Meiosis Questions in English

(A) Meiosis is a reductional division that occurs in germ cells.
During meiosis-$I$,the homologous chromosomes separate,which reduces the chromosome number to half of the parent cell.
Therefore,the daughter cells produced at the end of meiosis have half the number of chromosomes compared to the parent cell.

(A) Crossing over is a biological process that produces new combinations of genes by exchanging segments between non-sister chromatids of homologous chromosomes.
It occurs between homologous chromosomes at the four-stranded stage during the pachytene sub-stage of prophase-$I$ of meiosis-$I$.

(C) The stage between two meiotic divisions is called interkinesis.
It is generally short-lived and is followed by prophase-$II$,which is a much simpler prophase than prophase-$I$ of meiosis-$I$.

(C) During $Metaphase-I$ of meiosis,the homologous chromosome pairs,known as tetrads or bivalents,align along the equatorial plate (metaphase plate) of the cell. This alignment is a characteristic feature of $Metaphase-I$ and ensures that homologous chromosomes are properly segregated to opposite poles during the subsequent $Anaphase-I$.

(A) Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction. When a haploid sperm $(n)$ fuses with a haploid egg $(n)$ during fertilization,the resulting zygote is diploid $(2n)$,thereby restoring the original chromosome number.

(D) Meiosis occurs in a diploid cell. It is a double division which gives rise to four haploid cells,each having half the number of chromosomes as compared to the parent cell. The term '$meiosis$' was coined by Farmer and Moore in $1905$.

(A) Synapsis is the process of pairing of homologous chromosomes. This phenomenon occurs during the $Zygotene$ stage of $Prophase-I$ in meiosis. During this phase,chromosomes derived from both parents (maternal and paternal) align and pair up to form bivalents or tetrads.

(A) Meiosis is a specialized type of cell division that reduces the chromosome number by half,resulting in the production of haploid daughter cells.
It specifically occurs in germ cells (also known as meiocytes) to produce gametes (eggs or sperm) for sexual reproduction.
Somatic cells like liver cells undergo mitosis,and most unicellular organisms primarily reproduce via mitosis or binary fission.

(D) Synapsis is the pairing of homologous chromosomes that occurs during the $zygotene$ stage of $prophase-I$ of $meiosis-I$. Since mitosis is a process of equational division that occurs in somatic cells and does not involve the pairing of homologous chromosomes,synapsis is not observed during mitosis.

(A) Meiosis is a reductional division. During Anaphase-$I$,the homologous chromosomes separate and move to opposite poles. As a result,each daughter cell receives only half the number of chromosomes compared to the parent cell. Therefore,the reduction in chromosome number occurs during Anaphase-$I$.

(D) $Meiosis$ is a reductional division that occurs in a diploid cell,resulting in four haploid daughter cells.
During the $Prophase-I$ stage of $Meiosis-I$,homologous chromosomes pair up to form a structure known as a bivalent or tetrad.
$A$ bivalent consists of two homologous chromosomes,where each chromosome is composed of two sister chromatids.
Therefore,a bivalent contains a total of four chromatids and two centromeres.

(D) Pachytene,also known as the thick thread stage,is the third and longest substage of prophase-$I$ of meiosis. It is characterized by the process of crossing over,during which non-sister chromatids of homologous chromosomes twist around each other and exchange genetic segments through the breakage and subsequent fusion of $DNA$ strands.

(A) Meiosis is divided into two stages: Meiosis-$I$ and Meiosis-$II$.
In Meiosis-$I$,the chromosome number is reduced to half,hence it is known as the reductional division.
In Meiosis-$II$,the chromosome number remains the same as in the parent cell,similar to mitosis,hence it is known as the equational division.

(B) Independent Assortment of Chromosomes: The paternal and maternal chromosomes of each homologous pair segregate during Anaphase-$I$ independently of the other chromosomes.
Anaphase-$I$ is the cytological event that corresponds to Mendel's law of independent assortment.
Although the paternal and maternal chromosomes of a homologous pair have the genes for the same traits,either chromosome of a pair may carry different alleles of the same genes.
Therefore,independent assortment of homologous chromosomes in Anaphase-$I$ introduces genetic variability.

(A) Chiasmata are $X$-shaped structures that form between homologous chromosomes during the diplotene stage of prophase-$I$ of meiosis. They represent the sites where crossing over has occurred,which involves the exchange of genetic material between non-sister chromatids of homologous chromosomes. As the synaptonemal complex dissolves,the homologous chromosomes begin to separate but remain attached at these crossover points,known as chiasmata.

(C) During the pachytene substage of prophase-$I$ of meiosis,the non-sister chromatids of homologous chromosomes exchange genetic segments between themselves.
This exchange of chromatid segments is known as crossing over.
Crossing over involves the breakage of $DNA$ strands followed by their fusion with the opposite chromatid,which leads to genetic recombination.

(A) In meiosis,the daughter cells are not genetically similar to the parent cell primarily due to the process of crossing over.
Crossing over involves the mutual exchange of genetic material between non-sister chromatids of homologous chromosomes during the pachytene stage of prophase-$I$ of meiosis.
This process results in new combinations of genes (recombination),leading to genetic variation in the daughter cells.

(D) Meiosis is a reductional division,in which the chromosome number is reduced to half,resulting in haploid cells.
It is primarily observed in reproductive cells during gametogenesis or sporogenesis.
In plants,meiosis occurs in spore mother cells (such as microspore mother cells or megaspore mother cells) to produce haploid spores.
Tapetal cells are somatic cells,while megaspores and microspores are already haploid products of meiosis.

(B) Statement $I$ is correct: Meiosis involves the pairing of homologous chromosomes (synapsis) and recombination (crossing over) between non-sister chromatids.
Statement $II$ is incorrect: Meiosis results in the formation of four haploid daughter cells,not two diploid cells.
Statement $III$ is correct: Meiosis consists of two successive nuclear and cell divisions (meiosis-$I$ and meiosis-$II$) but only one cycle of $DNA$ replication during the $S$-phase.
Statement $IV$ is correct: Meiosis-$I$ begins after the $DNA$ replication in the $S$-phase,which results in the formation of identical sister chromatids.
Therefore,only statement $II$ is incorrect.

(B) The events of meiosis $I$ occur in the following order:
$1.$ $\text{Synapsis}$ $(III)$: Homologous chromosomes pair up during the $\text{Zygotene}$ stage.
$2.$ $\text{Crossing}$ $\text{over}$ $(II)$: Exchange of genetic material between non-sister chromatids occurs during the $\text{Pachytene}$ stage.
$3.$ $\text{Terminalization}$ $(I)$: Chiasmata move towards the ends of the chromosomes during the $\text{Diakinesis}$ stage.
$4.$ $\text{Disjunction}$ $\text{of}$ $\text{genomes}$ $(IV)$: Homologous chromosomes separate during $\text{Anaphase}$ $I$.
Therefore, the correct sequence is $III \rightarrow II \rightarrow I \rightarrow IV$.

(C) The correct option is $C$.
$I.$ In $Anaphase-I$,the homologous chromosomes separate and move to opposite poles,which reduces the chromosome number to half (haploid state) in each daughter cell.
$II.$ In $Anaphase-II$,the sister chromatids separate and move to opposite poles,which reduces the amount of $DNA$ to the haploid state in the resulting gametes.

(D) Meiosis-$I$ is a reductional division where homologous chromosomes separate,reducing the chromosome number to half.
However,each chromosome still consists of two sister chromatids (replicated $DNA$).
Meiosis-$II$ is an equational division similar to mitosis,which is necessary to separate these sister chromatids so that each daughter cell receives a single chromatid (a complete set of unreplicated chromosomes).

(D) Meiosis,also known as reductional division,is a process where one diploid cell divides to form $4$ haploid daughter cells. This process reduces the chromosome number by half in the resulting cells.

(B) In meiosis-$I$,the prophase-$I$ is divided into five sub-stages: Leptotene,Zygotene,Pachytene,Diplotene,and Diakinesis.
During the Leptotene stage,the chromatin fibres begin to condense and coil to form compact chromosomes.
Therefore,the condensation and coiling of chromatin fibres start during the Leptotene stage.

(C) During the pachytene stage of meiosis-$I$,homologous chromosomes pair up to form a bivalent or tetrad.
Each bivalent consists of two homologous chromosomes.
Since each chromosome has already replicated during the $S$-phase,it consists of two sister chromatids.
Therefore,a tetrad (bivalent) contains a total of $4$ chromatids (two from each homologous chromosome).

(A) During Meiosis-$I$,specifically in Anaphase-$I$,the homologous chromosomes separate and move towards opposite poles of the cell.
This process is responsible for the reduction in the number of chromosomes in the daughter cells,which is a hallmark of Meiosis-$I$ (reductional division).
In contrast,during Anaphase-$II$,it is the sister chromatids that separate and move towards opposite poles.

(C) During the pachytene stage of prophase-$I$ of meiosis,crossing over occurs between non-sister chromatids of homologous chromosomes.
Following this,in the diplotene stage,the homologous chromosomes begin to separate from each other except at the sites of crossovers.
These $X$-shaped structures,which mark the sites where crossing over has occurred,are known as chiasmata.

(A) The process of meiosis $I$ is divided into several stages within Prophase-$I$: Leptotene,Zygotene,Pachytene,Diplotene,and Diakinesis.
During the Diplotene stage,the synaptonemal complex dissolves and the homologous chromosomes of the bivalents start to separate from each other except at the sites of crossovers.
These $X$-shaped structures are called chiasmata.
In the final stage of Prophase-$I$,which is Diakinesis,the terminalisation of chiasmata occurs,where the chiasmata move towards the ends of the chromosomes.

(A) During meiosis,homologous chromosomes pair up to form bivalents (or tetrads) during prophase $I$.
These bivalent chromosomes then align themselves at the equatorial plate (metaphase plate) during metaphase $I$.
This alignment is a characteristic feature of metaphase $I$,where spindle fibers from opposite poles attach to the kinetochores of homologous chromosomes.

(B) In the $G_1$ phase,the number of chromosomes is $2n = 30$.
During the $S$ phase,$DNA$ replication occurs,but the number of chromosomes remains the same $(2n = 30)$.
In the zygotene stage of Prophase-$I$ of meiosis,homologous chromosomes pair up to form bivalents (or tetrads).
The number of bivalents is equal to half the number of chromosomes,which is $n$.
Therefore,the number of bivalents = $30 / 2 = 15$.

(C) In the $G_1$ phase,the meiocyte is diploid $(2n)$ and contains $2c$ amount of $DNA$. Given that $2c = 30 \; pg$.
During the $S$ phase,$DNA$ replication occurs,doubling the $DNA$ content to $4c$ $(60 \; pg)$.
After meiosis $I$,two daughter cells are formed,each with $n$ chromosomes and $2c$ amount of $DNA$ $(30 \; pg)$.
After meiosis $II$,each of these cells divides again to form four haploid daughter cells,each containing $n$ chromosomes and $c$ amount of $DNA$.
Since $2c = 30 \; pg$,then $c = 15 \; pg$.
Therefore,the amount of $DNA$ in each meiosis $II$ product is $15 \; pg$.

(D) Meiosis consists of two successive nuclear and cell divisions ($Meiosis-I$ and $Meiosis-II$) with a single cycle of $DNA$ replication.
During $Meiosis-I$,homologous chromosomes segregate,and chiasmata formation occurs during prophase-$I$.
After $Meiosis-II$,both the number of chromosomes and the amount of $DNA$ in the daughter cells are reduced to half compared to the parent cell.
Therefore,the statement that the amount of $DNA$ remains the same after $Meiosis-II$ is incorrect.

(B) Meiosis is a type of cell division that reduces the chromosome number by half. It consists of two successive nuclear divisions:
$1$. Meiosis $I$: This is the reductional division where the chromosome number is halved.
$2$. Meiosis $II$: This is the equational division,similar to mitosis,where the chromosome number remains the same as the daughter cells produced in Meiosis $I$.

(C) The correct statement is that the synaptonemal complex and nuclear envelope completely disappear at the end of diakinesis,not diplotene. In diplotene,the synaptonemal complex dissolves,but the nuclear envelope remains intact until the end of diakinesis.

(A) During the $Leptotene$ stage of $Meiosis-I$,the chromosomes become gradually visible under a light microscope.
In this stage,the chromosomes are often oriented with their ends directed towards the nuclear envelope,a configuration known as the $Bouquet$ stage.
This specific arrangement is a characteristic feature of the $Leptotene$ phase.

(C) The diplotene stage of prophase-$I$ is characterized by the following features:
$1$. Desynapsis: The homologous chromosomes begin to separate from each other except at the sites of crossovers (chiasmata).
$2$. Dictyotene stage: In some vertebrates (like human oocytes),the diplotene stage can last for months or years,which is known as the dictyotene stage.
$3$. Longest phase of prophase-$I$: Diplotene is recognized as the longest sub-stage of prophase-$I$ in many organisms.
Therefore,the correct characteristics are $(a)$,$(c)$,and $(f)$.

(C) The recombination nodules are the sites where crossing over occurs between non-sister chromatids of homologous chromosomes.
These nodules appear on the synaptonemal complex specifically during the $Pachytene$ stage of $Meiosis-I$.
Therefore,the correct stage is the $Pachytene$ stage.

(C) The $Diplotene$ stage of $Prophase-I$ is characterized by the dissolution of the synaptonemal complex and the separation of homologous chromosomes,except at the sites of crossovers called $chiasmata$. In many vertebrate oocytes,the $Diplotene$ stage can last for months or years. During this prolonged phase,the chromosomes decondense to form lampbrush chromosomes and become actively engaged in $RNA$ synthesis.

(B) Prophase $I$ of meiosis is divided into five sub-stages: Leptotene,Zygotene,Pachytene,Diplotene,and Diakinesis.
$1$. During Zygotene,homologous chromosomes pair up,a process known as synapsis.
$2$. When synapsis is complete,the cell enters the Pachytene stage.
$3$. In the Pachytene stage,the bivalent chromosomes clearly appear as tetrads,and crossing over (exchange of genetic material between non-sister chromatids of homologous chromosomes) occurs.
$4$. Therefore,the stage described is Pachytene.

(C) Diakinesis is the final stage of meiotic prophase-$I$.
During this stage,the chromosomes are fully condensed and the meiotic spindle is assembled to prepare the homologous chromosomes for separation.
The most characteristic feature of diakinesis is the complete terminalisation of chiasmata,where the chiasmata move towards the ends of the chromatids.
Additionally,the nucleolus disappears and the nuclear envelope breaks down.
$RNA$ synthesis is also inhibited during this stage as the chromosomes become highly condensed and transcriptionally inactive.

(C) In the oocytes of many vertebrates,the diplotene stage of prophase-$I$ is temporarily arrested for an extended period. This prolonged,suspended diplotene stage is specifically referred to as the $Dictyotene$ stage. During this phase,the chromosomes decondense and become transcriptionally active,allowing for the accumulation of maternal resources required for future embryonic development.

(C) The synaptonemal complex is a protein structure that forms between homologous chromosomes during the pachytene stage of prophase-$I$ of meiosis.
It facilitates the pairing (synapsis) of homologous chromosomes and is essential for crossing over.
Therefore,the Assertion is correct.
However,the synaptonemal complex is specific to meiosis,not mitosis.
Mitosis involves the division of somatic cells where homologous chromosomes do not pair up or form a synaptonemal complex.
Thus,the Reason is incorrect.

(C) In Metaphase $I$ of meiosis,each chromosome of a bivalent attaches to a single spindle fiber from one pole,not two. This is because the kinetochores of sister chromatids are oriented towards the same pole.
Therefore,the Assertion is incorrect.
In Metaphase $I$,the bivalents (homologous pairs) align at the equatorial plate (metaphasic plate). Thus,the Reason is correct.
Hence,the correct option is $C$.

(A) In Meiosis-$I$,the homologous chromosomes separate and move to opposite poles,while the sister chromatids remain attached at the centromere.
Because the homologous pairs separate,the number of chromosomes in each daughter cell is reduced to half compared to the parent cell.
Therefore,Anaphase-$I$ is indeed the phase where the reduction in chromosome number occurs.
The Reason statement correctly describes the movement of homologous chromosomes to opposite poles with their chromatids intact.
Thus,both statements are correct,and the Reason explains why the chromosome number is reduced.

(A) The diplotene stage of prophase-$I$ of meiosis is characterized by the dissolution of the synaptonemal complex.
However,the homologous chromosomes do not separate completely at the sites of crossing over.
These $X$-shaped structures are called chiasmata.
Therefore,the diplotene stage is the stage where chiasmata become visible and can be counted.
Since the reason explains why chiasmata are visible and countable at this stage,both statements are correct and the reason is the correct explanation.

(D) Meiosis is a specialized type of cell division that reduces the chromosome number by half,resulting in the production of haploid daughter cells.
In sexually reproducing organisms,meiosis occurs in specialized cells called meiocytes.
$A$ meiocyte is a diploid $(2n)$ cell that undergoes meiosis to produce haploid $(n)$ gametes.
Conidia and gemmules are structures involved in asexual reproduction,where mitosis occurs.
Megaspores are haploid cells produced after meiosis,not the site where meiosis occurs.

(A) Meiosis is a specialized type of cell division that reduces the chromosome number by half,resulting in the production of haploid cells.
This process is essential during gametogenesis to ensure that gametes (sperm and egg) contain half the number of chromosomes compared to the parent organism.
When fertilization occurs,the fusion of these haploid gametes restores the diploid chromosome number in the zygote.
Therefore,meiotic cell division occurs specifically during gametogenesis.

(D) Non-disjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division.
In a male with $44+XY$ chromosomes,the first meiotic division involves the separation of the $X$ and $Y$ chromosomes.
If non-disjunction occurs during the first meiotic division,the $XY$ pair fails to separate and moves into one daughter cell,while the other daughter cell receives no sex chromosomes.
Consequently,after the second meiotic division,the resulting gametes will have genotypes $22+XY$ and $22+0$ (which is $22$).

(C) Meiosis is a reductional division consisting of two stages: Meiosis-$I$ and Meiosis-$II$.
In Meiosis-$I$,homologous chromosomes separate,but the centromeres remain intact.
In Anaphase-$II$,the centromere of each chromosome splits,allowing the sister chromatids to separate and move toward opposite poles.
Therefore,the splitting of the centromere is a characteristic feature of Anaphase-$II$.

(C) The prophase of meiosis-$I$ is divided into five sub-stages: $Leptotene$, $Zygotene$, $Pachytene$, $Diplotene$, and $Diakinesis$.
$1$. $Leptotene$: Chromosomes become visible as compact threads.
$2$. $Zygotene$: Synapsis occurs between homologous chromosomes.
$3$. $Pachytene$: Crossing over takes place between non-sister chromatids.
$4$. $Diplotene$: The dissolution of the synaptonemal complex occurs, and homologous chromosomes separate except at the sites of crossovers, forming $Chiasmata$.
$5$. $Diakinesis$: This is the final stage of meiotic prophase-$I$. The distinctive feature of this stage is the $terminalisation$ of $chiasmata$. The chromosomes are fully condensed, and the meiotic spindle is assembled to prepare the homologous chromosomes for separation.