Meiosis Questions in English

(C) During the $pachytene$ stage of $prophase-I$ of $meiosis$,homologous chromosomes pair up to form a structure known as a $bivalent$ or $tetrad$.
Each $bivalent$ consists of two homologous chromosomes,and since each chromosome has already replicated to form two sister chromatids,the structure contains a total of four chromatids.
Therefore,a $tetrad$ is composed of two sets of homologous chromosomes,where each chromosome consists of two chromatids.

(D) The term "meiosis" was coined by $J.B. Farmer$ and $J.E.S. Moore$ in $1905$.
They derived the term from the Greek word 'meio' meaning 'to lessen' or 'to diminish', describing the reductional division process where the chromosome number is halved.

(A) Condensation of chromosomes is a characteristic feature of the prophase stage of cell division.
In meiosis,the condensation of chromatin material into distinct chromosomes begins during prophase-$I$.
This process allows the chromosomes to become visible under a microscope and facilitates the pairing of homologous chromosomes (synapsis) and crossing over.

(C) The stage that serves as the connecting link between Meiosis $I$ and Meiosis $II$ is known as Interkinesis.
Interkinesis is a short-lived resting phase that occurs after the completion of Meiosis $I$ and before the onset of Meiosis $II$.
During this stage,there is no replication of $DNA$,although the cell may undergo some growth and protein synthesis.
Therefore,the correct option is $C$.

(D) Synapsis is the pairing of homologous chromosomes during the $zygotene$ sub-stage of $prophase-I$ in meiosis. This process involves the formation of a synaptonemal complex,which facilitates the alignment and pairing of homologous chromosomes. This stage is characterized by a small amount of $DNA$ replication,often referred to as $zygotene$ $DNA$.

(D) . Diakinesis is the final stage of prophase-$I$ in meiosis.
Since meiosis occurs in reproductive cells,young flower buds are the most suitable material for observing meiotic stages like diakinesis because they contain developing anthers where microsporogenesis takes place.

(A) The synaptonemal complex is a protein structure that forms between homologous chromosomes during the $Zygotene$ stage of $Prophase-I$ of $Meiosis$.
It facilitates the process of synapsis,which is the pairing of homologous chromosomes.
Therefore,the correct answer is $Meiosis$.

(A) The synaptonemal complex is a protein structure that forms between homologous chromosomes during meiotic prophase-$I$.
It was first discovered and described by Montrose $J$. Moses in $1956$.

(B) Recombinant nodules are protein complexes that appear at the sites of crossing over during the pachytene stage of prophase-$I$ of meiosis. These nodules facilitate the exchange of genetic material between non-sister chromatids of homologous chromosomes. Since the pachytene stage is a sub-stage of prophase-$I$,the correct answer is prophase.

(B) During meiosis,the process of crossing over occurs during Prophase-$I$,which leads to genetic recombination.
Additionally,the independent assortment of homologous chromosomes during Metaphase-$I$ ensures that the resulting daughter cells contain a unique combination of genetic material.
Therefore,the four daughter cells produced at the end of meiosis are genetically different from each other and from the parent cell.

(A) Bivalents are formed during the $Zygotene$ stage of $Meiosis-I$ when homologous chromosomes pair up (synapsis).
Each bivalent consists of two homologous chromosomes,which together contain four chromatids.
Because of these four chromatids,the bivalent is also referred to as a $Tetrad$.

(D) The correct answer is $D$.
In meiosis-$I$,the process of crossing over occurs during the pachytene stage.
Following pachytene,the homologous chromosomes begin to separate from each other due to the dissolution of the synaptonemal complex,a process known as repulsion.
This stage is called diplotene.

(D) During the pachytene stage of meiosis,the homologous chromosomes undergo crossing over.
Each bivalent consists of two homologous chromosomes,and since each chromosome consists of two sister chromatids,the bivalent appears as a four-stranded structure,known as a tetrad.

(B) During cell division,the contraction of spindle fibres occurs during the Anaphase stage of both mitosis and meiosis ($Anaphase \ I$ and $Anaphase \ II$).
This contraction pulls the sister chromatids (in $Anaphase \ II$) or homologous chromosomes (in $Anaphase \ I$) towards the opposite poles of the cell.
Among the given options,$Anaphase \ II$ is the stage where spindle fibre contraction leads to the separation of sister chromatids.

(B) The process of genetic recombination occurs through crossing over between non-sister chromatids of homologous chromosomes.
This event takes place specifically during the Pachytene sub-stage of Prophase $I$ in meiosis.
Therefore,the correct phase for gene recombination is Prophase $I$.

(A) Meiosis consists of two successive nuclear divisions: Meiosis-$I$ and Meiosis-$II$.
Meiosis-$I$ is known as the reductional division because the chromosome number is reduced to half.
Meiosis-$II$ is known as the equational division because the number of chromosomes remains the same as in the parent cell (similar to mitosis),as it involves the separation of sister chromatids.

(D) 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. The complex formed by a pair of synapsed homologous chromosomes is called a $bivalent$ or a $tetrad$.

(C) In meiosis,the cell starts with a diploid number of chromosomes. During prophase $I$,there are $4$ chromosomes.
After meiosis $I$,the chromosome number is halved,resulting in $2$ chromosomes in each daughter cell.
During anaphase $II$,the sister chromatids separate. Although the number of chromatids doubles temporarily,the number of chromosomes in the cell remains the same as it was at the end of meiosis $I$.
Therefore,at the end of anaphase $II$,each cell still contains $2$ chromosomes.

(A) Meiosis is a reductional division where the chromosome number is halved in the daughter cells compared to the mother cell.
If the daughter cells have $n = 4$ chromosomes,then the mother cell (which is diploid,$2n$) must have had $2 \times 4 = 8$ chromosomes.
Therefore,the mother cell contained $8$ chromosomes.

(D) Meiosis-$II$ is an equational division,similar to mitosis. During Anaphase-$II$,the centromere of each chromosome splits,allowing the sister chromatids to separate and move toward opposite poles of the cell.

(D) During the $Pachytene$ stage of $Meiosis-I$,the process of crossing over occurs between non-sister chromatids of homologous chromosomes.
At this stage,the bivalent (or tetrad) consists of four chromatids and two centromeres.
$A$ bivalent is a pair of homologous chromosomes,where each chromosome consists of two sister chromatids,totaling four chromatids.

(B) In meiosis-$I$,homologous chromosomes pair up to form bivalents (or tetrads).
For a plant with a diploid number $2n = 50$,the number of chromosomes is $50$.
These $50$ chromosomes form $25$ bivalents during prophase-$I$.
At the equatorial plate during metaphase-$I$,these $25$ bivalents align.
Each bivalent acts as a single group or unit at the equatorial plate.
Therefore,the number of chromosome groups at the equatorial plate is $25$.

(A) In $Meiosis-I$,the homologous chromosomes pair up during Prophase $I$ (synapsis) and align at the equatorial plate during Metaphase $I$.
During Anaphase $I$,the homologous chromosomes separate,while the sister chromatids remain associated at their centromeres.
Option $A$ correctly describes this event.
Option $B$ is incorrect because pairing (synapsis) occurs in Prophase $I$,not Metaphase $I$.
Option $C$ is incorrect because Interphase is the preparatory phase for division,not the stage where nuclear envelopes enclose haploid sets (this occurs in Telophase $II$).
Option $D$ is incorrect because Prophase $I$ involves crossing over and synapsis,not the separation of non-homologous chromosomes.

(C) $1$. Prophase $I$: During the pachytene stage of Prophase $I$,crossing over occurs between non-sister chromatids of homologous chromosomes.
$2$. Metaphase $I$: During Metaphase $I$,homologous chromosome pairs (bivalents) align at the equatorial plate. The statement 'Sister chromatids migrate to opposite poles' is incorrect for Metaphase $I$; this occurs in Anaphase $II$.
$3$. Anaphase $I$: During Anaphase $I$,homologous chromosomes separate and move to opposite poles,while sister chromatids remain attached at their centromeres. The statement 'Homologous line up at equator in pairs' is incorrect for Anaphase $I$; this occurs in Metaphase $I$.
Therefore,only statement $1$ is correct,while $2$ and $3$ are false.

(B) Meiosis-$I$ is a reductional division where the homologous chromosomes separate,while the sister chromatids remain associated at their centromeres.
During $Anaphase-I$,the homologous chromosomes move to opposite poles of the cell.
As a result,each pole receives only half the number of chromosomes compared to the parent cell,effectively halving the chromosome number.

(D) Terminalization refers to the shifting of chiasmata towards the ends of the chromosomes. This process occurs during the $Diakinesis$ stage,which is the final stage of $Prophase-I$ of meiosis. During this phase,the chromosomes are fully condensed,and the nucleolus disappears.

(A) Meiosis occurs in two stages: meiosis $I$ and meiosis $II$.
During meiosis $I$,homologous chromosomes separate,and the number of chromosomes in the daughter cells is reduced to half.
This division is known as reductional division.
During meiosis $II$,the centromere splits,and the chromosome number remains the same in the daughter cells; therefore,meiosis $II$ is known as equational division.
If the number of chromosomes in a cell after meiosis $I$ is $48$,then after the completion of meiosis $II$,the daughter cells will also have $48$ chromosomes because meiosis $II$ is an equational division.

(B) In mitosis,prophase involves the condensation of chromatin into chromosomes,but no pairing of homologous chromosomes occurs.
In contrast,prophase-$I$ of meiosis is characterized by specific events such as synapsis (pairing of homologous chromosomes) and the formation of bivalents or tetrads (a group of four chromatids).
Therefore,the formation of tetrads is a unique feature of prophase-$I$ of meiosis that is absent in the prophase of mitosis.

(A) During the $Meiosis-I$ prophase,the $Diplotene$ stage is characterized by the dissolution of the synaptonemal complex. The homologous chromosomes of the bivalents start to separate from each other except at the sites of crossovers. These $X$-shaped structures are called $Chiasmata$. Therefore,the formation and visibility of chiasmata occur during the $Diplotene$ stage.

(B) In $Meiosis-I$,specifically during $Metaphase-I$,the homologous chromosomes align at the equatorial plate as bivalents (tetrads).
Unlike $Mitosis$ or $Meiosis-II$,the centromeres of the chromosomes do not divide during $Metaphase-I$.
The centromeres remain intact,and the sister chromatids stay attached to each other throughout $Anaphase-I$ as the homologous chromosomes move toward opposite poles.

(C) During meiosis $Prophase-I$,the process begins with the $Leptotene$ stage,where chromosomes appear as thin,thread-like structures.
In the subsequent stage,known as $Zygotene$,homologous chromosomes undergo pairing,a process called $Synapsis$.
This pairing is facilitated by the formation of a $Synaptonemal$ complex.
Therefore,the correct stage for the pairing of homologous chromosomes is $Zygotene$.

(B) The process of pairing of homologous chromosomes is known as synapsis.
This process occurs during the $Zygotene$ stage of $Prophase-I$ of meiosis.
During this stage,homologous chromosomes align side-by-side to form bivalents or tetrads.

(D) Meiosis is a specialized type of cell division that reduces the chromosome number by half,resulting in the production of haploid daughter cells.
This process occurs in germ cells to produce gametes (sex cells).
During meiosis,the diploid $(2n)$ parent cell undergoes two successive nuclear and cytoplasmic divisions,resulting in four haploid $(n)$ daughter cells.
This ensures that the chromosome number remains constant across generations after fertilization.

(B) Meiosis was first described in sea urchin eggs by the German biologist Oscar Hertwig in $1876$. It was later described again in $1883$ at the level of chromosomes by the Belgian zoologist Edouard Van Beneden in Ascaris eggs. However,the term 'meiosis' was coined by $J$.$B$. Farmer and $J$.$E$.$S$. Moore in $1905$. Among the given options,Oscar Hertwig is the primary discoverer,but in many historical contexts,the process of meiosis in plants was studied by Wilhelm Hofmeister. Given the standard options provided in many competitive exams,$B$ (Hofmeister) is often cited in the context of early plant meiosis studies.

(D) Prophase $I$ of meiosis is a complex and prolonged phase compared to the prophase of mitosis. It is subdivided into five distinct stages based on chromosomal behavior:
$1$. Leptotene: Chromosomes become visible as compact threads.
$2$. Zygotene: Pairing of homologous chromosomes occurs,known as synapsis.
$3$. Pachytene: Crossing over takes place between non-sister chromatids of homologous chromosomes.
$4$. Diplotene: The synaptonemal complex dissolves,and homologous chromosomes begin to separate,revealing chiasmata.
$5$. Diakinesis: The final stage where chromosomes are fully condensed and the nucleolus disappears.
Therefore,the correct chronological sequence is Leptotene — zygotene — pachytene — diplotene — diakinesis.

(C) In a species with $2n = 16$,the number of chromosomes is $16$.
During $Prophase-I$ of meiosis,homologous chromosomes pair up to form bivalents or tetrads.
The number of tetrads formed is equal to $n$,where $n$ is the haploid number of chromosomes.
Since $2n = 16$,$n = 8$. Thus,$8$ tetrads are formed during $Prophase-I$.
During $Prophase-II$,the cell is haploid $(n = 8)$. Each chromosome consists of two sister chromatids,which are referred to as diads.
Therefore,$8$ diads are formed during $Prophase-II$.

(A) Pachytene is the $3^{rd}$ stage of prophase-$I$ of meiosis. During this stage,the bivalent chromosomes become clearly visible as tetrads,and the phenomenon of crossing over occurs between non-sister chromatids of homologous chromosomes.

(C) During the $Diplotene$ stage of $Prophase-I$ in meiosis,the homologous chromosomes begin to separate,but they remain attached at specific points called $Chiasmata$.
As the cell progresses into the $Diakinesis$ stage,these $Chiasmata$ move towards the ends of the chromosomes,a process known as $Terminalization$.
This movement is driven by the repulsion between homologous chromosomes,which is primarily attributed to $Electrostatic$ forces between the chromatids.
Therefore,the force responsible for the terminalization of chiasmata is $Electrostatic$ in nature.

(B) Prophase of $Meiosis-I$ is significantly longer and more complex than the prophase of $Mitosis$.
This is because $Meiosis-I$ prophase is divided into five distinct sub-stages: $Leptotene$,$Zygotene$,$Pachytene$,$Diplotene$,and $Diakinesis$.
These stages involve complex processes such as synapsis,crossing over,and the formation of chiasmata,which are not present in mitotic prophase.

(B) Meiosis is a specialized type of cell division that reduces the chromosome number by half,resulting in the production of four haploid daughter cells.
It involves two successive nuclear and cytoplasmic divisions,known as Meiosis-$I$ and Meiosis-$II$.
Therefore,in one meiotic cell division,the cell divides twice.

(B) is the correct answer. Meiosis is characterized by the process of crossing over,which occurs during the pachytene stage of prophase-$I$.
Crossing over involves the exchange of genetic material between non-sister chromatids of homologous chromosomes,leading to genetic variation.
Meiosis is a reductional division where a diploid $(2n)$ cell divides to form four haploid $(n)$ daughter cells,whereas mitosis is an equational division where the chromosome number remains unchanged.

(D) During meiosis,the centromeres do not divide in Meiosis $-I$.
In $Anaphase-II$,the centromeres of each chromosome split,allowing the sister chromatids to separate.
These separated chromatids then move toward opposite poles and are referred to as individual chromosomes.
This process is similar to the mitotic division of centromeres.

(C) Meiosis $I$ is known as the reductional division. During this phase,the homologous chromosomes separate,and the number of chromosomes in each daughter cell is reduced to half of the original number present in the parent cell. Meiosis $II$ is similar to mitosis,where the chromosome number remains the same.

(C) Meiosis is a type of cell division that reduces the chromosome number by half,resulting in the production of haploid gametes.
In flowering plants,meiosis occurs in the microspore mother cells $(PMC)$ located within the anthers to produce microspores (pollen grains).
Root tips and cambium undergo mitosis for growth and development.
Pollen grains are the products of meiosis and do not undergo meiosis themselves.

(A) During the $Zygotene$ stage of $Prophase-I$ of $Meiosis$,homologous chromosomes begin to pair up. This process of association is called $Synapsis$. The paired chromosomes are known as $Bivalents$ or $Tetrads$.

(C) The diploid number of chromosomes $(2n)$ is $8$.
During meiosis-$I$,the homologous chromosomes separate,reducing the chromosome number to half $(n = 4)$.
However,each chromosome still consists of two sister chromatids held together at the centromere.
Therefore,the number of chromatids in each daughter cell at the end of meiosis-$I$ is $4 \times 2 = 8$.

(C) During the $diplotene$ stage of $Meiosis-I$,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 $chiasmata$. Thus,the homologous chromosomes remain united by $chiasmata$ during this stage.

(C) During the $Prophase-I$ of meiosis,homologous chromosomes pair up to form bivalents or tetrads.
Crossing over occurs between non-sister chromatids of homologous chromosomes at specific points.
These $X$-shaped structures,where the exchange of genetic material has occurred,are known as $Chiasmata$.
$Chiasmata$ are clearly visible during the $Diplotene$ stage of $Prophase-I$.

(A) Leptotene is the first stage of prophase $I$ of meiosis. During this stage,the chromosomes become gradually visible under a light microscope. The chromosomes appear as thin,long,thread-like structures.

(C) During the pachytene stage of prophase-$I$ of meiosis,the exchange of genetic material occurs between non-sister chromatids of homologous chromosomes.
This process is known as crossing over.
It leads to genetic recombination,which is essential for genetic diversity in sexually reproducing organisms.