1-Give short notes on the spermatid maturation (spermiogenesis).

Spermatid maturatio(spermiogenesis):The task of the mature spermatozoon is to carry to

and introduce into the egg the genetic material of the

male parent.

The spermatids undergo complex process

of differentiation to form spermatozoa:

a-Formation of head:

-The nucleus shrinks. The acrosome is derived from Golgi

complex. It appears as a small vacuole containing a small

acrosomal granule.

-The remaining part of Golgi is removed from

sperm together with cytoplasm as residual bodies.

b-Neck region:

-It is a small region that connects the head to the

middle piece. It contains the proximal and distal

centrioles. The distal centriole gives rise to the axial filament

of flagellum (axoneme). The latter consists of two central tubules

surrounded by nine pairs of tubules or “doublets”.

c-Middle piece: It consists of flagellum surrounded by

Mitochondrial element and nine dense fibers.

d-The tail:

The tail is differentiated into two regions:

a-Principal piece: The axoneme is surrounded by seven dense fibers.

b-End piece: The axoneme is covered by a thin layer of cytoplasm and its plasmalemma.

•

2-Discuss the factors which control spermatogenesis.

The spermatogenesis is controlled by:

1-Hormonal factors:

The formation of mature Spermatozoon does not take

place until the age of puberty. The spermatogenic and

secretory functions of the testis are under the control of

the following pituitary gonadotrophins:

-LH hormone: stimulates the interstial cells to secrete

testosterone which stimulates spermatogenesis and

maintains the sex glands.

-FSH hormone: stimulates spermatogenesis in the

seminiferous tubules.

The negative-feedback effect of testosterone on

hypothalamus regulates the secretion of LH and FSH

2-Non-hormonal factors:

a-Temperature: elevation of body temperature may

destruct the spermatogenic cells.

b-Irradiation: x-rays and gamma rays destruct

spermatozoa.

c-Dietary factors: protein and vitamin A & E

deficiencies depress spermatogenesis.

d-Chemicals: numerous chemicals (lead, cadmium

…etc) destruct spermatogenic cells.

3-Write on the factors responsible for the male infertility

The factors responsible for male infertility are:

1-Semen volume: The main volume is about 3 milliliters.

There does not seem to be too much relation between

volume and ease of conception.

6

2-Sperm density: American Fertility Society proposed 40 X 10

6

sperm / ml as the normal minimum number. Below 10 X 10

sperm / ml the human should considered infertile.

3-Sperm motility: Motility of the sperm is important when the

sperm reach the ovum, vigorous movement is necessary to

penetrate the membranes surrounding the egg.

4-Sperm morphology: Morphologically, not all spermatozoa are

normal. If the percentage of abnormal spermatozoa exceeds

20% impaired fertility may be expected.

4-Give an account of the previtellogenesis growth period of the oocyte.

Previtellogenesis includes:

a-Growth of nuclear substances:Simultaneously, with the growth of oocyte its nucleus increases in size. The chromosomes

may increase in length but the amount of DNA does not increase.

b-Growth of cytoplasmic substanses:The amount of cytoplasm increases in quantity and in quality by the elaboration and regular distribution

of various inclusions.

-Large amount of RNA is present in cytoplasm.

-The mitochondria are increased in number.

-The Golgi complex besides performing its normal function manufactures the cortical granules.

The cortical granules

These are spherical bodies containing acid mucopolysacchrides for the synthesis of fertilization

membrane during fertilization.

5-Write on the vitellogenesis growth period of the oocyte.

Vitellogenesis:

It is the period of rapid growth in which the cytoplasm

is packaged by reserve food materials as glycogen,

carbohydrates, lipids and proteins all of which called

yolk or vitellin.

Vitellogenesis begins after the oocyte enters the

first prophase stage of maturation division.

In cephalochordates, most of the yolk is

proteinaceous. By contrast, less than 50% of the

dry weight of mature egg cell is yolk protein and

lipid costitute 25% of the dry weight of amphibian

egg.

Avian yolk is a combination of proteins (16.6%),

phospholipids (32.6%), carbohydrates(1%) and

vitamins.

The precursors of protein yolk are

manufactured outside the primary oocyte. The

vitellogenin is synthesized and secreted by liver

cells and transformed by blood to the follicle cells.

It passes through follicle cells and is incorporated

into the oocyte by micropinocytosis. The vitellogenin is

cleaved into two major yolk proteins, lipovitellin and

phosvitin.

6-Write on the different kinds of egg membranes.Oogenesis is followed by the formation of some

protective membranes around the plasma membrane of egg.

1-Primary egg membranes:

These are membranes which are formed by the egg.

a-Vitelline membrane:The primary envelop surrounds

eggs of insects, amphibia and birds.It is composed

of mucopolysacchrides and fibrous proteins

b-Zona radiata: it is a striated envelops surrounding the

eggs of shark, some bony fishes, amphibians and reptiles.

c-Zona pellucida: it is unstriated layer and is formed by joint

efforts of ova and follicle cells (e.g. mammalian egg).

2-Secondary egg membranes:

These membranes are formed by the follicle cells.

They are chitinous shells surrounding the eggs of

insects (chorion), ascidians and cyclostomes.

3-Tertiary egg membranes:

These membranes are formed by the oviduct and

other genital organs.

a-In oviparous shark: the egg is surrounded by

albumen and horny capsule secreted by shell gland.

b-In amphibian forms: the eggs are surrounded by jelly

coats secreted from oviduct.

c-In avian forms: the albumen, shell membranes and the

calcareous porous shell are formed by the oviduct.

7-Give a brief account of the hormonal control of ovulation.

In mammals, both the growth of follicle and the formation

of corpus luteum are controlled by the following hormones:

a-Follicle-stimulating hormone (FSH): stimulates the

growth of ovarian follicles and their secreting of estrogen.

b-Lutenizing hormone (LH): induces ovulation of mature

ovum and conversion of a Graafian follicle into a corpus

luteum. The pituitary gland, in turn, is influenced by two ovarian

hormones, estrogen and progesteron. The feedback from

the ovary to the pituitary gland may be positive (resulting in

an increase in the release of trophic hormones) or negative

(resulting in a decrease).

FSH, with a little LH, stimulates follicular growth

and production of estrogen in the ovary. The estrogen acts

upon the pituitary to secrete LH & LTH and to decrease

secretion of FSH. When corpora begin to regress, the

amounts of ovarian hormones are reduced and pituitary

again produces FSH to initiate reproduction of the ovarian

cycle. During pregnancy, the corpus luteum persists and there

is no follicular growth or ovulation and placental hormones

replace the ovarian hormones.

8-Give short notes on the following: a-Capacitation . B-Fertilizin-antifertilizin reaction.

A-Capacitation:

In mammalian forms, spermatozoa undergo a process called capacitation before they are fully capable of fertilizing the eggi.e. the capacity of spermatozoa to fertilize eggs of the same . As spermatozoa pass through the male reproductivetract, they are exposed to the decapacitating factor (DF) in the epididymis fluid or seminal plasm. Capacitation thusinvolves the removal of DF imposed on the sperm in the male reproductive tract.

The decapacitation factor performs the following functions:

a-prolongs the life of the spermatozoa.

b-Prevents the spermatozoa from penetrating the lining cells of male and female reproductive tracts.

c-Prevents sperm agglutination.

d-Prevents phagocytosis of sperm in the female reproductive tract. Recently, it has been found that the uterus secretes a uterine factor (glycosaminoglycan) which capacitated the sperm and make them capable of fertilizing ova.

B-Fertilizin-antifertilizin reaction: It has been found that

The egg water of unfertilized eggs has agglutinating

effect on spermatozoa from respective species.

There are two reacting substances namely fertlizin &

antifertilizin in eggs and spermatozoa respectively. The

fertilizin is a glycoprotein or mucopolysacchrides. Both

monosaccharides and aminoacids of fertilizin vary from

one species to another. The surface layer of cytoplasm

of the sperm (plasma membrane) contains another

species-specific protein called antifertilizn. Hence, the egg

fertilizin of one animal species will react and forms a

“chemical lock” only with antifertilizin of the sperm of

the same species.

9-Write on the acrosomal reaction and mechanism of sperm penetration in mammalian egg.

The penetration of the sperm through the egg membranes is achieved by certain enzymes in the acrosome. The egg membranes constitute barriers to prevent fertilization by more than one sperm or by sperm of alien species. In case of eggs with very thick membranes (e.g. insects and fishes), the sperm penetrates the resistant envelop through a special canal (micropyle) left in the egg membranes.

In mammals, the egg is surrounded by the plasma membrane outside of which there is a zona pellucida and a number of follicle cells forming the cumulus ooforus. The inner layer of the follicle cells are columnar in shape and form the corona radiata. During fertilization, the sperm must pass these membranes:

a-The outer follicle cells of cumulus oophorus are interspersed in a ground

substance that is a mucopolysaccharides containing hyaluronic acid.

Release of hyaluronidase from the acrosome breaks down the intercellular

connections of cells and allows the sperm to penetrate between them

b-Sperm in turn penetrates the corona radiata by releasing a second

enzyme called corona-penetrating enzyme (CPE) which also attacks

the ground substance.

c-The sperm penetrates zona pellucida by the action of another

enzyme secreted by the acrosome called trypsin-like enzyme

(TLE) or acrosin.

10- Give a detailed account of the cortical reaction.

2-The cortical reaction and formation of fertilization membrane:

When the eggs of sea urchin are inseminated, the first change

is the rupture of cortical granules and the discharge of their

contents at the egg surface. This is followed by the elevation

of the vitelline membrane and the formation of fluid-filled

perivitelline space.

The contents of thecortical granules swell and are then

discherged at the egg surface. The contents of the cortical

granules include enzymes, proteins and mucopolysacchrides.

The enzyme vitelline delaminase dissolves away the protein

that binds the vitelline

membrane to the plasma membrane of unfertilized egg.

As the mucopolysaccharides of the perivitelline space

swell, the vitelline membrane to lift away from the egg

surface.

The protein derived from contents of cortical granules

harden the vitelline membrane and transform it into the

fertilization membrane. Peroxidase and glucanase of

cortical granules may function in the hardening process.

11-Discuss the metabolic and synthetic activities after fertilization.

3- Metabolic and synthetic activities: If fertilization occurs, the eggs undergoes a series of rapid changes.

The fertilized egg shows changes in utilization of oxygen, permeability of plasmalemma, activities of enzymes and

synthesis of proteins.

A- It was found that oxygen consumption in sea urchin eggs increases after fertilization up to 600%.

B- An important change that occurs after fertilization is rapid increase of the calcium ions in the egg cytoplasm. This leads

to the change of permeability of the plasmalemma of the egg membrane. Sodium ions pass from outside into the

cytoplasm and hydrogen ions pass to the outside medium so that the surrounding medium becomes acidic and the egg

cytoplasm shifts to the alkaline side which is the real stimulus to development. The rise of the PH of the cytoplasm

initiates the synthesis of proteins and DNA in the egg, which are

needed for the increased nuclei during cleavage.

C-Among the metabolic changes that take place after fertilization

is the synthesis of proteins. In the sea urchin, the rise in protein

synthesis is rapid, about 30 fold increase in the rate of synthesis

occurs within 10 minutes after insemination. By contrast, studies

with mouse eggs show little significant increase in protein

synthesis upon insemination. Since amino acids and ribosomes are

present in both the unfertilized and fertilized eggs, the increased

protein synthesis after fertilization was thought to be due to new

quantities of messenger RNA emitted by the nucleus. However, it

was found that non-nucleated fragments of the egg can be

activated to parthenogenic development and such fragments show

an increase protein synthesis as in normal fertilized eggs. Thus

messenger RNA must be presnt, but inactive, in the unfertilized eggs.

12-Give short notes on migration and fusion of male and female pronuclei.

A-Migration:

At the time of penetration of spermatozoon inside the egg cytoplasm, the sperm nucleus remains compact and its

mitochondria and centriole remain situated behind it. To perform the process of fusion, the sperm nucleus performs

two activities:

(I) it has to become pronucleus.

(ii) it has to migrate from the site of fertilization to the site of fusion.

As the sperm nucleus moves inward from the site of fertilization cone, it

soon rotates through the angle of 180*, so that its mitochondria and

centriole assume the leading position. The sperm nucleus starts swelling

and its chromatin which is very closely packed, becomes finely granular.

It ultimately becomes vesicular and has an appearance like the interphase

nucleus and is called male pronucleus. At the same time, the sperm aster

forms in the egg cytoplasm around the proximal centriole of the sperm.

As the male pronucleus develops and migrates towards the site of fusion,

the sperm aster seems to lead it. The site of fusion lies either near the

center of microlecithal and mesolecithal eggs or in the center of cytoplasm

at the animal pole of macrolecithal and telolecithal eggs.

Before fusion , the nucleus of the egg also undergoes certain changes like the s

sperrm nucleus. After the completion of second meiotic division, the haploid nucleus of the egg occurs near the

surface of the egg in the form of several vesicles, known as karyomeres. In a fertilizing egg, these karyomeres fuse

together to form a female pronucleus which swells, increases in volume, and becomes vesicular. It also migrates

towards the site of fusion.

Fusion of pronuclei:

The actual fusion of the male and female pronuclei may differ in details in different animals. In most animals, the two

pronuclei actually fuse together, that is, the nuclear membrane of both pronuclei degenerates at the point of their

contact and the contents of both pronuclei unite into one mass which is bounded by a common nuclear membrane.

13-Mention the characterestics of the cleavage.

The splitting of an activated egg by a series of mitotic divisions into a multitude of cells which

become the building units of future organism, is called cleavage. The cleavage is characterized by

the following:

1-It divides the egg into an increasing number of cells of progressively decreasing size. The divisions

continue until the average cell size is similar to that of the differentiated cells of the parental

organism. The number of successive divisions depends on the volume of the egg compared with

the volume of typical somatic cells and on the availability of reserves, such as yolk.

The resultant cells are called blastomeres.

2-The shape of the embryo does not greatly change.

3-No growth occurs.

4-Chemical conversion of reserve food materials ( yolk, glycogen, etc.) into active cytoplasm containing

pool of amino acids, monosaccharides, lipid molecules and variety of enzymes, takes place. The

active cytoplasm ultimately transforms into nuclear substances ( molecules of DNA, RNA and

nucleoproteins) and those chemical molecules ( proteins, phospholipids, enzymes, etc. ) which are

needed as the building blocks in the formation of spindle, and nuclear and plasma membranes.

5-The constituent parts of ooplasm remain comparatively unaltered during cleavage, i.e. the

internal organization of ooplasm of the cleaved egg remains same as in the fertilized egg.

6-The ratio of nucleus to cytoplasm remains very low at the beginning of cleavage, but, at

the end of cleavage (blastula stage) it is brought to the level found in ordinary somatic cells.

7-The cleavage converts the egg into a compact mass of blastomeres called morula stage which

ultimately transforms into blastula, having unilayered thick blastoderm around a central

space called blastocoel.

14-Write an essay on the different patterns of cleavage.

1-Radial cleavage:

The radial cleavage occurs when the successive cleavage

planes cut straight through the egg, at right angles to one

another and the resulting blastomeres become

symmetrically disposed around the polar axis. When such

an egg is viewed from either pole, the blastomeres are found

to be arranged in a radially symmetrical form (e.g. all animals

having holoblastic cleavage).

2-Spiral cleavage:

The spiral cleavage is found in those forms in which there is a

rotational movement of cell parts around the egg axis. Hence, the upper

blastomeres come to lie not over the corresponding vegetal blastomeres

but over the junction between each two of the vegetal cells. In successive

cleavages, the rotational movements are characterized by a regular alternation

in clockwise or anticlockwise direction (e.g. annelids and molluscus).

3-Bilateral cleavage:

In some nematodes (Ascaris), the first division produces two unequal

cells: a slightly larger cell and a smaller one, thus establishing a plane

of bilateral symmetry in the developing embryo.

4-Superficial cleavage:

In centrolecithal egg of insects, the mitotic division of centrally located

nucleus is not followed by division of cytoplasm. The resulting nuclei,

each surrounded by a halo of cytoplasm, spread out in the undivided

layer of cytoplasm just beneath the surface.

15-Write an essay on the cleavage in placental mammals.

Cleavage in mammals is initiated in the upper end of the

oviduct, 24 hours after insemination. The mammalian egg

lacks synchronization of mitosis of blastomeres from the

two-celled stage onwards. Hence, the blastomeres are

divided into two types; blastomeres divide rapidly and

those divide slowly. The more rapidly dividing cells form

the trophoblast and the more slowly dividing cells form the

inner mass cells. Before entrance into uterine portion of

the oviduct the morula gradually becomes transformed

into the blastocyst and a large cavity or blastocoel is

formed with displacement of the inner cell mass toward

the future dorsal side of the embryo.

16-Write on the cleavage and blastulation in amphioxus.

In amphioxus, the first cleavage divides the egg

Into two equal blastomeres in a meridional plane

that extends from animal pole to the vegetal pole.

The second cleavage is also meridional but at the

right angles to the first furrow to form four equal

blastomeres. The third cleavage is horizontal and

slightly above the equator to form slightly smaller

four blastomeres(micromeres) toward the animal

pole and slightly larger four blastomeres

(macromeres) toward the vegetal pole.The fourth

cleavage is meridional with two furrows to form

sixteen blastomeres.The fifth cleavage is horizontal

dividing the eight micromeres and the eight

macromeres semultaneneously into a total of 32

blastomeres. During successive cleavages, the

larger macromeres in vegetal hemisphere tend

to divide more slowly than the smaller micromeres.

By the end of cleavage, the embryo is organized

as a hollow sphere ( blastula) whose cells enclose

a fluid-filled cavity, the blastocoel.

17-Discuss the cleavage and blastulation in amphibians.

The yolk is distributed along the animal-vegetal

axis with the greatest concentration at the vegetal

pole. Cleavage is initiated at the animal pole after

two hours of fertilization. The first two furrows are

meridional and at the right angles to each other

producing four cells of approximately equal size.

The first furrow passes through the grey crescent

so that each of resulting blastomeres contains a

portion of this cytoplasm. The unequal distribution

of the yolk within the egg leads to displacement of

third cleavage toward the animal pole. The

macromeres are confined to vegetal pole and the

micromeres to the animal pole. After about the 4th

or 5th cleavage, the regularity of segmentation

process is lost. Blastomeres containing yolk tend

to divide more slowly than those with less yolk.

After a short period, blastomeres are packed

together to form morula stage. The narrow cavities

between cells united to form a large cavity, the

blastocoel. In T.S., the cells of animal pole are

small and organized into two or more layers to form

the roof of blastocoel. The cells at the vegetal pole

are larger and form the floor of blastocoel.

18-Write on the meroblastic cleavage in birds.

In birds, the first cleavage is meridional and bisects the blastodisc

into partially separated blastomeres. The second cleavage

consists of two meridional furrows each one is at a right angle to

the first cleavage. The third set of cleavages are also vertical

parallel to the first cleavage furrow. The fourth set of cleavages

are vertical furrows to form eight central cells separated

from eight marginal cells. The centrally located cells have upper

and lateral surfaces but lacking a lower surface, so they are

continuous with yolk below. The marginal cells are incomplete

peripherally. From this point onward the succession o f cleavage

becomes irregular. In this cleavage, three types of furrows are

usually recognized:

a-Vertical furrows that extend peripheral toward the margin of

blastodisc.

b-Vertical furrows that cut across the inner ends of radiating furrows,

thereby producing peripheral boundaries to marginal cells; these

blastomeres then become part of centrally located cells.

c-Horizontal furrows that occur parallel to the surface and

established lower boundaries to the cells.

Horizontal cleavages begin after 32-celled stage.

By the time the embryo is organized as a mass of centrally located cells that lie over a fluid-filled cavity.

19-Write an essay on the superficial cleavage.• Superficial cleavage:

In the centrolecithal eggs, the nucleus is located at

the central part of egg and is surrounded by small

Amounts of cytoplasm. At first, division of nucleus

in the centre is not followed by division of the

cytoplasm so that a number of nuclei is produced

in the undivided central cytoplasm.

The nuclei migrate to the surface, each nucleus is

surrounded by a smaller portion of the central

cytoplasm which fuses with the superficial cytoplasm.

A syncytium is formed on the surface which then

becomes subdivided into cells or blastomeres.

These blastomeres are connected to the yolk

some time and then separated leaving a

compact yolk mass which is used up as a food

reserve by the developing embryo (e.g. insects)

20-Give a brief account of catabolic and anabolic activities during cleavage.• -Catabolic activities of cleavage:

• The cleavage requires large amount of chemical energy in the form of ATP molecules for its completion. For example, in each mitosis of cleavage, the microtubules of centrioles and mitotic spindle requires many ATP molecules to spend in the movements of chromosomes. These ATP molecules are manufactured in ooplasm and mitochondria during enzymatic anaerobic (glycolysis) and aerobic (Krebs cycle) oxidation of yolk, glycogen and other energy yielding chemical molecules of egg. The increased oxidation of a cleaving egg is correlated with increased input of oxygen molecules by the latter.

• B-Anabolic activities of cleavage:

• The qualitative growth during cleavage involves the biosynthesis of following kinds of macromolecules:

• i-Biosynthesis of DNA:

• During cleacage, the number of nuclei is doubled with every new division of the blastomeres and this increase is accompanied by an increase of nuclear substance , which in its turn involves an increase of DNA amount. The amount of DNA, however, remains constant per nucleus. In the S phase of interphase of each mitosis of cleavage, the DNA duplication occurs in the presence of an enzyme, called DNA polymerase. The precursor substances, such as, deoxyadenylate, deoxyguanylate, deoxycytidilate and thymidilate, all of which are deoxyribonucleotides, move from the cytoplasm to the egg nucleus and assemble into new polynucleotide strands of DNA polymerase enzyme.

• ii-RNA synthesis:

• During early cleavage, the chromosomal DNA remains hurriedly busy in its own duplication . The result is that no or little transcription of any kind of RNA occurs during this period. Hence, the messenger RNA and transfer RNA , however, are synthesized during cleavage or at least in the later stages of cleavage.

• iii-Protein synthesis:

• The cleaving egg requires different species of structural, enzymatic and regulator proteins for its diverse mode of functions. For example, the structural proteins are required as building blocks for different cellular membranes, egg cortex, microtubules, ribosomes etc. The enzymatic proteins are needed at different steps of cleavage for controlling the metabolism of cleavage as a whole. The regulator proteins (such as histone and non-histone proteins)remain associated with DNA molecule and are responsible for differential behavior of the latter during embryonic development.