1. Theme: Molecular and genetic mechanisms of ontogenesis
Theme: Molecular and genetic mechanisms of ontogenesis. Ontogenesis abnormalities
Lector Pryvrotska Iryna

2. Plan of the lecture:
Asexual reproduction in unicellular and multicellular organisms
Sexual reproduction in unicellular and multicellular organisms
The periods of ontogenesis
Spermatogenesis and oogenesis
Morphogenetic specialization of sex cells: a sperm and an ovum
Fertilization. Parthenogenesis
Biological peculiarities of human reproduction

3. Reproduction is the method by which individuals give rise to other individuals of same type.
There are two types of reproduction :
asexual and sexual

4. Types of reproduction asexual sexual Offspring's 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

5. Forms of asexual reproduction in single-cellular organisms:
Asexual is a reproduction without the fusion of sexual cells, identical offspring grows directly from a one or few body cells, which divides mitotically
binary fission – parent
cell splits in two cells by mitosis

6. Asexual reproduction
endogony - in parent cell forms only two daughter cells by internal budding
schizogony - formation a great amount of daughter cells in parent cell

7. Asexual reproduction
budding - after karyokinesis the special region in parent cell rapid grows and organized into new organism.
sporogony - is reproduction by the spores

8. Forms of asexual reproduction in multi-cellular organisms
vegetative (regeneration) – a group of cells from the parent organism separates and new organism forms

9. Asexual reproduction
polyembriony - the production of two or more embryo's from the one zygote
sporogony - is reproduction by the spores

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

11. Sexual reproduction
Forms of sexual reproduction in single-cellular organisms are
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.
Copulation - two individuals acquire the gametes properties, fuse and form a zygote – the life of a new individual begins.

12. In multicellular organism sexual reproduction may be two forms: with fertilization - without fertilization
Parthenogenesis is the development of new organism from an egg without fertilization.

13. 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.

14. Types of ontogenesis in animals:
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.
The non-larval type of an ontogenesis is characterized by formation of an organism in
an egg (birds)
Intrauterine ontogenesis – is development of an organism inside a maternal organism. (mammalian).

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

16. Germ cells
The ovum nourishes the embryo with yolk, which contains rich stores of lipids.
It provides the machinery for protein synthesis

17. An ovum is enormous in size
An ovum is enormous in size. It protects the developing embryo inside jellylike protein coatings and strong membranes (zona pellucida), sacs of fluid, and sometimes hard or leathery shells.
Corona radiata outside the cell consists of the great amount of follicular cells, which produce follicular fluid for attracting the sperms.

18. 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).

20. Unlike the egg, the sperm is one of the smallest cells in the body.
Each sperm consists of:
a head region
a body or midpiece
a tail or flagellum.
The head has a haploid nucleus. An acrosome – a small bump on the front end of the head contains enzymes that help the cell penetrate the ovum’s outer membrane.

21. Sperm cell
The body or midpiece has mitochondria to provide the cell energy and centrioles.
A tail consists of microtubules for propulsion.
The sperm’s streamlined size and shape effect its narrow objective: to reach the egg, penetrate its coating, and deliver a haploid nucleus into the egg’s cytoplasm

22. Oogenesis This process begins in a haploid oogonium.
An oogonium accumulates cytoplasm, replicates its chromosomes- primary oocyte.
In meiosis I, the primary oocyte divides to form a small polar body and a large, haploid secondary oocyte.

23. Oogenesis
Ovulation – dischange (going out) of a secondary oocyte from a follicule of the ovary.
In meiosis II, the secondary oocyte divides to yield another small polar body and a mature ovum. Therefore, each cell undergoing meiosis in female can potentially divide to yield a maximum of four cells, only one of which will become the ovum

24. Spermatogenesis Sperm development begins with spermatogonia.
A diploid spermatogonium divides mitotically and becomes a primary spermatocyte as it moves toward the lumen of the tubule.
In meiosis I- to form two secondary spermatocytes.
In meiosis II, each secondary spermatocyte divides to yield two equal – sized spermatids.
Therefore, each cell undergoing meiosis in male can potentially divide to yield a maximum of four spermatids.

25. Gametogenesis Reproduction Periods Spermatogenesis Oogenesis 2n2c 2n4c
Cells
Genetic formula
Reproduction
Cells divides mitoticaly
♂ - from puberty to death
♀- strongly at 3-7 m. in embryogeny completed at 3-d year
spermatogonia
2n2c 2n4c
oogonia
2n2c
2n4c

26. Growth primary spermatocyte 2n4c primary oocyte Cells Genetic formula
Cell growth and increase in size. Duplication of DNA.
primary spermatocyte
2n4c
primary oocyte

27. Maturation 1n2c mature ovum 1n1c
Cells
Genetic formula
Maturation
Meiosis I- cells halves genetically material
Meiosis II
two secondary spermatocytes
two spermatids
1n2c
1n1c
Secondary
Oocyte
mature ovum

28. Formation (spematogenesis)
Cells
Genetic formula
Formation (spematogenesis)
Spiralization of chromosomes, formation of acrosome,cell centre, tail
sperms
1n1c

29. Gametogenesis

30. Ontogenesis abnormalities 1) multynuclear oocytes; 2) 10% of sperms can be abnormal; 3) development of germ cells with 22 or 24 chromosomes

31. The fusion of haploid gametes to form a new diploid cell is called fertilization or syngamy
Fertilization may be external and internal

32. Fertilization During fertilization two processes take place:
Egg’s activation – a wave of chemical reactions sweeps across the surface of the newly aroused egg, causing that surface to harden and present a barrier to the entry of any additional sperm. The egg’s oxygen consumption skyrockets, as does its rate of protein synthesis.
Syngamy – male and female haploid nuclei converge and fuse to form the zygote’s single diploid nucleus

33. Fertilization 3 functions transmission of genes
restoration of the diploid number of chromosomes reduced during meiosis
initiation of development in offspring

34. Fertilization internal fertilization capacitation
sperm must penetrate cumulus and zona pellucida
extracellular matrix consisting of 3 types of glycoproteins one of these, ZP3, acts as a sperm receptor

36. Fertilization activates the egg, initiating metabolic processes
acrosomal reaction
sperm are activated
acrosomal process
sperm and egg membranes fuse
ion channels open, allowing Na+ to flow in
fast block to polyspermy
cortical reaction
egg’s ER releases Ca2+ into the cytosol at site of sperm entry

38. Fertilization slow block to polyspermy
Ca2+ causes cortical granules underneath the plasma membrane to fuse
mucopolysaccharides draw water into the space, swelling it
vitelline layer becomes the fertilization membrane

40. Cleavage rapid divisions following fertilization
often skip G1 and G2 phases
blastomeres result
most animal eggs have polarity
substances are heterogeneously distributed in cytoplasm
vegetal pole
animal pole

41. 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.

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

44. Mammalian Development
implantation
ICM forms flat disk with 2 layers (epiblast and hypoblast)
embryo develops from epiblast cells, hypoblast forms yolk sac
gastrulation

46. Gastrulation series of 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)

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

48. 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

50. 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

51. 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.

52. The youlk sac – the extraembryonic membrane that connects with the midgut. In human it is the first site of blood cell formation, but has no nutritive function.

53. Chorion [Gr. «membane»] – in human it is cellular, outermost extraembryonic membrane, composed of trophoblast lined with mesoderm, it develops villi about 2 weeks after fertilization, is vascularized by allantoic vessels a week later.

54. Amnion [Gr. «bowl» ; «membrane enveloping the fetus»] – the thin but tough extraembryonic membrane of reptilies, birds, and mammals that lines the chorion and contains the embryo and later the fetus, with the amniotic fluid around it.

55. 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

56. Human Gestation organogenesis fetus- all major structures are present
human chorionic gonadotropin (hCG)- produced by embryo, maintains corpus luteum
mucous plug formation in cervix
negative feedback- cessation of ovulation and menstrual cycles

57. Human Gestation 2nd trimester increased movement of fetus
hCG levels decline, leading to deterioration of corpus luteum
placenta secretes progesterone
uterus increases to visible size

58. Human Gestation 3rd trimester rapid growth of fetus
estrogens and oxytocin initiate labor
positive feedback- oxytocin stimulates prostaglandin secretion by placenta, leading to increased contractions

60. 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).

61. Intrauterine pregnancy

62. Any substance that can causes abnormal development of the egg in the mother's womb is called a teratogen.
Growth is rapid, and each body organ has a critical period in which it is especially sensitive to outside influences. About 7% of all congenital defects are caused by exposure to teratogens.
Drugs
Alcohol.

63. Ontogenesis abnormalities
Chances of Down syndrome rapidly increase with parental age starting at about age 35 in women and 55 in men. Previously, it was thought there might be a tendency toward nondisjunction as a women ages because her eggs age as she does - a women is born with all the eggs she will ever have and they remain in suspended animation until one matures each month.

64. Ontogenesis abnormalities

66. References: 1. Biology. – Sylvia S. Mader, Wm. C
References: 1. Biology. – Sylvia S. Mader, Wm. C. Brown Publishers: Dubuque, Lowa – Melbourne, Australia – Oxford, England, IV edition. – p , Biology. Art notebook – Sylvia S.Mader, Wm. C. Brown Publishers: Dubuque, Lowa – Melbourne, Australia – Oxford, England, IV edition. – p Human biology. – McMillan, Beverly. – p