase of interphase,preceding the two successive nuclear divisions (Meiosis $I$ and Meiosis $II$).
$3$. The cell undergoes two successive divisions,resulting in four daughter cells.
Therefore,all the given statements are correct.

(D) In Meiosis-$I$,Prophase-$I$ is divided into five sub-stages: Leptotene,Zygotene,Pachytene,Diplotene,and Diakinesis.
$1$. Leptotene: Chromosomes appear as thin,thread-like structures.
$2$. Zygotene: Homologous chromosomes pair up,a process known as synapsis.
$3$. Pachytene: Crossing over occurs between non-sister chromatids of homologous chromosomes. Chiasmata are $X$-shaped structures that become visible during the next stage,Diplotene.
$4$. Diplotene: The chiasmata become clearly visible as the homologous chromosomes begin to separate. The formation of the bipolar spindle typically occurs during Prometaphase or Metaphase,not Diplotene.
Therefore,the pair 'Formation of chiasmata - Pachytene' is technically mismatched because chiasmata are the physical manifestation of crossing over that becomes visible in Diplotene,and 'Formation of bipolar spindle - Diplotene' is also incorrect as it occurs later.

(B) During the process of synapsis in Prophase-$I$ of Meiosis,homologous chromosomes pair up to form a bivalent or tetrad.
Each chromosome consists of two sister chromatids.
Since a bivalent consists of two homologous chromosomes,and each chromosome has two chromatids,the total number of chromatids in a bivalent is $2 + 2 = 4$.
Therefore,each chromosome involved in synapsis contains $2$ chromatids.

(A) During the process of meiosis,specifically in the pachytene stage of prophase-$I$,homologous chromosomes pair up to form a structure called a bivalent or tetrad.
Each chromosome consists of two sister chromatids.
Since a bivalent is composed of two homologous chromosomes,and each chromosome has two chromatids,the total number of chromatids in a bivalent is $2 + 2 = 4$.
Therefore,a bivalent is also known as a tetrad because it contains four chromatids.

(B) Meiosis is a reductional division that occurs in two stages: Meiosis-$I$ and Meiosis-$II$.
During Anaphase-$I$,the homologous chromosomes separate and move to opposite poles,while the sister chromatids remain attached at the centromere.
As a result,each pole receives only half the number of chromosomes compared to the parent cell.
Therefore,the reduction in chromosome number from diploid $(2n)$ to haploid $(n)$ is completed during Anaphase-$I$.

(B) During $Meiosis-II$,the $Anaphase-II$ stage is characterized by the splitting of the centromere of each chromosome.
This allows the sister chromatids to separate and move towards opposite poles of the cell.
This process is similar to the $Anaphase$ of $Mitosis$.
Therefore,the correct statement is that sister chromatids separate due to the splitting of the centromere.

(B) The figure shows the pairing of homologous chromosomes,a process known as synapsis.
This pairing of homologous chromosomes is the characteristic feature of the Zygotene stage of Prophase-$I$ of meiosis.
During this stage,the formation of synaptonemal complexes occurs between the homologous chromosomes.

(C) The figure shows homologous chromosomes that have undergone crossing over,as evidenced by the exchange of segments between non-sister chromatids. Crossing over is the characteristic feature of the Pachytene stage of Prophase-$I$ in Meiosis. During this stage,the bivalent chromosomes clearly appear as tetrads,and the recombination nodules facilitate the exchange of genetic material.

(A) The correct matching is as follows:
$(A)$ Pachytene: During this stage, crossing-over occurs between non-sister chromatids of homologous chromosomes $(iii)$.
$(B)$ Metaphase-$I$: During this stage, the bivalent chromosomes align at the equatorial plate $(iv)$.
$(C)$ Diakinesis: This is the final stage of meiotic prophase-$I$, characterized by the terminalisation of chiasmata $(ii)$.
$(D)$ Zygotene: During this stage, the pairing of homologous chromosomes occurs, known as synapsis $(i)$.
Thus, the correct sequence is $A-(iii), B-(iv), C-(ii), D-(i)$.

(B) : Synapsis is the process of pairing of homologous chromosomes. It occurs specifically during the zygotene stage of prophase $I$ of meiosis. This phenomenon is not observed during mitosis,as mitosis involves the division of somatic cells without the pairing of homologous chromosomes.

(C) : Crossing over is a process of exchange of genetic material or chromatid segments between two homologous chromosomes. It is initiated during the pachytene stage of meiosis $I$.

(D) The correct sequence is $(ii), (i), (iii), (iv)$.
Prophase-$I$ of meiosis is divided into five sub-stages: Leptotene,Zygotene,Pachytene,Diplotene,and Diakinesis.
$(ii)$ Synapsis (pairing of homologous chromosomes) occurs during the Zygotene stage.
$(i)$ Crossing over (exchange of genetic material between non-sister chromatids) occurs during the Pachytene stage.
$(iii)$ Terminalisation of chiasmata (shifting of chiasmata towards the ends of chromosomes) occurs during the Diakinesis stage.
$(iv)$ Disappearance of the nucleolus also occurs during the Diakinesis stage,marking the end of Prophase-$I$.

(A) The $Pachytene$ stage is characterized by the appearance of recombination nodules,which are the sites where crossing over occurs between non-sister chromatids of homologous chromosomes.
These nodules contain a multienzyme complex known as $Recombinase$.
$Recombinase$ is composed of various enzymes such as endonuclease,exonuclease,unwindase,and $R$-protein,which facilitate the exchange of genetic material.

(A) During the $zygotene$ stage of $Meiosis-I$,homologous chromosomes start pairing together,a process known as $synapsis$.
These paired chromosomes are referred to as homologous chromosomes.
The electron micrographs of this stage reveal that the pairing is accompanied by the formation of a complex structure known as the $synaptonemal$ $complex$.
The complex formed by a pair of synapsed homologous chromosomes is specifically called a $bivalent$ or a $tetrad$.

(A) The correct answer is $A$.
During the $zygotene$ stage of prophase $I$ of meiosis,the chromosomes begin to pair up.
This process of pairing of homologous chromosomes is known as $synapsis$.
Each pair of homologous chromosomes is referred to as a $bivalent$ or a $tetrad$.

(C) The correct answer is $C$.
During gamete formation,the enzyme recombinase participates during the pachytene stage of prophase $I$.
This stage is characterized by the appearance of recombination nodules,which are the sites where crossing over occurs between non-sister chromatids of homologous chromosomes.
Crossing over is the exchange of genetic material between two homologous chromosomes.
Crossing over is an enzyme-mediated process,and the enzyme involved in this process is called recombinase.

(A) The given figure shows crossing over,$i.e.$,the exchange of genetic segments between two non-sister chromatids of homologous chromosomes.
Crossing over is a characteristic feature of meiosis and occurs specifically during the pachytene stage of prophase $I$.

(C) During $Anaphase I$,the homologous chromosomes of each bivalent (tetrad) separate and move toward opposite poles of the cell.
In this stage,the sister chromatids remain associated at their centromeres,meaning the centromeres do not split.
This process ensures that each pole receives only one chromosome from each homologous pair,effectively reducing the chromosome number by half.
In contrast,during $Anaphase II$,the centromeres split and sister chromatids separate.

(C) The correct answer is $C$.
During the $zygotene$ or $zygonema$ stage of meiotic $prophase-I$, the chromosomes become shorter and thicker.
The homologous chromosomes come to lie side-by-side in pairs.
This pairing of homologous chromosomes is known as $synapsis$ or $syndesis$.
$A$ pair of homologous chromosomes lying together is called a $bivalent$.

(C) Meiosis is a type of cell division that reduces the chromosome number by half.
In the process of spermatogenesis,the $2n$ primary spermatocytes undergo Meiosis-$I$ to form two haploid $(n)$ secondary spermatocytes.
These secondary spermatocytes then undergo Meiosis-$II$ to form spermatids,which eventually differentiate into mature sperm.
Therefore,Meiosis-$I$ occurs in primary spermatocytes and Meiosis-$II$ occurs in secondary spermatocytes.
Thus,both primary and secondary spermatocytes are involved in the process of meiosis.

(A) Synapsis is the pairing of homologous chromosomes that occurs during the $Zygotene$ stage of $Prophase-I$ in meiosis.
During this stage,chromosomes start pairing together,and this process of association is called synapsis.
Such paired chromosomes are called homologous chromosomes.
$Leptotene$ is the stage where chromosomes become visible.
$Diakinesis$ is the final stage of meiotic prophase $I$ where terminalization of chiasmata occurs.
$Interphase$ is the phase between two successive cell divisions.

(A) In Telophase-$I$,the nuclear membrane and nucleolus reappear,and the chromosomes undergo some decondensation. This is a correct description of the phase.
In Anaphase-$II$,the centromeres split and sister chromatids move towards opposite poles,not alignment at the equator.
In Metaphase-$II$,chromosomes align at the equator,not the splitting of the centromere.
In Prophase-$II$,the nuclear membrane disappears and chromosomes condense,not the movement of chromatids to poles.

(A) The provided figure shows homologous chromosomes pairing up and forming bivalents or tetrads.
This pairing process,known as synapsis,is a characteristic feature of the prophase stage of meiosis $- I$.
Specifically,it occurs during the zygotene sub-stage of prophase $- I$.
Therefore,the correct identification for the given figure is prophase $- I$.