Gametogenesis Questions in English

(C) Spermiogenesis is the process of transformation of a non-motile spermatid into a mature,motile spermatozoon (sperm).
In oogenesis,the ootid (the product of meiosis) does not undergo any such morphological transformation to become an ovum.
Therefore,spermiogenesis is a unique phase in spermatogenesis that has no equivalent process in oogenesis.

(D) Oogenesis is the process of formation,development,and maturation of haploid ova from diploid germinal cells of the ovary.
Oogenesis comprises three phases:
$(i)$ Multiplication phase: Where oogonia multiply by mitosis.
$(ii)$ Growth phase: Where oogonia grow in size to form primary oocytes.
$(iii)$ Maturation phase: Where primary oocytes undergo meiotic divisions to form haploid ova.

(A) The process of formation of haploid ova from diploid germinal cells $(2n)$ of the ovary is called oogenesis.
$A$. Oogenesis: The production of female gametes (ova).
$B$. Ovulation: The release of a secondary oocyte from the ovary.
$C$. Oviposition: The act of laying eggs.
$D$. Oviparity: $A$ reproductive strategy where animals lay eggs that develop outside the mother's body.

(B) During oogenesis,one secondary oocyte undergoes meiosis-$II$ to produce one functional ovum and one polar body. Therefore,$100$ secondary oocytes will produce $100$ ova.
During spermatogenesis,one secondary spermatocyte undergoes meiosis-$II$ to produce two spermatids,which then differentiate into two spermatozoa (sperms). Therefore,$100$ secondary spermatocytes will produce $100 \times 2 = 200$ sperms.
Thus,the correct answer is $100$ ova and $200$ sperms.

(A) $Spermatogenesis$ is the process of formation of haploid functional spermatozoa from diploid germinal cells of the seminiferous tubules.
This process occurs in the testes of males and involves the transformation of spermatogonia into mature sperm cells.

(A) After ejaculation,human sperms travel through the female reproductive tract to reach the ampulla of the fallopian tube for fertilization.
Experimental observations and physiological studies indicate that the average speed of sperm movement within the female reproductive tract is approximately $2$ to $4$ mm/minute.
This motility is essential for the sperm to navigate the cervical mucus and the uterine environment to reach the site of fertilization.

(D) During the maturation phase of oogenesis,the primary oocyte undergoes meiosis $I$ to produce two haploid cells $(n)$.
The larger cell is the secondary oocyte,and the smaller cell is the first polar body.
Subsequently,the secondary oocyte undergoes meiosis $II$,resulting in the formation of a functional egg (ovum) and a second polar body.
These small,non-functional cells that separate from the developing egg are known as polar bodies.

(A) The sperm releases enzymes from the acrosome during the acrosomal reaction,which are collectively known as sperm lysins.
In mammals,the primary enzyme involved in digesting the hyaluronic acid of the corona radiata is $Hyaluronidase$.
This enzyme facilitates the penetration of the sperm through the layers surrounding the ovum.

(B) In humans,the secondary oocyte is arrested at the metaphase-$II$ stage of meiosis-$II$. The entry of the sperm into the secondary oocyte triggers the completion of the second maturation division (meiosis-$II$). This results in the formation of a haploid ovum (ootid) and a second polar body. Subsequently,the fusion of the sperm nucleus and the egg nucleus leads to the formation of a diploid zygote. While the formation of the zygote is the ultimate result,the specific event triggered by the entry of the sperm is the completion of the second maturation division.

(D) The acrosome is a cap-like structure present at the anterior end of the sperm head. It contains hydrolytic enzymes,such as hyaluronidase and acrosin,which are collectively known as sperm lysins. These enzymes are essential for dissolving the protective layers of the ovum (zona pellucida and corona radiata) during the process of fertilization. Therefore,a sperm lacking an acrosome will be unable to penetrate the ovum.

(D) The egg cell (ovum) plays multiple critical roles in reproduction:
$1$. It contributes a haploid set of chromosomes $(n)$ to the zygote,ensuring the diploid number $(2n)$ is restored upon fertilization.
$2$. It provides the majority of the cytoplasm,including organelles like mitochondria,to the developing embryo,as the sperm contributes very little cytoplasm.
$3$. It contains stored nutrients (yolk or cytoplasmic inclusions) that serve as initial food reserves for the early stages of embryonic development.
Therefore,all the given statements are correct.

(B) The correct answer is $(B)$.
In vertebrates,the size of the egg varies significantly,starting from as small as $0.07 \ mm$.
The size of the egg is primarily determined by the amount of yolk reserves present within it.
Animals that require more energy for embryonic development,such as sharks,rays,reptiles,and birds,typically lay eggs with larger dimensions due to a higher yolk content.
In contrast,the eggs of mammals are generally minute and contain very little yolk.

(B) The substances secreted by the sperm that facilitate fertilization are known as Androgamones.
These substances help in the activation of sperm and the penetration of the egg.
In contrast,substances secreted by the egg are known as Gynogamones.
Therefore,the correct option is $B$.

(C) Primordial germ cells $(PGCs)$ are the precursors of gametes. In human embryos,these cells first appear in the wall of the yolk sac,specifically near the allantois,during the early stages of development. From there,they migrate through the dorsal mesentery of the hindgut to reach the developing gonadal ridges,where they eventually differentiate into spermatogonia or oogonia. Among the given options,the allantois is the correct site associated with their early appearance.

(D) During the process of spermiogenesis,the spermatid undergoes significant morphological changes to transform into a functional spermatozoan.
$1$. The nucleus shrinks significantly due to the loss of water from the nuclear sap,which reduces the overall weight of the sperm head.
$2$. The chromatin material becomes highly condensed,and chromosomes are closely packed to facilitate efficient transport.
$3$. Most of the $RNA$ and non-essential nuclear components are removed to minimize the mass of the nucleus.
These adaptations collectively enhance the motility of the spermatozoan,allowing it to swim efficiently toward the ovum.

(A) The tail is the longest,tapering,and vibratile part of the sperm. It facilitates the motility of the sperm,allowing it to swim through the female reproductive tract to reach the ovum. Therefore,the movement of the sperm is primarily performed by the tail.

(D) The human female is homogametic,meaning she produces gametes with the sex chromosome constitution $22 + X$. When an egg is released from the ovary,it is a haploid cell containing $22$ autosomes and one $X$ chromosome. Therefore,the correct option is $(d)$.

(C) In a $Telolecithal$ egg,the yolk is concentrated towards the vegetal pole. The nucleus and the major part of the cytoplasm are displaced towards the animal pole. This type of distribution is observed in the eggs of many vertebrates,such as birds and reptiles,where the yolk content is significant.

(A) Mammalian eggs are classified as alecithal.
Alecithal eggs are those that contain either no yolk or a negligible amount of yolk.
In eutherian mammals,the embryo receives nourishment directly from the mother through the placenta,hence the egg does not require a significant amount of yolk for development.

(B) Human eggs are considered $Alecithal$ because they contain a negligible or extremely small amount of yolk.
Although they are technically $Microlecithal$ (containing very little yolk),in the context of comparative embryology,they are most accurately described as $Alecithal$ due to the near-absence of yolk.

(C) Tertiary egg membranes are typically absent in most mammals. However,they are present in $Prototherians$ (monotremes). These membranes are secreted by the oviduct or accessory female reproductive organs after fertilization,similar to the shell formation in birds and reptiles.

(C) The tertiary egg membrane is secreted by the oviduct as the egg passes through it. Examples include the albumen,shell membranes,and the outermost calcareous shell found in reptiles and birds. Therefore,among the given options,albumen is the correct example of a tertiary egg membrane.

(C) In telolecithal eggs,the yolk is concentrated towards the vegetal pole.
Because of the heavy concentration of yolk at one end,the nucleus and the major part of the cytoplasm are displaced towards the opposite pole,known as the animal pole.
This type of egg is commonly found in vertebrates such as birds and reptiles,where the yolk is abundant (macrolecithal) and distributed unevenly.

(C) The egg of a bird is macrolecithal (large amount of yolk) and telolecithal (yolk concentrated at one pole).
Due to the presence of a massive amount of yolk,the cleavage furrow cannot penetrate the entire egg.
Therefore,the cleavage is restricted to a small disc-like area of the cytoplasm at the animal pole,which is known as discoidal meroblastic cleavage.
This type of cleavage is characteristic of reptiles,birds,and monotreme mammals.

(B) . Meroblastic cleavage is also known as partial or incomplete cleavage,which occurs in macrolecithal and telolecithal eggs.
The cleavage furrow divides only the small amount of active cytoplasm at the animal pole,while the majority of the yolky portion at the vegetal pole or the central area of the egg remains undivided.

(D) Microlecithal eggs are those that contain a very small or negligible amount of yolk.
In $Eutheria$ (placental mammals),the eggs are alecithal or microlecithal because the developing embryo receives nutrition directly from the mother through the placenta.
In contrast,$Reptilia$,$Aves$,and many $Amphibia$ produce macrolecithal or mesolecithal eggs,which contain a large amount of yolk to support the developing embryo outside the mother's body.

(A) The gonads (testes and ovaries) are derived from the embryonic mesoderm. Specifically,they develop from the genital ridges,which are thickenings of the intermediate mesoderm located along the dorsal body wall of the embryo.

(C) The first meiotic division in spermatogenesis is a reductional division.
The $2n$ primary spermatocyte undergoes meiosis-$I$ to produce two haploid $(n)$ daughter cells,which are known as secondary spermatocytes.
Therefore,at the end of the first meiotic division,the cells formed are secondary spermatocytes.

(C) During the development of the oocyte within the ovarian follicle,the plasma membrane of the oocyte and the surrounding follicle cells (granulosa cells) establish direct physical contact. These connections are formed by cytoplasmic processes (also known as microvilli or filopodia) that extend from the oocyte and the follicle cells,allowing for intercellular communication and the transport of nutrients and signaling molecules via gap junctions.

(C) The vitelline membrane is a transparent,non-cellular layer surrounding the plasma membrane (oolemma) of the ovum.
Its thickness is approximately $50 \mathring{A}$.
Therefore,the correct option is $C$.

(D) $Sertoli$ cells are specialized somatic cells located within the seminiferous tubules of the mammalian testes.
They provide structural and nutritional support to the developing germ cells (spermatids) during the process of spermatogenesis.
Leydig cells and interstitial cells are synonymous and are responsible for the secretion of androgens (testosterone),not for the nourishment of sperm.
Oxyntic cells are found in the stomach lining and secrete hydrochloric acid.

(B) The cumulus oophorus (or cumulus ovaricus) is a cluster of follicular cells (membrana granulosa cells) that surrounds the oocyte (ovum) in the Graafian follicle. Therefore,the cumulus covers the ovum.

(A) In human females,ovulation typically occurs once every menstrual cycle (approximately every $28$ days).
This process involves the release of a secondary oocyte from the Graafian follicle.
While it is a common biological observation that ovulation occurs alternately from the two ovaries in successive menstrual cycles,this is not a strictly regulated physiological rule,as one ovary may ovulate more frequently than the other.
However,in the context of standard biological curriculum,the phenomenon is described as occurring alternately from the two ovaries.

(B) In human females,the primary oocytes are formed during fetal development and remain arrested in the prophase-$I$ of meiosis-$I$ within the primary follicles.
As the follicle matures,the primary oocyte completes its first meiotic division just prior to ovulation,resulting in the formation of a large haploid secondary oocyte and a tiny first polar body.
This process occurs while the oocyte is still contained within the Graafian follicle in the ovary.

(D) Holoblastic cleavage refers to the complete division of the egg.
It occurs in eggs with low to moderate amounts of yolk.
$1$. Oligolecithal eggs (e.g.,Amphioxus,mammals) contain very little yolk,resulting in equal holoblastic cleavage.
$2$. Mesolecithal eggs (e.g.,amphibians) contain a moderate amount of yolk,resulting in unequal holoblastic cleavage.
Therefore,holoblastic cleavage occurs in both oligolecithal and mesolecithal eggs.

(B) In mesolecithal eggs,which contain a moderate amount of yolk,cleavage is unequal holoblastic.
This process results in the formation of blastomeres of different sizes: smaller cells known as micromeres and larger cells known as macromeres.

(B) Cortical granules are specialized secretory vesicles located just beneath the plasma membrane (plasmalemma) of the mature oocyte. During the process of fertilization,these granules undergo exocytosis,releasing their contents into the perivitelline space to modify the zona pellucida,thereby preventing polyspermy. Therefore,they are situated on the inner side of the plasmalemma.

(A) The pattern of cleavage is primarily controlled by maternal factors (mRNA and proteins) stored in the egg cytoplasm during oogenesis.
Option $A$ suggests that cleavage requires ongoing protein synthesis. If cleavage is prevented by protein synthesis inhibitors,it implies that the process relies on the translation of maternal mRNA already present in the cytoplasm,which supports the maternal control hypothesis.
Option $B$ shows that $RNA$ synthesis (transcription) is not required for cleavage,confirming that the zygotic genome is not yet active,thus supporting maternal control.
Option $C$ indicates that even with a hybrid genome,early development proceeds normally,suggesting that the initial developmental program is dictated by the egg's cytoplasm.
Option $D$ describes a phenomenon known as maternal effect,where the phenotype is determined by the mother's genotype rather than the zygote's own genes.
However,option $A$ is the least direct evidence because protein synthesis inhibitors can affect general cellular machinery,and some cleavage processes might require specific proteins to be synthesized from maternal templates,making it a less specific indicator of cytoplasmic control compared to the other options.

(D) In the process of oogenesis,one primary oocyte undergoes meiosis $I$ to form one secondary oocyte and one first polar body.
Subsequently,the secondary oocyte undergoes meiosis $II$ to form one mature ovum (egg) and one second polar body.
Therefore,one primary oocyte produces exactly one functional ovum.
Since $1$ primary oocyte produces $1$ ovum,$100$ primary oocytes will produce $100$ ova.

(C) The haploid condition $(n)$ refers to the presence of a single set of chromosomes. In sexually reproducing organisms,gametes such as the ovum (egg cell) and sperm are haploid. Amoeba and bacteria are typically diploid or have complex genomic structures,and the zygote is formed by the fusion of two haploid gametes,making it diploid $(2n)$.

(B) human sperm is a haploid cell $(n)$.
In humans,the diploid number of chromosomes is $46$ $(2n = 46)$,which consists of $44$ autosomes and $2$ sex chromosomes ($XX$ or $XY$).
During meiosis,the chromosome number is halved.
Therefore,a human sperm contains $22$ autosomes and $1$ sex chromosome (either $X$ or $Y$).

(D) An unfertilized human egg is a haploid cell $(n)$.
In humans,the diploid number of chromosomes is $46$ ($44$ autosomes + $XX$ or $XY$).
During meiosis,the chromosome number is halved.
Therefore,an unfertilized egg contains $22$ autosomes and one $X$ chromosome $(22 + X)$.

(A) In humans,the diploid number of chromosomes in a somatic cell is $46$ ($44$ autosomes + $2$ sex chromosomes).
During oogenesis,meiosis occurs,which reduces the chromosome number by half.
Therefore,an unfertilized egg (female gamete) contains $23$ chromosomes in total.
These $23$ chromosomes consist of $22$ autosomes and $1$ sex chromosome ($X$ chromosome).
Thus,the correct composition is $22$ autosomes and $1$ sex chromosome.

(D) In humans, the diploid number of chromosomes is $46$ ($23$ pairs).
These consist of $22$ pairs of autosomes and $1$ pair of sex chromosomes ($XX$ in females and $XY$ in males).
During spermatogenesis, meiosis occurs, resulting in the formation of haploid sperms.
Each sperm receives $22$ autosomes and one sex chromosome.
Since the male genotype is $XY$, $50\%$ of the sperms will contain $22$ autosomes and an $X$ chromosome, while the other $50\%$ will contain $22$ autosomes and a $Y$ chromosome.
Therefore, a sperm contains either an $X$ or a $Y$ chromosome.

(A) The germinal epithelium is the layer of cells that lines the gonads (testes and ovaries).
In the ovaries,it consists of a single layer of cuboidal epithelial cells.
These cells are responsible for the production of gametes through the process of gametogenesis.
Therefore,the correct answer is cuboidal epithelium.

(D) At puberty,the female reproductive system undergoes significant changes. The ovaries begin to mature and release eggs (ova) periodically. This process is known as ovulation. Therefore,the production of the ovum (egg) begins in females at puberty.

(D) Homolecithal or isolecithal eggs are those in which the yolk is very small in amount and is uniformly distributed throughout the cytoplasm.
These types of eggs are characteristic of mammals,including humans,as well as some other organisms like sea urchins and amphioxus.
In contrast,birds have telolecithal eggs (large amount of yolk),frogs have mesolecithal eggs (moderate amount of yolk),and insects have centrolecithal eggs (yolk in the center).

(D) Spermiogenesis is the process of transformation of spermatids into mature spermatozoa.
During this process,the heads of the developing sperm become embedded in the Sertoli cells to receive nutrition.
After the completion of spermiogenesis,the sperm are released from the seminiferous tubules by a process called spermiation.
Therefore,the correct option is $D$.

(B) The process of release of an ovum (secondary oocyte) from the Graafian follicle of the ovary is known as $Ovulation$.
This process typically occurs around the $14^{th}$ day of the menstrual cycle in a $28$-day cycle.
$Oviparity$ refers to the production of eggs that hatch outside the body.
$Incubation$ refers to the process of keeping eggs at a suitable temperature for development.