Meiosis Questions in English

(N/A) Gametogenesis is the process of formation of male and female gametes.
All gametes are haploid,meaning they possess a single set of chromosomes $(n)$.
These gametes are formed as a result of meiosis,which is a reductional division.
Meiosis reduces the chromosome number to half in the gametes,ensuring that the diploid number $(2n)$ is restored during fertilization.
Therefore,meiosis and gametogenesis are fundamentally interlinked.

(B) During the $pachytene$ stage of $prophase-I$ in meiosis,the phenomenon of crossing over takes place.
Recombination nodules are protein complexes that appear on the synaptonemal complex at the sites where crossing over occurs.
These nodules facilitate the exchange of genetic material between non-sister chromatids of homologous chromosomes.
Therefore,the appearance of recombination nodules characterizes the sites at which crossing over occurs.

(A) Meiosis is a reductional division that occurs in two sequential stages: Meiosis-$I$ and Meiosis-$II$.
$DNA$ replication occurs during the $S$ phase of Interphase,which precedes Meiosis-$I$. There is no $S$ phase or $DNA$ replication in Meiosis-$II$.
Pairing of homologous chromosomes (synapsis) and recombination (crossing over) are characteristic features of Prophase-$I$ of Meiosis-$I$.
At the end of Meiosis-$II$,four haploid daughter cells are produced from a single diploid parent cell.
Therefore,the statement that $DNA$ replication occurs in the $S$ phase of Meiosis-$II$ is incorrect.

(B) 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 involves two successive nuclear divisions,known as meiosis-$I$ and meiosis-$II$.
Starting from a single diploid $(2n)$ cell,the process results in the formation of four haploid $(n)$ daughter cells.

(B) During $Meiosis$, specifically in $Prophase-I$, the process of $crossing-over$ occurs between non-sister chromatids of homologous chromosomes.
This process leads to the exchange of genetic material, resulting in new combinations of genes (recombination).
Therefore, the genetic constitution of the chromosomes is altered in the daughter cells compared to the parent cell.
In contrast, $Mitosis$ is an equational division where the genetic constitution remains identical.

(A) Meiosis-$I$ is a reductional division,and its prophase-$I$ is significantly longer and more complex than the prophase of mitosis or prophase-$II$ of meiosis.
Prophase-$I$ is further subdivided into five distinct stages: Leptotene,Zygotene,Pachytene,Diplotene,and Diakinesis.
These stages involve complex processes such as synapsis,crossing over,and the formation of chiasmata,which require a substantial amount of time to complete.
Therefore,Prophase-$I$ is considered the longest phase of meiosis.

(B) Prophase-$I$ of meiosis is a complex and long 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 (synapsis).
$3$. Pachytene: Crossing over takes place between non-sister chromatids of homologous chromosomes.
$4$. Diplotene: The synaptonemal complex dissolves,and homologous chromosomes start to separate,revealing chiasmata.
$5$. Diakinesis: The final stage where chromosomes are fully condensed and the nucleolus disappears,preparing for metaphase-$I$.
Therefore,the correct sequence is Leptotene $\rightarrow$ Zygotene $\rightarrow$ Pachytene $\rightarrow$ Diplotene $\rightarrow$ Diakinesis.

(B) The process of crossing over occurs during the $Pachytene$ stage of $Prophase-I$ in meiosis.
Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes.
This process is mediated by the enzyme $Recombinase$,which facilitates the breakage and reunion of $DNA$ strands.
Therefore,the enzyme $Recombinase$ is required during the $Pachytene$ stage.

(B) During $Metaphase-I$ of meiosis,homologous chromosomes pair up (synapsis) to form bivalents or tetrads. These pairs align along the metaphase plate (equatorial plate). In contrast,during $Metaphase$ of mitosis and $Metaphase-II$ of meiosis,individual chromosomes (not pairs) align on the metaphase plate.

(B) During the pachytene stage of prophase-$I$ in meiosis,the process of crossing over occurs between non-sister chromatids of homologous chromosomes.
At this stage,the bivalent chromosomes (pairs of homologous chromosomes) clearly appear as tetrads,meaning they consist of four chromatids.
Therefore,the chromosomes are described as $Tetrad$ and $Bivalent$.

(A) During the process of meiosis,specifically in Prophase-$I$,the chromosomes begin to pair up. This pairing process is known as $Synapsis$. This event is the characteristic feature of the $Zygotene$ stage of Prophase-$I$. Therefore,$P$ is $Synapsis$ and $Q$ is $Zygotene$.

(A) During Anaphase-$II$,the centromere of each chromosome splits,and the sister chromatids separate.
Each separated chromatid is now considered an individual chromosome.
$1$. Centromere: Since the centromere splits,each daughter chromosome has $1$ centromere.
$2$. Chromatid: After the split,the structure is referred to as a chromosome,not a chromatid; however,in the context of the separated unit,it represents $1$ chromatid.
$3$. Kinetochore: Each centromere has $2$ kinetochores (one on each side),but since the centromere has split,each daughter chromosome retains $1$ kinetochore facing the pole to which it is being pulled.
Therefore,for each daughter chromosome in Anaphase-$II$,the count is $1$ centromere,$1$ chromatid,and $1$ kinetochore.

(D) 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. In oocytes of some vertebrates,diplotene can last for months or years (dictyotene stage). Statement $D$ is incorrect because homologous chromosomes do not completely separate; they remain attached at the chiasmata.

(A) Crossing over is a biological process that occurs during the $pachytene$ stage of $prophase-I$ of $meiosis$.
It involves the exchange of genetic material between the non-sister chromatids of homologous chromosomes.
This process leads to genetic recombination,which is essential for creating genetic diversity in sexually reproducing organisms.
Therefore,the correct option is $A$.

(B) In image $P$,we can observe homologous chromosomes pairing up to form bivalents or tetrads,which is a characteristic feature of Prophase-$I$ of meiosis.
In image $Q$,the homologous pairs (bivalents) are aligned at the equatorial plate,and spindle fibers are attached to the kinetochores of the homologous chromosomes. This alignment of bivalents at the metaphase plate is a characteristic feature of Metaphase-$I$ of meiosis.
Therefore,the correct stages are Prophase-$I$ and Metaphase-$I$.

(C) The image shows two cells undergoing cell division. In each cell,the sister chromatids are being pulled apart towards opposite poles. This separation of sister chromatids is the characteristic feature of Anaphase-$II$ of meiosis or Anaphase of mitosis. However,since the chromosomes are shown as single chromatids moving towards the poles,it represents Anaphase-$II$ of meiosis. In Anaphase-$I$,homologous chromosomes separate,not sister chromatids. Therefore,the correct stage is Anaphase-$II$.

(A) Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes.
It occurs during the $Pachytene$ stage of $Prophase-I$ of $Meiosis-I$.
During this stage,the bivalent chromosomes become clearly visible as tetrads,and the phenomenon of recombination is mediated by the enzyme recombinase.

(D) Meiosis is a reductional division that reduces the chromosome number by half.
$A$. Meiosis involves crossing over during prophase-$I$,which introduces genetic variation in gametes.
$B$. Meiosis typically occurs in diploid $(2n)$ cells to produce haploid $(n)$ gametes.
$C$. In animals,meiosis is specifically involved in gametogenesis (formation of eggs and sperm).
$D$. This statement is incorrect. While the vegetative body of many algae is haploid $(n)$,they undergo zygotic meiosis after fertilization (fusion of gametes) to restore the haploid state. Therefore,meiosis does occur in the life cycle of algae.

(C) In the given diagram,stage $P$ shows homologous chromosomes aligned at the equatorial plate,which is characteristic of Metaphase-$I$ of meiosis.
Stage $Q$ shows the splitting of centromeres and the movement of sister chromatids towards opposite poles,which is characteristic of Anaphase-$II$ of meiosis.
Therefore,$P$ is Metaphase-$I$ and $Q$ is Anaphase-$II$.

(C) In the oocytes of some vertebrates,the $Diplotene$ stage of $Meiosis-I$ can remain suspended for months or even years.
This prolonged stage is known as the $Dictyotene$ stage.
During this phase,the chromosomes decondense and become transcriptionally active to synthesize materials required for the growth of the oocyte.
Therefore,the correct option is $C$.

(B) During the $pachytene$ stage of $prophase-I$ in meiosis,the phenomenon of crossing over occurs.
Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes.
This process is mediated and catalyzed by an enzyme complex known as $recombinase$.
$Recombinase$ facilitates the breaking and rejoining of $DNA$ strands,ensuring genetic recombination.

(C) Prophase $I$ of meiosis is divided into five sub-stages: Leptotene,Zygotene,Pachytene,Diplotene,and Diakinesis.
$1$. $(b)$ Chromosomes become gradually visible under the microscope occurs during Leptotene.
$2$. $(a)$ Synapsis of homologous chromosomes occurs during Zygotene.
$3$. $(c)$ Crossing over between non-sister chromatids occurs during Pachytene.
$4$. $(e)$ Dissolution of the synaptonemal complex occurs during Diplotene.
$5$. $(d)$ Terminalisation of chiasmata occurs during Diakinesis.
Therefore,the correct sequence is $(b), (a), (c), (e), (d)$.

(A) During the $Zygotene$ stage of $Meiosis-I$,homologous chromosomes pair up,a process known as $Synapsis$.
This pairing is facilitated by the formation of a $Synaptonemal$ $complex$.
The paired homologous chromosomes are called $Bivalents$ or $Tetrads$.
Therefore,the formation of $Bivalents$ or $Tetrads$ is a characteristic feature of the $Zygotene$ stage,associated with the $Synaptonemal$ $complex$.

(D) The splitting of the centromere occurs during the anaphase of mitosis or anaphase $II$ of meiosis.
During Metaphase $I$ and $II$,chromosomes align at the equatorial plate.
During telophase,chromosomes reach their respective poles and decondense.

(C) The process of recombination occurs at the Pachytene stage of prophase $I$.
This stage is characterized by the appearance of recombination nodules,which are sites at which crossing over occurs between non-sister chromatids of homologous chromosomes.

(D) - During the leptotene stage,the chromosomes become gradually visible under the light microscope as they begin to condense.
- The beginning of the diplotene stage is recognized by the dissolution of the synaptonemal complex and the tendency of the recombined homologous chromosomes of the bivalents to separate from each other,except at the sites of crossovers (chiasmata).
- Therefore,both Statement $I$ and Statement $II$ are true.

$(B)$ The correct matching is as follows:
$(A)$ Diakinesis: This is the final stage of meiotic prophase-$I$, characterized by the completion of terminalisation of chiasmata.
$(B)$ Pachytene: This stage is characterized by the appearance of recombination nodules, which are the sites at which crossing over occurs between non-sister chromatids of homologous chromosomes.
$(C)$ Zygotene: During this stage, homologous chromosomes pair up, a process called synapsis, which is accompanied by the formation of a complex structure called the synaptonemal complex.
$(D)$ Leptotene: During this stage, the chromosomes become gradually visible under the light microscope and look like thin threads.
Therefore, the correct sequence is $A-II, B-IV, C-I, D-III$.

(B) In the provided image,$A$ represents Metaphase$-I$ of meiosis,where homologous chromosomes align at the equatorial plate.
$B$ represents Anaphase$-I$ of meiosis,where homologous chromosomes separate and move towards opposite poles,while sister chromatids remain attached at their centromeres.
Therefore,the correct identification is Metaphase$-I$ and Anaphase$-I$.

(C) During the $Pachytene$ stage of $Meiosis-I$,crossing over occurs between the non-sister chromatids of homologous chromosomes. As the cell progresses into the $Diplotene$ stage,the synaptonemal complex dissolves,and the homologous chromosomes begin to separate from each other. However,they remain attached at the sites where crossing over occurred. These $X$-shaped structures are known as $Chiasmata$.

(B) In meiosis-$I$,the homologous chromosomes pair up to form bivalents or tetrads.
During Metaphase-$I$,these bivalent chromosomes align on the equatorial plate (metaphase plate).
This alignment is crucial for the subsequent separation of homologous chromosomes during Anaphase-$I$.
Therefore,the correct phase is Metaphase-$I$.

(D) Homologous chromosomes are a pair of chromosomes,one of which is inherited from the mother and the other from the father. Therefore,the statement that both homologous chromosomes are inherited from the mother is incorrect.

(C) Gametes are reproductive cells that contain half the number of chromosomes compared to somatic cells.
This condition is known as haploidy or monoploidy,represented as $n$.
Hypoploidy,Hyperploidy,and Aneuploidy are abnormal conditions involving the loss or gain of specific chromosomes,which are not characteristic of normal gametes.

(B) The correct matching is as follows:
$A$. Leptotene: During this stage, chromosomes become visible under a light microscope.
$B$. Zygotene: During this stage, homologous chromosomes start pairing together, a process called synapsis.
$C$. Pachytene: During this stage, crossing over occurs, which is the exchange of genetic material between non-sister chromatids of homologous chromosomes.
$D$. Diplotene: During this stage, the synaptonemal complex dissolves, and homologous chromosomes begin to separate except at the sites of crossovers (chiasmata).
$E$. Diakinesis: This is the final stage of prophase $I$, characterized by the terminalisation of chiasmata.
Therefore, the correct sequence is $A-i, B-ii, C-iii, D-iv, E-v$.

(A) The correct answer is $A$ (Pachytene).
$Recombinase$ is an enzyme that facilitates the process of crossing over between non-sister chromatids of homologous chromosomes.
This process occurs specifically during the $Pachytene$ stage of $Prophase \ I$ in $Meiosis \ I$.

(D) The correct answer is $D$.
During the $zygotene$ stage of $prophase-I$ in $meiosis$,homologous chromosomes pair up in a process known as $synapsis$.
This pair of synapsed homologous chromosomes is referred to as a $bivalent$ or a $tetrad$ (because it consists of four chromatids).

(B) The correct answer is $B$.
Crossing over is a process that occurs during the pachytene stage of prophase $I$ of meiosis.
It involves the exchange of genetic material between non-sister chromatids of homologous chromosomes.
The enzyme complex responsible for catalyzing this recombination event is known as recombinase.

(A) is the correct sequence: Synapsis $\rightarrow$ Crossing over $\rightarrow$ Chiasmata $\rightarrow$ Terminalisation.
Prophase $I$ of meiosis is divided into $5$ sub-stages: leptotene,zygotene,pachytene,diplotene,and diakinesis.
$1$. Synapsis: Pairing of homologous chromosomes occurs during the zygotene stage.
$2$. Crossing over: Exchange of genetic material between non-sister chromatids of homologous chromosomes occurs during the pachytene stage.
$3$. Chiasmata: The $X$-shaped structures formed at the sites of crossing over become visible during the diplotene stage.
$4$. Terminalisation: The shifting of chiasmata towards the ends of the chromosomes occurs during the diakinesis stage.

(D) The correct answer is $D$.
Crossing over is the process of exchange of genetic material between non-sister chromatids of homologous chromosomes.
This process occurs during the pachytene stage of prophase-$I$ of meiosis.
It is an enzyme-mediated process,and the enzyme involved in this process is known as recombinase.

(B) The correct answer is $B$.
During the pachytene stage of prophase-$I$ of meiosis,the process of crossing over occurs.
Crossing over involves the exchange of genetic material between non-sister chromatids of homologous chromosomes.
This process is mediated by the enzyme 'recombinase',which facilitates the breakage and reunion of $DNA$ strands.

(A) The correct answer is $A$.
During the prophase $I$ of meiosis,homologous chromosomes pair up to form a structure known as a bivalent or tetrad.
Each homologous chromosome consists of two sister chromatids joined by a single centromere.
Since a bivalent consists of two homologous chromosomes,it contains a total of $4$ chromatids ($2$ from each chromosome) and $2$ centromeres ($1$ from each chromosome).

(C) The correct answer is $C$.
Crossing over is the process of exchange of genetic material between non-sister chromatids of homologous chromosomes during the $pachytene$ stage of $prophase-I$ of $meiosis$.
The visible manifestation or expression of this crossing over,which can be observed under a microscope during the $diplotene$ stage,is known as $chiasmata$ (singular: $chiasma$).
These $X$-shaped structures represent the sites where the physical exchange of $DNA$ segments has occurred.