Lab report 4 GametogenesisGametogenesisGametogenesis(Science: biology) process leading to the production of gametes. The development andmaturation of sex cells through meiosis.Another name for meiosis where a diploid cell isdivided into two haploid cells with half the chromosome content of the diploid parent cell.

What is the function of the sperm's tail and sperm's head?The tail or flagella helps the sperm swim the log way from the vagina to the fallopian tube where it fertilizes the egg.

The head has an acrosome filled with stuff that can break down the fluid surrounding the egg and the head contains the genetic information needed to create a baby.---The sperm's head contains all of the haploid DNA of the father, as well as enzymes in the "acrosome" (pouch in the tip of the 'nose'- enables adhesion and breakdown of the zona pellucida surrounding the egg).

The tail generates propulsion to enable the sperm to navigate its way into the egg.----the head contain the chemicals needed to dissolve the egg's plasma membrane and contains genetic material to create a babyand the tail is fro helping the sperm to move----the head contains the genetic material that will be used to fuse with the egg and create the zygote/baby

the tail is used to propel the sperm forward....used for motility----Sperm or Spermatozoon; consists of 4 parts - Head, Neck, Middle Piece and Tail.Tail is very long, slender and tapering, and is formed of cytoplasm (though less in quantity but outside). Axoneme or Axial Filament occurs throughout. Tail is vibratile part of sperm.Main function of Tail; is the propulsion system. It is the whip-like structure of the sperm tail which serves the important function of propelling the sperm cell forward with a snake-like motion. It is critical that sperm move forward and not laterally or in circles. ---A mature sperm has a head, mid-piece, and tail.The sperm's whip-like tail propels the sperm forward with the energy produced by mitochondria in the mid-piece.--Sperm is manufactured in the seminiferous tubules within the testicle.----AnswerA sperm cell is the male reproductive cell. The tail is made of protein fibres that contract on alternative sides, giving a wavelike movement that drives the sperm through the seminal fluid, which also supplies additional energy. The most important function of the tail is propelling the sperm cell forward with a snake-like motion. This is critical because that sperm failure of sperm to move forward is described as an abnormality of sperm motility.---Helps the sperm swim and float. The tail is called cilia and it helps in the movement of the sperm. It makes it able to reach the egg.---it is to aid the sperm to swim from the point of ejaculation to the egg. Once it enters the egg the tail breaks off.---To help the sperm move and direct it.---The tail is called cilia and it helps in the movement of the sperm. It makes it able to reach the egg.

It is NOT cilia. It is a flagella.---Gene Carriers. A single sperm cell holds 18,000 genes. Each cell is covered in enzymes, which help it penetrate the egg. Energy Conversion. In order for sperm cells to work properly

Sperm CellSpermatozoa are a unique specialization of cells in men. A good way to describe a sperm cell is to think of it as an Apollo space shuttle, as each is comprised of three essential components; capsule, fuel tank, and propulsion unit.

The main function of the sperm is to carry the 18,000 male genes to the female’s egg, just as the Apollo capsule carries the astronauts on their mission. These genes represent the male's contribution to the DNA make-up of the hoped-for baby. The capsule also has a unique surface feature in its membrane which allows it to burrow through the shell of the woman's egg. Using the enzymes that are built into its surface, the sperm cell digests its way through the outer eggshell called the zona pellucida. The sperm cell is then able to enter into the main part of the egg, the ooplasm, achieving successful fertilization.The second component of the sperm cell is the energy source. Think of this as the rocket's fuel tank, its sole purpose is to convert nutrients into energy. Without this the propulsion system would not have the energy to take the cell up the female genital track. The third and final component of the sperm cell is the propulsion system. It is the whip-like structure of the sperm tail. It serves the important function of propelling the sperm cell forward with a snake-like motion. It is critical that sperm move forward and not laterally or in circles. The failure of sperm to move forward is described as an abnormality of sperm motility.

Structure and Function of the Sperm Cell Sperm are very, very small, only about .002 inches long, which is only that long because of its long tail-like flagella. Compared to the egg, one sperm is only 1/85,000th of the egg’s volume. The shape of the sperm is relatively simple. It has a small ovular head, connected to a long tail by a small part called the body. The function of the sperm is single-minded. When ejaculated, they are supposed to swim as fast as possible to the egg in the woman’s fallopian tube, where it then penetrates the outer part of the egg in order to start the meiosis process and create a unique individual of the two gene donors. The sperm is half of what is needed for reproduction in order to continue the human race. The tail of the sperm cell is a modified flagella, which is used as a propeller for the sperm to swim towards the egg. The flagellum has nine microtubules that run down the length of it, as well as a pair of microtubules that run down the center of the tail. The tail is moved by the use on an ATP-splitting enzyme called Ciliary Dynein. The enzyme is needed for the motility of flagella for it interacts with the microtubules and causes sporadic movement which propels the sperm. When homing in on the egg, the tail will move with more

frequency, which is needed to break past the physical barriers of the egg. While the sperm cell is not part of system or network of cells, the testes do make trillions of them for a good reason. In every ejaculate, there are about a quarter of a billion sperm. This is because not every sperm will be able to swim straight, or sometimes at all. Also, not every sperm cell will make it to the egg. Therefore, the more sperm that the gonads create and ejaculate, the higher the odds of conception.

Studies on the Function of the Annulus of the Sperm TailThe annulus on the sperm tail is critical for sperm function; Council research on the annulus may lead to the development of a novel, reversible male contraceptiveDuring spermatogenesis a round spermatogonium is transformed into a highly polarized, exceedingly streamlined spermatazoon that then must not only exist in several different environments of the male reproductive tract but in various environments of the female reproductive tract as well. Sperm must alter their function as they travel and, when they encounter the egg, undergo a series of modifications so fertilization can occur.One of the amazing feats of this process is that the sperm accomplish these modifications and alterations in function without generating new proteins. Most somatic cells change their function by altering the complement of proteins made. Sperm, however, do not have this option as they jettison their bulky synthetic machinery in one of the final stages of development to produce their sleek streamlined appearance. Sperm appear to compensate for their inability to synthesize new proteins by rearranging the distribution of their existing proteins at specific times thereby allowing new permutations of interaction that result in new biochemical reactions and modified function.In order for such a system to work sperm must have three basic components: (1) they must have a means of initially segregating their proteins thus producing a polarized cell; (2) they must have barriers (either physical structures or biophysical forces) that maintain these protein domains; and (3) they require a mechanism of transiently allowing redistribution of certain proteins from one domain to another. The most-studied proteins of this phenomenon are membrane-bound proteins, which will serve as the models for this discussion, but similar mechanisms may exist for cytoplasmic proteins as well. This project centers on the partitioning that goes on in the tail with the focus on the organelle—the annulus—that separates the midpiece domain and principal-piece domain.

GAMETOGENESIS

Professor Alfred CuschieriDepartment of Anatomy

University of Malta Objectiveso       Explain the significance and importance of meiosis in sexual reproductiono       Identify the different stages of gametogenesis in males and females in micrographs of testis and ovaryo       Name the stages at which the first and second meiotic divisions take placeo       Outline the stages of spermiogenesiso       Name the functions of Sertoli cells and granulosa cellso       Define the stages at which meiotic arrest in oocytes normally occurso       Identify the components of developing ovarian follicles and of the oocyte at the time of ovulationo       Discuss the mechanism of non-disjunction in numerical chromosome aberrations.  Sexual Reproduction Sexual reproduction involves the formation of male and female gametes  and the the mechanisms necessary for the gametes to come together and fuse to form one cell that represents the beginning of a new individual with a distinct genetic identity.Preparation for pregnancy involves two main programs of events:1. Gametogenesis  

o       the process of formation of the male and female gameteso       occurs in the gonads (ovary or testis)

2. Cyclic changes in the female genital tract  o       the ovarian cycleo       the uterine cycle

One Essential Question: Why is sexual reproduction  necessary?The main purpose of sexual reproduction is the formation of offspring who are genetically different from one another and from their parents.Meiosis is the fundamental process underlying sexual reproduction.  It involves two essential outcomes:1. Reduction Division the process in which each gamete receives a haploid set (n) of chromosomes and genes.The diploid number (2n) is restored on fusion of two gametes.2. Rearrangement of genes on the maternal and paternal chromosomes.This ensures that the offspring are genetically different  from one another.

 

Meosis involves four main events, and two cell divisions.  (In the following diagram only one pair of homologous chromosomes is shown, to represent 23 pairs in humans).      

     

DNA replication precedes meiosis, and occurs in the S phase, as in all cell divisions.  Recall that the chromosomes in the parent cell contains a diploid set of chromosomes (2n chromosome number and 2c amount of DNA).  Following replication, there are still 2n chromosomes, but each chromosome consists of two chromatids, and has 2c DNA.

   

2. Pairing of homologous chromosomes and crossing over of chromosome segments occur during prophase of meiosis. They are crucial event in meiosis.The complex of a homologous chromosome pair consisting of four chromatids is a tetrad.  The result of crossing over is that there are now fourrecombinant chromatids.

   3. Separation of chromosomes occurs as a result of the first meiotic division. The two resulting daughter cells each have one of a pair

ofreplicated chromosomes, or a haploid set (n) with a total of 2c DNA.  4. Separation of chromatids occurs as a result of the second meiotic division, and give rise to four daughter cells, each containing a haploid set of chromosomes (1n; 1c) amount ofMeiosis occurs in the germ cells.  As a result of meiosis, four daughter cells  or gametes, are produced, each containing one of a pair chromosomes and  all containing different chromosomes.  Although the above diagram illustrates only crossing over between the adjacent chromatids, in fact crossing over also occurs between the two “outer” chromatids, and at different sites from the other pair, so that all four daughter cells are different from one another and from their parents. Pairing of the two “outer” chromatids is possible because, in 3 dimensions these would also be adjacent to one another.  

Genetic ImprintingIn all diploid cells of an individual the chromosomes occur in homologous pairs.    One chromosome of each pair is derived from the mother and the other from the father. The maternal and paternal chromosomes are morphologically indistinguishable but have important functional implications because the expression of some genes is dependent on whether they are on the maternal or the paternal chromosome.  This is termed genetic imprinting GametogenesisGametogenesis is the process of formation of gametes from the germ cells in the testes and ovaries.   Many principles of gametogenesis are the same in both males and females, and will be considered first. Gametogenesis is divided into four phases: 1. Extra-gonadal origin of primordial germ cells2. Proliferation of germ cells by mitosis3. Meiosis4. Structural and functional maturation of the ova and spermatozoaPrimordial Germ Cells 

o       Are the earliest precursors of all germ cellso       Are formed in the early stages of embryonic developmento       Are first recognizable close to the hindgut as large cells with high alkaline phosphataseo       Proliferate and migrate into the gonad (testis or ovary)o       Differentiate into male or female germ cells (determined by sex chromosomes)

 The nomenclature of the developmental stages of gametogenesis is similar in male and female germ cells.  It is summarised in the following diagram. 

                                     In males the spermatids, the products of the second meiotic division, undergo morphological changes, known as spermiogenesis,  during which they become motile spermatozoa.  There is no corresponding stage in females.The timing of the developmental stages of gametogenesis, and the number of gametes produced are very different in male and female germ cells.

In the male spermatogenesis occurs from puberty to old age, producing immense numbers of spermatozoa at an average rate of 1.5 million spermatozoa per minute.

 o       In females oogenesis begins in early foetal life. All oocytes ever to be formed in females are produced during foetal life. Many of them

degenerate with time and at birth the ovaries contain about 2 million oocytes.   All the oocytes go into meiotic arrest when they reach the first meiotic division during foetal life. The primary oocytes remain in the prophase of the first meiotic division until the time of puberty, when they are gradually released to complete meiosis at regular intervals known as the ovarian cycle. On the average only one oocyte matures during each cycle, which occurs at approximately monthly intervals, so that the total amount of oocytes to be ovulated is about 500 oocytes in a lifetime.

SpermatogenesisSpermatogenesis is the process of formation of the male germ cells.  It occurs in the seminiferous tubules of the testes.  The developmental stages of the male germ cells can be observedsequentially from basement membrane to lumen.

 

The sertoli cells are supporting cells that have several functions.They form the blood-testes barrier: nutrients, and circulating substances do not directly reach the germ cells; the Sertoli cells determine which substances reach the germ cells. The spermatogonia are outside the blood-testis barrier.   They form invaginations surrounding the spermatocytes, spermatids and developing spermatozoa and are nutritive to them. They also produce antigen-binding proteins, which are necessay for spermiogenesis. The figure below is a light micrograph of  a seminiferous tubuleSpermiogenesis is morphological development of  spermatids to spermatozoa. It involves:

a.      Nuclear changes - The nucleus becomes condensed and heterochromatic -histones are replaced by protamines, which allow a high degree of DNA compaction and makes DNA inaccessible for transcription

Cytoplasmic changes – These are directed to the formation  of a  motile sperm cell capable of penetrating the ovum and involves the following changes:

 o       The Golgi apparatus at one pole of the cell forms an acrosome

containing proteolytic enzymeso       The centrriole at the opposite pole organises the formation of microtubules to

form a flagellumo       Alignment of mitochondria in a spiral around the base of the flagellum – this

forms the mid-piece of the spermatozoono       The excess residual cytoplasm accumulates at one side of the cell and becomes

detached to form a residual body  

OogenesisAt birth the ovary contains primordial follicles. They consist of a primary oocyte surrounded by granulosa cells.Gap junctions connect the oocyte to surrounding granulosa cells.The gap junctions permit passage of amino acids, glucose and metabolites for growth of the oocyte.The follicular cells secrete a meiotic inhibitory factor that is responsible for the first meiotic arrest.  The developing oocyte undergoes two meiotic arrests:

The Ovarian follicle consists of the following:               

      The zona pellucida:

o       Is  secreted by the oocyte

o       Consists of glycoprotein and glycosaminoglycanso       Contains sperm receptors necessary for fertilization

  

The oocyte cytoplasm contains:- numerous ribosomes (produced by r-DNA amplification in nucleolus)

- Yolk droplets ( nutritive)

- Cortical granules  (formed in the Golgi apparatus). Cortical granules are released on penetration of the vitelline membrane by a sperm. They cause a change in the zona pellucida to prevent double fertilization The Graafian follicle (tertiary follicle) is distended with liquor and points at the surface of the ovary like a blister. 

Rupture of the follicle occurs at ovulation releasing the secondary oocyte.  At the time of ovulation the second meiotic division is still not completed.  After ovulation the secondary oocyte is surrounded by a corona radiata.

  

Abnormalities in meiosis may give rise to numerical chromosome abnormalitites. Non-disjunction is the usual mechanism by which abnormalities in chromosome number may occur.  The following diagram illustrates chromosome 21 in meiosis I and II in (a) normal gametogenesis and (b) non-disjunction in meiosis I.  Failure of separation of the chromosomes results in a secondary oocyte or a secondary spermatocyte with two chromosomes 21, which will form trisomy 21 after fertilisation.  The other secondary oocyte or spermatocyte has does not contain a chromosome 21, and after fertilization, will result in monosomy 21.  This is incompatible with survival and this condition is therefore not seen.  Non-disjunction also occurs in common trisomies e.g. trisomy

18 or trisomy 13.Non-disjunction may also occur in meiosis II, resulting from failure of separation of the chromatids, as shown in the following diagram.  This type of non-disjunction is rare.  

OogenesisGo to:

Oogenic meiosisOogenesis—the differentiation of the ovum—differs from spermatogenesis in several ways. Whereas the gamete formed by spermatogenesis is essentially a motile nucleus, the gamete formed by oogenesis contains all the materials needed to initiate and maintain metabolism and development. Therefore, in addition to forming a haploid nucleus, oogenesis also builds up a store of cytoplasmic enzymes, mRNAs, organelles, and metabolic substrates. While the sperm becomes differentiated for motility, the egg develops a remarkably complex cytoplasm.The mechanisms of oogenesis vary among species more than those of spermatogenesis. This difference should not be surprising, since patterns of reproduction vary so greatly among species. In some species, such as sea urchins and frogs, the female routinely produces hundreds or thousands of eggs at a time, whereas in other species, such as humans and most mammals, only a few eggs are produced during the lifetime of an individual. In those species that produce thousands of ova, the oogonia are self-renewing stem cells that endure for the lifetime of the organism. In those species that produce fewer eggs, the oogonia divide to form a limited number of egg precursor cells. In the human embryo, the thousand or so oogonia divide rapidly from the second to the seventh month of gestation to form roughly 7 million germ cells (Figure 19.19). After the seventh month of embryonic development, however, the number of germ cells drops precipitously. Most oogonia die during this period, while the remaining oogonia enter the first meiotic division (Pinkerton et al. 1961). These latter cells, called the primary oocytes, progress through the first meiotic prophase until the diplotene stage, at which point they are maintained until puberty. With the onset of adolescence, groups of oocytes periodically resume meiosis. Thus, in the human female, the first part of meiosis begins in the embryo, and the signal to resume meiosis is not given until roughly 12 years later. In fact, some oocytes are maintained in meiotic prophase for nearly 50 years. As Figure 19.19 indicates, primary oocytes continue to die even after birth. Of the millions of primary oocytes present at birth, only about 400 mature during a woman's lifetime.

Spermatogenesis and OogenesisMeiosis, the process by which gametes are formed, can also be called gametogenesis, literally “creation of gametes.” The specific type of meiosis that forms sperm is called spermatogenesis, while the formation of egg cells, or ova, is called oogenesis. The most important thing you need to remember about both processes is that they occur through meiosis, but there are a few specific distinctions between them.SpermatogenesisThe male testes have tiny tubules containing diploid cells called spermatogonium that mature to become sperm. The basic function of spermatogenesis is to turn each one of the diploid spermatogonium into four haploid sperm cells. This quadrupling is accomplished through the meiotic cell division detailed in the last section. During interphase before meiosis I, the spermatogonium’s 46 single chromosomes are replicated to form 46 pairs of sister chromatids, which then exchange genetic material through synapsis before the first meiotic division. In meiosis II, the two daughter cells go through a second division to yield four cells containing a unique set of 23 single chromosomes that ultimately mature into four sperm cells. Starting at puberty, a male will produce literally millions of sperm every single day for the rest of his life.

OogenesisJust like spermatogenesis, oogenesis involves the formation of haploid cells from an original diploid cell, called a primary oocyte, through meiosis. The female ovaries contain the primary oocytes. There are two major differences between the male and female production of gametes. First of all, oogenesis only leads to the production of one final ovum, or egg cell, from each primary oocyte (in contrast to the four sperm that are generated from every spermatogonium). Of the four daughter cells that are produced when the primary oocyte divides meiotically, three come out much smaller than the fourth. These smaller cells, called polar bodies, eventually disintegrate, leaving only the larger ovum as the final product of oogenesis. The production of one egg cell via oogenesis normally occurs only once a month, from puberty to menopause.

Oogenesis occurs by meiosis as well, but with some modifications.   First of all, it would not be good for females to make millions of ova, since a female cannot carry millions of fetuses!  Instead, no more than one ovum per month should be made.  Because of this, females do not need to have constant mitosis of their germ cells occurring-- it is OK that once a germ cell is used it is not replenished.   Secondly, the ova need to contain a lot of nutrients (to get the embryo through its first set of divisions), so these cells need to be big.  Finally, it turns out that meiosis is only completed when producing an egg that is fertilized.  Let's go through these ideas a bit more.    In an ovary are millions of oocytes.  An oocyte is not the same thing as a germ cell.  The germ cells develop in the fetus and before birth begin meiosis, and then freeze right at the start of the first meiotic division.  These cells are stopped in prophase I of meiosis I, and are called primary oocytes.  They lie within the ovaries surrounded by other cells, the follicular cells.  The primary oocyte plus its follicular cells comprise the primary follicle.    Only when signalled by hormones, one single primary oocyte (of all those in both ovaries) picks up meiosis where it left off.  It finishes its first meiotic division.  It does this by dividing its genetic material appropriately for meiosis I, but then undergoing cytokinesis differently.    Cytokinesis is the physical separation of the daughter cells into two completely unattached cells.  It occurs via a cleavage furrow.  During mitosis and spermatogenesis, cytokinesis of the two daughter cells occurs right down the middle of the parent cell (symmetrical cytokinesis); but during oogenesis, cytokinesis occurs unevenly (asymmetrical cytokinesis).  This is shown for you in the following two animations:  Why is it important that asymmetrical cytokinesis occurs in oogenesis?  The primary oocyte is a very large cell containing many nutrients that will be important for the early mitotic divisions of the zygote (as it grows into an embryo).  When the cell divides during meiosis, only one of the daughter cells can become the ovum-- we only want one ovum per month!  So, the one cell that is destined to become the ovum (out of 4 potential daughter cells) is the only one that should get the nutrients.  And it should get ALL of the nutrients!  We want to start our zygote off well!  This means that the other cells do not need much of the nutrient-rich cytoplasm.  These tiny other cells are called polar bodies, and they do not last long.  Polar bodies die pretty quickly.  Just the ovum survives.    The large cell in the picture above is either the product of the first or second meiotic division that lives.  If it is the product of the first meiotic division (where the parent cell was the primary oocyte) it is called the secondary oocyte.  If it is the product of the second meiotic division (where the parent cell was the secondary oocyte) it is called the ovum.   The terms secondary oocyte and ovum are NOT interchangeable-- they are different.    OK.  Now let's get through all of meiosis.   Females start off with millions of primary oocytes.  Every month, one of these primary oocytes is hormonally stimulated to begin to enlarge and to complete the first meiotic division.  (As it enlarges, the entire follicle enlarges-- this is shown in the ovulation web page... but the polar body is not included in the animation there).   The oocyte is now a secondary oocyte, and its polar body will degenerate.  The secondary oocyte is released from the ovary.    Once the secondary oocyte exits the ovary, it begins to travel down the uterine (fallopian) tube.  If it does not encounter a spermatozoan, it never undergoes the second meiotic division.  The second meiotic division only occurs when fertilization happens.  That means that I, since I have never gotten pregnant, I have never had any of my oocytes finish meiosis!  However, if the secondary oocyte comes in contact with a spermatozoan and fertilization begins, the secondary oocyte undergoes its second meiotic division to form the ovum (and another polar body).  Now the ovum is ready to fuse with the spermatozoan.SpermatogenesisSpermatogenesis is the process by which male primordial germ cells called spermatogonia undergo meiosis, and produce a number of cells termedspermatozoa. The initial cells in this pathway are called primary spermatocytes. The primary spermatocyte divides into two secondary spermatocytes; each secondary spermatocyte then divides into two spermatids. These develop into mature spermatozoa, also known as sperm cells. Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa.[1]

Spermatozoa are the mature male gametes in many sexually reproducing organisms. Thus, spermatogenesis is the male version of gametogenesis. Inmammals it occurs in the male testes and epididymis in a stepwise fashion, and for humans takes approximately 64 days.[2] Spermatogenesis is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. DNA methylation and histone modification have been implicated in the regulation of this process.[3] It starts at puberty and usually continues uninterrupted until death, although a slight decrease can be discerned in the quantity of produced sperm with increase in age (see Male infertility).Purpose [edit]

Spermatogenesis produces mature male gametes, commonly called sperm but specifically known asspermatozoa, which are able to fertilize the counterpart female gamete, the oocyte, during conceptionto produce a single-celled individual known as a zygote. This is the cornerstone of sexual reproduction and involves the two gametes both contributing half the normal set of chromosomes(haploid) to result in a chromosomally normal (diploid) zygote.To preserve the number of chromosomes in the offspring – which differs between species – each gamete must have half the usual number of chromosomes present in other body cells. Otherwise, the offspring will have twice the normal number of chromosomes, and serious abnormalities may result. In humans, chromosomal abnormalities arising from incorrect spermatogenesis can result in Down Syndrome, Klinefelter's Syndrome, and spontaneous abortion.Location [edit]

Spermatogenesis takes place within several structures of the male reproductive system. The initial stages occur within the testes and progress to the epididymis where the developing gametes mature and are stored until ejaculation. The seminiferous tubules of the testes are the starting point for the process, where stem cells adjacent to the inner tubule wall divide in a centripetal direction—beginning at the walls and proceeding into the innermost part, or lumen—to produce immature sperm. Maturation occurs in the epididymis.Stages 

The process of spermatogenesis. 1. Primary spermatocyte 2. Secondary spermatocytes 3. Spermatids 4. SpermThe entire process of spermatogenesis can be broken up into several distinct stages, each corresponding to a particular type of cell in human:

Cell type ploidy/chromosomes in human DNA copy number/chromatids in human Process entered by cell

spermatogonium (types Ad, Ap and B)

diploid (2N) / 46 2C / 46 spermatocytogenesis(mitosis)

primary spermatocyte diploid (2N) / 46 4C / 46 spermatidogenesis (meiosis1)

two secondary spermatocytes haploid (N) / 23 2C / 46 spermatidogenesis (meiosis2)

four spermatids haploid (N) / 23 1C / 23 spermiogenesis

four functional spermatozoids haploid (N) / 23 1C / 23 spermiation

Ploidy and chromosome counts are for one cell in G1, prior to DNA synthesis and division

Role of Sertoli cells 

Labelled diagram of the organisation of Sertoli cells (red) and spermatocytes (blue) in the testis. Spermatids which have not yet undergone spermination are attached to the lumenal apex of the cellMain article: Sertoli cellAt all stages of differentiation, the spermatogenic cells are in close contact with Sertoli cells which are thought to provide structural and metabolic support to the developing sperm cells. A single Sertoli cell extends from the basement membrane to the lumen of the seminiferous tubule, although the cytoplasmic processes are difficult to distinguish at the light microscopic level.Sertoli cells serve a number of functions during spermatogenesis, they support the developing gametes in the following ways: Maintain the environment necessary for development and maturation, via the blood-testis barrier Secrete substances initiating meiosis Secrete supporting testicular fluid Secrete androgen-binding protein (ABP), which concentrates testosterone in close proximity to the developing gametes

Testosterone is needed in very high quantities for maintenance of the reproductive tract, and ABP allows a much higher level of fertility Secrete hormones affecting pituitary gland control of spermatogenesis, particularly the polypeptide hormone, inhibin Phagocytose residual cytoplasm left over from spermiogenesis They release Antimullerian hormone which prevents formation of the Müllerian Duct / Oviduct. Protect spermatids from the immune system of the male, via the blood-testis barrierThe intercellular adhesion molecules ICAM-1 and soluble ICAM-1 have antagonistic effects on the tight junctions forming the blood-testis barrier.[5] ICAM-2  molecules

regulate spermatid adhesion on the apical side of the barrier (towards the lumen).[5]

SPERMATOGENESISSpermatogenesis is the process of sperm cell development. Rounded immature sperm cells undergo successive mitotic and meiotic divisions (spermatocytogenesis) and a metamorphic change (spermiogenesis) to produce spermatozoa.Mitosis and meiosis. Mitosis is the process of cell duplication - two daughter cells are formed with exactly the same DNA and chromosomal content of the original diploid (2N) mother cell. Human cells contain 46 chromosomes - 22 pairs of homologous autosomes and one pair of sex chromosomes.Mitosis (M) encompasses just one step in the eukaryotic cell cycle: G1 > S > G2 > M > C. Cells grow during the dominant G1 phase. Replication of chromosomes occurs in the S phase. Preparation for mitosis takes place during G2 - replication of organelles and synthesis of microtubules. Interphase includes the combined stages G1, S, and G2. During mitosis: chromosomes condense, the nuclear envelope disappears, and spindle fibers begin to form from microtubules (prophase); centromeres of duplicate sister chromatids align along the spindle equator (metaphase); chromatids separate and migrate toward opposite poles (anaphase); the mitotic apparatus is disassembled, autonomous nuclear envelopes are established, and the chromosomes uncoil (telophase). The final stage of the cell cycle, when cell division actually occurs, is called cytokinesis (C).Meiosis is a special process of reductional cell division; it results in the formation of four gametes containing half (1N) the number of chromosomes found in somatic cells. Haploid gametes unite at fertilization to create a diploid zygote. Remember that in mammals the heterogametic male (XY) determines the sex of the embryo. Approximately one-half of spermatozoa contain either an X or Y chromosome (the sex chromosomal complement of mammalian females is XX, and therefore, ova can only contribute an X chromosome to the offspring). Genes carried on the X chromosome that inhibit spermatogenesis are inactivated in XY somatic cells.Steps of meiosis are outlined in Table 3-3. Meiosis differs from mitosis in two critical respects. During prophase of meiosis I, chromosomes pair along their length and come in contact in discrete areas of synapsis (chiasmata). Chromatids can exchange base pairs by crossing-over. The recombination of segments of chromosomes allows for continual generation of genetic variability (ie., rapid evolutionary progress) and provides a mechanism for correcting damage in the DNA helix. Secondly, nonidentical sister chromatids do not replicate between serial nuclear divisions. Meiosis II is essentially mitotic.(An unusual natural circumstance exists in the creeping vole - males normally have OY gametes; the X chromosome is eliminated from the cell line by nondisjunction and the companion XXY cell presumably does not complete meiosis [in most mammals OY is lethal]).Spermatocytogenesis. During spermatocytogenesis primitive cells called spermatogonia proliferate by mitosis. Several different types of spermatogonia have been identified (A-0 through A-4, intermediate [IN], and B). Only the discriminating anatomist can actually distinguish among types of spermatogonia. Mitosis ends when a B spermatogonium yields two primary spermatocytes.The diploid number of primary spermatocytes is halved during meiosis. A primary spermatocyte is transformed into two secondary spermatocytes during meiosis I - these cells then in turn are converted into (1N) spermatids during meiosis II. The second meiotic division is rapid (and therefore very few secondary spermatocytes can be identified in histological sections). Spermatocytes and spermatids tend to be larger than their ancestral spermatogonia.Males have an almost unlimited capacity to produce germ cells; this is accomplished by replenishment of A spermatogonia early in mitosis. Although the mechanics of renewal are not totally understood, it appears that a stem cell (A-0) divides into an A-1 spermatogonia and an operative copy of itself. The A-1 cell becomes dedicated to spermatocytogenesis and the A-0 cell is kept in reserve for future divisions.Endogenous damage to the the genetic material (eg., base deamination, depurination, methylation, oxidative insult) is inevitable in proliferative cells - a battery of repair mechanisms assure that the DNA fidelity of gametes is sustained.

Lecture 3: Spermatogenesis What is spermatogenesis?Overview:1.   Spermatogenesis is the process of producing sperm with half the number of chromosomes (hapliod) as somatic cells.

a.         The germ cells progress first from the diploid to haploid state and then change shape to become spermatozoa.2.  The process of spermatogenesis then allows the recombination of male and female haploid gametes at fertilization.3.  This provides genetic contributions from both parents without increasing the number of chromosomes each generation.Where does spermatogenesis occur?

1. Spermatogenesis occurs in medullary sex cords known as seminiferous tubules.2. Seminiferous tubules are part of the male gonad or testes.

Cells involved in spermatogenesis.1.         Sertoli cells—“nurse cells”

a.         Nurse cells provide:                        i.          Support for germ cells                        ii.         Environment for germ cells to develop and mature                        iii.       Substances initiating meiosis or the reduction from diploid to haploid cells                        iv.        Hormonal signals effecting pituitary gland control of spermatogenesis            b.         Sertoli cells divide the seminiferous tubules into two environments for the development of spermatozoa

i.          Basal compartment is the space in which spermatogonia develop to primary spermatocytesii.         Adluminal compartment is

            c.         Sertoli cells produce hormones                        i.          Estrogen

                        ii.         Inhibin—suppresses pituitary FSH2.         Leydig cells            a.         Produce testosterone

b.         Located adjacent to seminiferous tubules.Spermatogenesis in the Sexually Mature Male1.         Function of the testes is to produce the male gametes or spermatozoa

a.         This process is termed, spermatogenesisb.         The site of spermatozoa production is the seminiferous tubules

2.         The spermatozoa originate from precursor cells that are called spermatogoniaa.         These cells line the basement membrane of the seminiferous tubule

3.         Spermatogenesis can be divided into three parts:            a.         Spermatocytogenesis—proliferative phase            b.         Meiosis—production of the haploid gamete            c.         Spermiogenesis

i.          Spermatids mature into spermatozoa (sperm)4.         The adult male mammal that is a continuous breeder.

a.         Males continue to produce spermatozoa throughout life. Spermatocytogenesis and Meiosis1.         Spermatogonia divide

a.         Located near outer surface of seminiferous tubuleb.         Originate at pubertyc.         One or two divisions of spermatogonia occur to maintain their population in a stem cell pool (type A spermatogonia)d.         These divisions are mitotice.         Spermatogonia proliferate several times and undergo 1 to 5 stages of division and differentiationf.          After the last division, the resulting cells are termed primary spermatocytes

2.         The primary spermatocytes then undergo the first of the two divisions that constitute meiosisa.         The first meiotic division produces two secondary spermatocytesb.         Division of the secondary spermatocytes completes meiosis and produces the spermatids 

3.         Stem cell spermatogonia remain dormant for a time and then join a new proliferation of spermatogoniaa.         This new wave of spermatogonial divisions does not wait for the previous generation of cells to complete spermatogenesis

i.          The purpose of this phenomenon is to ensure a residual population of spermatogoniab.         The time required for one spermatogonium to divide and form spermatozoa requires about 4.5 to 5 times that time span between divisions of the stem cell

spermatogonia Spermiogenesis: morphological conversion of round spermatid into spermatozoa without a division 1.         This part of spermatogenesis is defined as the nuclear and cytoplasmic changes in the spermatid that results in the spermatozoa2.         Events associated with spermiogenesis:            a.         Condensation of nuclear material            b.         Removal of extraneous cytoplasm            c.         Formation of the acrosome            d.         Formation of tail structures3.         Spermiogenesis ends in the testis with release of the spermatozoa from the Sertoli cell

a.         Throughout spermiogenesis, spermatozoa are embedded Sertoli cellsb.         The process by which spermatozoa are shed into the lumen of the seminiferous tubule for transport out of the testis is spermiation

 What is the overall result of spermatogenesis?1.         The overall result of spermatogenesis:             a.         Cell proliferation                        i.          More cells are produced than originally present                        ii.         Each spermatogonia may produce up to 256 spermatozoa per cycle (25 x 4)            b.         Maintenance of a reserve germ cell population                        i.          Production of new spermatogonia is faster than maturation of spermatozoa            c.         Haploid gametes are produced            d.         Genetic variability is introduced                        i.          Independent assortment during meiosis                        ii.         Crossing-over during Prophase I of meiosis            e.         Spermatids mature into spermatozoa Hormonal Control of Spermatogenesis

1.         Hormones that affect spermatogenesisa.         Testosterone            i.          Produced by Leydig cells            ii.         Androgen            iii.       Promotes Sertoli cell functionb.         Estradiol            i.          Produced by Sertoli cellsc.         Inhibin            i.          Produced by Sertoli cells            ii.         FSH levels in males is decreased by inhibind.         FSH—follicle stimulating hormone            i.          Produced by anterior pituitary            ii.         FSH regulates the mitotic divisions and efficiency of type A spermatogonia development            iii.       FSH controls entry of stem cell type A spermatogonia into proliferating pool

iv.        The yield of spermatozoa is increased by FSH by preventing the degeneration of differentiating A type spermatogonia            v.         FSH is necessary during development: required to establish Sertoli cell functione.         LH—lutenizing hormone            i.          Produced by anterior pituitary            ii.         Increases testesterone production by Leydig cellsf.          GnRH—gonadotropic releasing hormone

                        i.          Hypothalamic hormone that controls release of anterior pituitary hormones (LH and FSH)

2.         Once the Sertoli function is developed, testosterone alone will maintain spermatogenesis            a.         The yield of spermatozoa is increased if FSH is present Spermatogonia are labile1.         Degeneration of germ cells effected by:            a.         Season                        i.          Reflects hormonal and temperature cycles            b.         Disease            c.         Trauma or heat                        i.          Germ cells are temperature sensitive                        ii.         Testes are external structures to maintain a lower temperature            d.         Hormonal                        i.          Effects of FSF and inhibin Capacity for Sperm Production1.         Species dependent2.         Size of testis3.         Sperm produced/gm of tissue            a.         Involves length and efficiency of spermatogenesis4.         Daily sperm production            a.         Involves both size of testis and sperm produced/gm of tissue            b.         Boar best followed by ram, human is poor

 -------------------------------------------------------------------------------------------------------------------------------------------------

Spermatogenesis is initiated in the male testis with the beginning of puberty. This comprises the entire development of the spermatogonia (former primordial germ cells) up to sperm cells. The gonadal cords that are solid up till then in the juvenile testis develop a lumen with the start of puberty. They then gradually transform themselves into spermatic canals that eventually reach a length of roughly 50-60 cm. They are termed convoluted seminiferous tubules (Tubuli seminiferi contorti) and are so numerous and thin that in an adult male testicle their collective length can be 300 to 350 meters. They are coated by a germinal epithelium that exhibits two differing cell populations: some are sustentacular cells (= Sertoli's cells) and the great majority are the germ cells in various stages of division and differentiation. The development of the germ cells begins with the spermatogonia at the periphery of the seminal canal and advances towards the lumen over spermatocytes I (primary spermatocytes), spermatocytes II (secondary spermatocytes), spermatids and finally to mature sperm cells.

OogenesisOogenesis, ovogenesis or oögenesis / ̩ oʊ . ə ̍ dʒ ɛ n ɨ s ɪ s / [1]  is the creation of an ovum (egg cell). It is the female form of gametogenesis; the male equivalent is spermatogenesis. It involves the development of the various stages of the immature ovum.Oogenesis in mammals [edit]

Diagram showing the reduction in number of thechromosomes in the process of maturation of theovum. (In mammals, the first polar body normally disintegrates before dividing, so only two polar bodies are produced.)In mammals, the first part of oogenesis starts in the germinal epithelium, which gives rise to the development of ovarian follicles, the functional unit of the ovary.Note that this process, important to all animal life cycles yet unlike all other instances of cell division, occurs completely without the aid of oo spindle-coordinating centrosomes.[2][3]

Oogenesis consists of several sub-processes: oocytogenesis, ootidogenesis, and finally maturation to form an ovum (oogenesis proper).Folliculogenesis is a separate sub-process that accompanies and supports all three oogenetic sub-processes.

Cell type ploidy Process Process completion

Oogonium diploid Oocytogenesis (mitosis) third trimester (forming oocytes)

primary Oocyte diploid Ootidogenesis (meiosis 1) (Folliculogenesis) Dictyate in prophase I for up to 50 years

secondary Oocyte haploid

Ootidogenesis (meiosis 2) Halted in metaphase II until fertilization

Ovum haploid

Oogonium —(Oocytogenesis)—> Primary Oocyte —(Meiosis I)—> First Polar Body (Discarded afterward) + Secondary oocyte —(Meiosis II)—> Second Polar Body (Discarded afterward) + OvumThe creation of oogonia [edit]The creation of oogonia traditionally doesn't belong to oogenesis proper but, instead, to the common process of gametogenesis, which in the female human begins with the processes of folliculogenesis, oocytogenesis, and ootidogenesis.Human oogenesis [edit]

At the start of the menstrual cycle, some 12-20 primary follicles begin to develop under the influence of elevated FSH to form secondary follicles. The primary follicles have formed from primordial follicles, which developed in the ovary at around 10–30 weeks after conception. By around day 9 of the cycle, only one healthy secondary follicle remains, with the rest having undergone ovarian follicle atresia. The remaining follicle is called the dominant follicle and is responsible for producing large amounts of estradiol during the late follicular phase. Estradiol production depends upon co-operation between the theca and granulosa cells. On day 14 of the cycle, an LH surge occurs, which itself is triggered by the positive feedback of estradiol. This causes the secondary follicle to develop into a tertiary follicle, which then ovulates some 24–36 hours later. An important event in the development of the tertiary follicle occurs when the primary oocyte completes the first meiotic division, resulting in the formation of a polar body and a secondary oocyte. The empty follicle then forms a corpus luteum which later releases progesterone hormone

At which pole of the egg is the nucleus located?Egg has two pole animal pole and the vegetal pole. The nucleus is located in the animal pole, which occupies the upper hemisphere. It is darker than the lower vegetal part. http://users.rcn.com/jkimball.ma.ultrane…

Read it..... ( example frog's egg)

The frog egg is a huge cell; its volume is over 1.6 million times larger than a normal frog cell. During embryonic development, the egg will be converted into a tadpole containing millions of cells but containing the same volume of material. The upper hemisphere of the egg — the animal pole — is dark. (with nucleus)--------------------------------------…The lower hemisphere — the vegetal pole — is light. 

When deposited in the water and ready for fertilization, the haploid egg is at metaphase of meiosis -------Sperm in animals

Anatomy of SpermThe mammalian sperm cell consists of a head, a midpiece and a tail. The head contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an acrosome, which contains enzymes used for penetrating the female egg. The midpiece has a central filamentous core with many mitochondria spiralled around it, used for ATP production for the journey through the female cervix, uterus and uterine tubes. The tail or "flagellum" executes the lashing movements that propel the spermatocyte.[citation needed]

During fertilization, the sperm provides three essential parts to the oocyte: (1) a signalling or activating factor, which causes the metabolically dormant oocyte to activate; (2) the haploid paternal genome; (3) the centrosome, which is responsible for maintaining the microtubule system.[1]

Gametogenesis: The development and production of the male and female germ cells required to form a new individual.The male and female germ cells are called gametes. The gametes in human males are produced by the testes, two globe-shaped reproductive organs just below the penis. Male gametes are what most people refer to as sperm. Gametes in human females are produced by the ovaries, two oblong organs on each side of the uterus in the lower abdomen. Female gametes are what most people refer to as eggs or ova. During sexual intercourse, an ejaculated sperm cell penetrates an egg and unites with it (fertilizes it). The fertilized egg is called the zygote.The reproductive organs in both males and females (testes and ovaries, respectively) begin gametogenesis with a primitive germ cell. A primitive germ cell is a seed cell. Like a seed planted in a garden, a primitive germ cell initiates the process that eventually results in a new being. The primitive germ cell contains 46 pairs of chromosomes. Chromosomes are structures that hold the genetic information (the DNA) that determine the makeup of the new being. In humans, chromosomes influence hair, eye and skin color, height, bone structure -- indeed, all of the characteristics that prompt people to say that a child "takes after" his mother or father.Chromosomes occur in pairs because they reflect the makeup of the previous generation -- 23 chromosomes from the father and 23 from the mother. However, the gametes produced by the testes and the ovaries cannot each contain 46 chromosomes. Otherwise, after they unite, they will contain 92 chromosomes! Thus, the germ cells produced by the testes and ovaries each divide once, then divide again, in a reduction process that creates cells containing 23 chromosomes, or half the original number. The body is smart (or has evolved to do what it needs to do). This reduction process is known as meiosis.Then, after a male ejaculates sperm into a female and fertilizes her egg, a new individual with 46 chromosomes begins to form. In other words,pregnancy occurs."Gamete" is derived from the Greek word "gamete" (wife) and "gamein" (to marry). "Genesis" is derived from the Greek word "genein" (to produce). Thus, in gametogenesis, cells marry ("gamein") and produce ("genein") a new being. The first book of the Bible is called "Genesis" because it provides a figurative account of the beginning of humankind. Other words from Greek and Latin that contain "gen" (indicating production or output) include "generate," "genitals," and "generous." The word "gentry" means "of high or noble birth."

Gametogenesis  is the production of gametes. Spermatogenisis is the development of mature sperm, which occurs through celldivision and maturation within the seminiferous

tubules. The process of production of a single sperm is roughly seven weeks. Mature oocytes are formed in a long (in humans) process called oogenesis. Although ovaries contain immature eggs, these may not

complete their development for years. In the process of meiosis, spermatogenesis produces four mature gametes. In contrast, oogenesis involves unequal cytokinesis, with

all cytoplasm going to one large daughter cell (precursor to egg). The other three daughter cells disintegrate. In males, spermatogenesis occurs from adolescence to adulthood, while in females, the mitotic divisions of oogenesis occur before

birth, and mature gameteproduction ends about age 50. Spermatogenesis is a continuous process and is always ongoing in the male, while long breaks occur between periods of oogenesis in

the female.

gametogenesis 

The process by which gametes are produced.

spermatogenesis 

The process of sperm production in the testes.

oogenesis 

The formation and development of an ovum (female egg).

EXAMPLES While the sperm and egg serve the same purpose - each contributing half the genetic material to the offspring - there are numerous

differences between the sperm and egg, due to their different roles in fertilization. Sperm lack many of the materials most cells need to sustain growth. They have a nucleus carrying DNA and large numbers of mitochondria but very little compared to the egg, which has a full complement of organelles and a store of substrates and enzymes. This makes sperm fairly short-lived, while the egg is capable of sustaining itself, both before and after fertilization, for quite some time. The egg is also much larger than the sperm as it contains many additional structures that will be needed post-fertilization. The sperm are also motile, while the egg is not, as sperm must use their flagella to swim to the egg in order for fertilization to take place.

Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids, following their individual pathways. The oocytes and spermatocytes are both gametocytes. Ova and spermatids are complete gametes. In reality, the first polar body typically dies without dividing.

Gametogenesis is the development of diploid germ cells into either haploid eggs or sperm (oogenesis and spermatogenesis). Oogenesis and spermatogenesis have many features in common including meiosis, but they differ in major ways as well. Spermatogenesis has equivalent meiotic divisions resulting in four equivalent spermatids while oogenic meiosis is asymmetrical because only one egg is formed together with three polar bodies. Also, there is a difference in timing of maturation. Oogenic meiosis is interrupted at one or more stages (for a long time) while spermatogenic meiosis is rapid and uninterrupted.Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes or by mitotic division of haploid gametogenous cells. For example, plants produce gametes throughmitosis in gametophytes. The gametophytes grow from haploid spores after sporic meiosis. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations.Spermatogenesis is the process by which male primary germ cells undergo division and produce a number of cells termed spermatogonia, from which the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two spermatids or young spermatozoa. These develop into mature

spermatozoa, also known as sperm cells. Therefore, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa. Spermatozoa are the mature male gametes in many sexually reproducing organisms. Thus, spermatogenesis is the male version of gametogenesis.

Spermatogenesis produces mature male gametes, commonly called sperm but specifically known as spermatozoa, which are able to fertilize the counterpart female gamete, the oocyte, during conception to produce a single-celled individual known as a zygote. This is the cornerstone of sexual reproduction and involves the two gametes both contributing half the normal set of chromosomes (haploid) to result in a chromosomally normal (diploid) zygote. To preserve the number of chromosomes in the offspring – which differs between species – each gamete must have half the usual number of chromosomes present in other body cells. Otherwise, the offspring will have twice the normal number of chromosomes and serious abnormalities may result. In humans, chromosomal abnormalities arising from incorrect spermatogenesis can result in Down Syndrome, Klinefelter's Syndrome, and spontaneous abortion. Spermatogenesis takes place within several structures of the male reproductive system. The initial stages occur within the testes and progress to the epididymis where the developing gametes mature and are stored until ejaculation. The seminiferous tubules of the testes are the starting point for the process where stem cells adjacent to the inner tubule wall divide in a centripetal direction—beginning at the walls and proceeding into the innermost part, or lumen—to produce immature sperm. Maturation occurs in the epididymis.Oogenesis or oögenesis is the creation of an ovum (egg cell). It is the female form of gametogenesis. The male equivalent is spermatogenesis. It involves the development of the various stages of the immature ovum. In mammals, the first part of oogenesis starts in the germinal epithelium which gives rise to the development of ovarian follicles, the functional unit of the ovary. Oogenesis consists of several sub-processes: oocytogenesis, ootidogenesis, and finally maturation to form an ovum (oogenesis proper). Folliculogenesis is a separate sub-process that accompanies and supports all three oogenetic sub-processes. At the start of the menstrual cycle, some 12-20 primary follicles begin to develop under the influence of elevated FSH to form secondary follicles. The primary follicles have formed from primordial follicles, which developed in the ovary at around 10–30 weeks after conception. By around day nine of the cycle, only one healthy secondary follicle remains, with the rest having undergone cellular atresia. The remaining follicle is called the dominant follicle and is responsible for producing large amounts of oestradiol during the late follicular phase. Oestradiol production depends upon co-operation between the theca and granulosa cells. On day 14 of the cycle, an LH surge occurs, which is triggered by the positive feedback of oestradiol. This causes the secondary follicle to develop into a tertiary follicle, which then ovulates some 24–36 hours later. An important event in the development of the tertiary follicle occurs when the primary oocyte completes the first meiotic division, resulting in the formation of a polar body and a secondary oocyte. The empty follicle then forms a corpus luteum.