Gametogenesis is the process by which haploid gametes are formed from diploid germ cells in the gonads. There are two types: spermatogenesis and oogenesis. Spermatogenesis occurs in the testes and involves the formation of sperm from spermatogonia over 74 days, involving multiplication, growth, and maturation phases. Oogenesis occurs in the ovaries and also involves three phases to form ova from oogonia. The resulting gametes, sperm and ovum, differ in structure according to their roles in fertilization. Sperm are small, motile cells specialized for movement, while ovum are larger stationary cells specialized to receive sperm and support development.

1. GAMETOGENESIS

2. GAMETOGENESIS
It is the process of formation and
differentiation of haploid gametes (
sperms and ova ) from the diploid primary
germs cells, gametogonia ( spermatogonia
and oogonia ) present in primary sex organs
called gonads ( testes in male and ovaries in
female respectively ).

3. 1 Spermatogenesis
2 Oogenesis
Types

4. 1 SPERMATOGENESIS
Definition :-
It is the formation of haploid,
microscopic and functional male
gametes, spermatozoa, from the
diploid reproductive cells,
spermatogonia, present in the testes of
male organism.

5. Period : In the seasonally breeding animals, the testes
undergo testicular cycle in which the testes and their
spermatogenic tissue become functional only in the
specific breeding season. So in some seasonally breeding
mammals like bat, otter, llama, testes enlarge, become
functional and descend into the scrotum in the breeding
season while become reduced , non-functional and
ascend into the abdomen in other seasons. But in
human male, lion, bull, horse etc. the testes lie
permanently in the scrotum and spermatogenesis
occurs throughout the year. But in some mammals like
elephant , echidna, dolphin, whale, seal etc. testes lie
permanently in the abdomen.
Spermatogenesis is a continuous process and is
completed in about 74 days.

6. MECHANISM
Spermatogenesis is divided into two parts.
1. Formation of spermatid
2. Spermiogenesis

7. IT IS DIVIDED INTO
THREE PHASES
Formation of
spermatid
Multiplicative
phase
Growth
phase
Maturation
phase

9. Structure of
spermatid
1. Nucleus
2 Golgi body
3 Distal centriole
4 Mitochondria
5 Cytoplasm
Changes in the
sperm
Shrinks and elongated
Changes to acrosome
Forms axial filament of sperm
tail
Form mitochondrial spiral of
sheath called nebenkern
Generally lost except a thin
sheath called manchette
CHANGES IN SPERMATID TO FORM SPERM DURING
SPEERMIOGENESIS

10. OOGENESIS
Definition: it involves the formation
of haploid female gametes called
ova, from the diploid egg mother
cells, oogonia of ovary of female
organism.

11. Multiplicative
phase
Growth
phase
Maturation
phase
Mechanism: like spermatogenesis, oogenesis
is formed of three phases

15. STRUCTURE OF GAMETES
 A. Sermatzoan ( Sperma = seed, zoon = animal )
 Definition: A spermatozoan is a haploid male gamete whose primary
function is to fuse with ovum to restore diploidy and to transmit
paternal characters to the offsprings.
 Structure. A mammalian sperm is minute, microscopic, flagellated and
motile gamete with no nutritive material, protective envelopes and
most of cell – organelles like ribosome, endoplasmic reticulum, etc. The
whole body of sperm is enveloped by plasma membrane only.
1. Head : Shape of head varies in different mammals. It is generally oval
and flat ( in man, bull, rabbit ). Basically the head is formed of two
parts.
Acrosome :small cap-like pointed structure present at the tip of nucleus.
During the sperm entry, the acrosome secretes a lytic enzyme, called
Hyaluronidase, which helps in the penetration of ovum.

17. Nucleus: It is generally long, narrow and pointed but is flat
and oval in human sperm. It is formed by condensation of
nucleus chromatin of spermatid and lo of RNA, nucleolus and
acidic proteins.
2. Neck : It is the smallest part of spermatozoan and may be
indistinct. It is formed of two centrioles perpendicular to each
other and is formed from the centrosome of spermatid.
3. Middle piece : It lies behind the neck and is cylindrical in the
human sperm. It is formed of a mitochondrial spiral. The
mitochondrial are the carriers of the oxidative enzyme and the
enzymes which are responsible for oxidative phosphorylation.
So the middle piece is the powerhouse of a sperm.

18. 4. Tail: It is the longest part of sperm. It is slender
and tapering part. It is formed of two parts: central,
contractile and microtubular part called axoneme or
axial filament , and outer protoplasmic sheath.
Tail shows lashing movements which provide
forward push to the sperm.

19. B. OVUM
Ovum is a maternal haploid gamete and is primarily
concerned with receiving the sperm and is determined to
develop into a fully developed multicellular organism after
fertilization ( syngamy) or without fertilization
( parthenogenesis).

20. Structure
An ovum is generally spherical, non- motile gamete
with yolky cytoplasm and enclosed in one or more egg
envelops. Size of ovum varies from 10 µm to a few cm.
Egg Envelop: Human ovum is surrounded by a number
of egg envelop:
1. Vitelline membrane. It is inner, thin, transparent
and is secreted by ovum itself.
2. Zona pellucida. It is middle, thick, transparent and
non cellular.
3. Corona radiata. It is outer, thicker coat formed of
radially elongated follicular cells

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