Molecular & genetic mechanisms of onto genesis

1. Molecular and
genetic
mechanisms of
ontogenesis.

2. PLAN
• Asexual and sexual reproductions in
unicellular and multicellular organisms
• Gametogenesis: spermatogenesis and
oogenesis
• Morphogenetic specialization of sex cells:
a sperm and an ovum
• Fertilization.
• The periods of ontogenesis

3. Reproduction
is the method by which
individuals give rise to
other individuals of
same type

4. There are two types of
reproduction
asexual
sexual

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6. Types of reproduction
asexual sexual
Organisms single-cellular organisms,
multi-cellular organisms:
one ore more somatic
cells of parental
organisms;
Parental organisms
forms gametes
Parents One person Two persons
Offspring's genetically identical to its
parent like a xero copy.
genetically different
from parents
Cell formation Mitosis Meiosis

7. Asexual is a reproduction without
the fusion of sexual cells,
identical offspring grows directly
from a one or few body cells,
which divides mitotically

8. Asexual Reproduction
• Involves the process of mitosis
• Offspring are genetically identical
to parent

9. Forms of asexual reproduction
in single-cellular organisms:
• binary fission – parent cell splits in two
cells by mitosis
• endogony -endogony - in parent cell forms only twoin parent cell forms only two
daughter cells by internal buddingdaughter cells by internal budding
• schizogony -schizogony - formation a great amount offormation a great amount of
daughter cells in parent celldaughter cells in parent cell

10. Binary Fission
2 daughter cells are identical to parent

13. asexual reproduction
• budding - after karyokinesis the special
region in parent cell rapid grows and
organized into new organism.
• sporogony -sporogony - is reproduction by theis reproduction by the
sporesspores

14. Budding

15. Forms of asexual reproduction in
multi-cellular organisms
• sporogony - is reproduction by the spores
• budding -parent produces a bud, bud gets
detached and develops into offspring
which is identical to parent
• polyembrionypolyembriony -- the production of two orthe production of two or
more embryo's from the one zygotemore embryo's from the one zygote

16. Spore Formation
Fungi
FernFern

18. Fragmentation
In this form, the body of the parent
breaks into distinct pieces, each of
which can produce an offspring.
Pieces of coral broken off in storms
can grow into new colonies.
A new starfish can grow from
one detached arm.

19. Asexual reproduction
• Vegetative – a group of cells from the
parent organism separates and new
organism forms

20. Tuber
Bulb
CormRhizome
Runner

21. Layering Grafting
scion
stock

22. Sexual reproduction
is a reproduction by
fusion of sexual cells and
formation of zygote

23. In sexual reproduction
genetic material from two individuals
combines to begin the life of a third
individual who has a new combination
of inherited traits

24. Forms of sexual reproduction
in single-cellular organisms
• Conjugation
• Copulation

25. Conjugation
a cytoplasm bridge forms between two
organisms, the nuclei transfer across this
bridge and after exchange ones forms a
new gene combination but no new
offspring

27. Copulation
two individuals acquire the
gametes properties, fuse and
form a zygote – the life of a new
individual begins

29. In multicellular organism sexual
reproduction may be two forms
- with fertilization
- without fertilization

30. Parthenogenesis
is the development of new organism from
an egg without fertilization

32. Methods of sexual reproduction:
Pollination
External Fertilization
Internal Fertilization

33. Sexual Reproduction in Plants
(Pistil)
Male Parts
Female Parts
pollen (male) + ovule (female) → single-celled zygote → multi-celled
embryo (contained in a seed) → new individual

34. External Fertilization
• External fertilization usually requires a
medium such as water, which the
sperms can use to swim towards the
egg cell. External fertilization usually
occur in fish and amphibians.
• The females lay the eggs in the water
and the male squirts the sperm
in the same area.

35. Internal Fertilization
• Fertilization occurs within the female.
• Internal fertilization occurs in mammals,
insects, birds, reptiles.

36. Sexual Reproduction in Animals
• involves specialized sex cells called gametes
• the union of a male and female gamete results in the
formation of a zygote that develops into a new individual

37. Sexual Reproduction Summary
MaleMale
GameteGamete
FemaleFemale
GameteGamete
Type ofType of
UnionUnion
Result ofResult of
UnionUnion
FinalFinal
ResultResult
PlantsPlants pollen ovule
(egg)
pollination single cell
zygote
multi-cell
embryo
(in seed)
AnimalsAnimals sperm egg fertilization single cell
zygote
multi-cell
embryo

38. Asexual
Reproduction
– involves only 1 parent
– offspring genetically
identical to parent
– involves regular body
cells
– its quick
Sexual
Reproduction
– involves 2 parents
– offspring genetic mix
of both parents
– involves specialized
sex cells
– its slow

39. Some Organisms do Both
• most plants that produce seeds (sexual
reproduction) can also reproduce
asexually by things like cuttings or runners
• this gives them an advantage for survival
sponges and hydra mosses

40. Gametogenesis
• process of formation and development of
sex cells
• the aim is to prepare sex cells to their
assimilation or fusion that is a basis of
fertilization
• during gametogenesis, the chromosome
number is reduced by half and shape of
cells is altered

41. Spermatogenesis
maturation process of male gametes; includes
the series of events leading to transformation
of spermatogonia into haploid spermatids;
these then develop into ripe (mature) sperms
by gradual process known as spermiogenesis
(= histological differentiation of spermatids)

43. Oogenesis
maturation process of female
gametes
is bound to the ovary (ovarian cortex) -
ovarian follicles
2 phases:
oocytogenesis
meiosis

45. Gametogenesis

46. Two types of sex cells are
distinguished:
• Male cell is spermatozoon or sperm
• Female cell is ovum or ovocyte

48. Distinguish the following
types of ovum cells:
• The isolecythal ovum contain a little yolk. It is
distributed in regular intervals on all cytoplasm
of an ovum.
(ovum of mollusca, lancelet, mammalian).
• The telolecythal ovum have much yolk of grains.
They collect at a vegetative pole. On animal
pole there is cytoplasm without yolk and with
nucleus.(ovum of fishes, amphibians, reptilie).
• The centrolecythal ovum has the central
nucleus and around it settles down yolk as
grains. (insects).

50. The fusion of haploid gametes to form a new
diploid cell is called fertilization or syngamy
During fertilization two processes take place:During fertilization two processes take place:
Egg’s activationEgg’s activation – a wave of chemical reactions sweeps across the– a wave of chemical reactions sweeps across the
surface of the newly aroused egg, causing that surface to harden andsurface of the newly aroused egg, causing that surface to harden and
present a barrier to the entry of any additional sperm. The egg’s oxygenpresent a barrier to the entry of any additional sperm. The egg’s oxygen
consumption skyrockets, as does its rate of protein synthesis.consumption skyrockets, as does its rate of protein synthesis.
SyngamySyngamy – male and female haploid nuclei converge and fuse to form– male and female haploid nuclei converge and fuse to form
the zygote’s single diploid nucleusthe zygote’s single diploid nucleus

52. Ontogenesis
• the development of the individual
organism.
• It includes the set of morphological,
phisiological and biochenical
transformations from the moment of
germing up to death.

53. The ontogenesis of multicellular
organisms is divided in two periods
1 embryonic
2 postembryonic.
For higher animals and man there are:
1) prenatal (before birth)
2) posnatal (after birth) periods of development

54. Human developmental periods
• Progenesis - is a period of
maturation of specialized
generative cells- gametes. This
maturation process is called
spermatogenesis in males and
oogenesis in female

55. Prenatal period
Prenatal period begins when an oocyte from female is fertilized
by a sperm from male with the formation of zygote.
Main stages of prenatal period:
• Fertilization is fusion of a female and male gamete.
• Cleavage is the series of rapid cell divisions of the zygote with
the formation of blastula
• Gastrulation is the formative process by which the three germ
embryonic layers are established in embryos (ectoderm,
mesoderm and endoderm).
• Formation of axial organs: notochord, neural tube, and
primordial gut.
• Histogenesis
• Organogenesis
• Systemogenesis

56. Kinds of cleavage:
• Holoblastic (total cleavage) – the zygote is divided
completely. There are 1) uniform and 2) irregular holoblastic
cleavage. They are haracteristic for isolecythal and
telolecythal cells
• Meroblastic (incomplete cleavage) – the part of cytoplasm of
an zygote is divided where yolk is absence.
There are: 1) discoidal and 2) superficial meroblastic
cleavage.
In discoidal meroblastic cleavage the segmentation occurs
on an animal pole in telolecythal cells. Birds’ eggs contain
so much yolk that the small disc of cytoplasm on the surface
is dwarfed by compasion. No cleavage of the massive yolk
is possible, and all cell division is restricted to the small
cytoplasmic disc, or blastodisc.
In superficial meroblastic cleavage the segmentation occurs
on an peripheric zone of cytoplasm in centrolecital cells.

58. In the man the cleavage of zygote is
holoblastic, irregular and asynchronous

59. - morula (from latin morus – mulberry) the solid ball
consisting of 12 to 16 blastomeres blastomeres = cells that
result in process of cleavage of the zygote, blastomeres are
genetic equal and they do not substantially differ each other,
prospective properties or developmental potency of
blastomeres are the same, each of them can give rise to a new
individuum
-

60. gastrula - the bilaminar pre-embryonic stage, in which the main
body axis and polarity begin to become apparent, the bilaminar
stage develops on day 7 and lasts to the end of the second week
after fertilization
blastocyst the stage with a cavity inside that is filled with fluid, 2
different cell populations differentiate at the first time in
development: trophoblast cells + inner cell mass or embryoblast
cells, during the day 5

62. Gastrulation - cell migrations to positions where they will
form the three primary cell layers:
1) ectoderm (outside germinal layer);
2) endoderm (inside germinal layer) and
3) mesoderm (medium germinal layer)

63. The germinal layers give rice
to various tissues and organs
of animals. It is called as
histogenesis and
organogenesis

64. The fate of primary germinal layers is given bellow:
Ectoderm Mesoderm Endoderm
Skin (epidermis),
hair, nails, the eye
lens, the pituitary
gland, the
epithelium of the
nasal cavity,
mouth, anal canal,
nervous system,
sense organs
Connective tissue, bones,
muscles, dermis, heart,
blood vessels, gonads,
excretory organs (kidneys)
and the notochord (the
dorsally located supportive
rod found in all chordates, at
least in embryonic stages)
Digestive tract,
lungs, liver,
pancreas, thyroid
gland, urinary
bladder

66. Mammalian Development
• 4 extraembryonic membranes form:
– chorion- from trophoblast, surrounds embryo and
all other membranes
– amnion- from epiblast, encloses embryo in
amniotic fluid
– yolk sac- from hypoblast, site of early blood cell
formation
– allantois- outpocketing of embryo’s gut,
incorporated into umbilical cord, forms blood
vessels of umbilical cord

67. • Provisional organs
are present during
embryonic period
and absent after
birth.
• Provisional organs
in human embryo
are:
an youlk sac
an amnion
an allantois
a chorion.

68. Placenta
• By the 23-rd day of human
embryonic development, two
other embryonic membranes
– the chorion and the
allantois to give rise to a
placenta
• Exchange of material takes
place in the placenta by
diffusion between the blood
of the mother and that of the
embryo
• Within the placenta there is
no mixing of maternal and
fetal blood

71. Types of ontogenesis in animals:
1. The larval type of an ontogenesis is characterized by
development of an organism by metamorphosis.
Metamorphosis – is change of shape or structure of an
organism from one developmental stage to another.
F/e mosquito: ovum- larva- pupa - imago;
louses – ovum- larva - imago;
pincers – ovum- larva- nymph - imago.
2. The non-larval type of an ontogenesis is characterized
by formation of an organism in
an egg (birds)
3. Intrauterine ontogenesis – is development of an
organism inside a maternal organism. (mammalian).

73. Phases of the postnatal development in the human
infancy – from the birth to the end of the first year of the age (the first two
weeks of infancy are called as the newborn or neonatal period)
childhood - from 13 month until 12 to 13 years; the primary teeth appear
and are replaced by the secondary or permanent teeth
puberty - is the period between 12-15 years in girls and 13-16 years in
boys, during which secondary sexual characteristics develop
adolescence - follows the puberty and ends 3-4 years after it; the
organism reaches sexual but also physical, mental and emotional maturity
adulthood - a period in which developmental changes occur very slowly
and are mostly characterized by selective loss of highly specialized cells
and tissues
postnatal development of the human is studied and treated with various
medical branches

74. In embrionic development of man there
are following critical periods:
• Implantation (7 day after a fertilization) – introduction of a
zygote in a wall of an uterus
• Placentation (the end of 2 week of pregnancy) – form at
embryo of a placenta
• Perinatal period (from 28 week of pregnancy to 7 day after
birth) – is transferring a fetus out of aqueous into air (on the
average, about 280 days after the beginning of the mother’s
last regular menstrual period).

75. • Any substance that can causes abnormal
development of is called a teratogen.