Basic concepts Developmental biology 4th sem.ppt

this ppt contains basics of embryology

2. Definition :
Embryology : study of embryos.
From sexual reproduction gametes are
produced.
Embryo is juvenile of an organism.

3. SOME TERMS
Gamete: egg or sperm
Gametogenesis: production of eggs or
sperm
Oogenesis: production of eggs
Spermatogenesis: production of sperm
Spermiogenesis: differentiation of sperm
morphology
Follicle: where eggs mature in the ovary
Ovulation: release of egg from follicle
Polar body: nonfunctional product of
meiotic divisions in oogenesis
Zygote: Fertilized egg

4. SOME MORE TERMS
Oogonia: mitotically dividing cells in the
ovary, will become Oocytes
Primary oocyte: decision has been made
to undergo meiosis, cell has grown. Cells
are arrested at this stage until puberty.
Secondary oocyte: has completed first
meiotic division the division was unequal
in terms of cytoplasm
Ovum: Ovulated egg, ready to be
fertilized. If fertilized, the second
meitoic division will occur, another polar
body will be given off.

5. Theories of embryology:
Preformation theory
Epigenesis
Baer’s Law
Biogenetic law: “ontogeny recapitulates
phylogeny”

6. Phases of development of an organism:
Gametogenesis
Fertilization
Cleavage
Blastula
Gastrulation
Organogenesis
Growth
Differentiation
Metamorphosis

7. Gametogenesis :
Formation of gametes( sex cells, gametes, germ
cells)
Two types:
Spermatogenesis and Oogenesis.

8. Spermatogenesis :
Production of sperm
Results in four haploid sperm from each diploid cell that
undergoes meiosis.
a. Undifferentiated germ cells called spermatogonia
(diploid) undergo mitosis to produce daughter cells called
primary spermatocytes.
b. The primary spermatocytes undergo meiosis 1 to produce
haploid secondary spermatocytes in a duplicated state.
c. The sister chromatids of each chromosome separate from
each other during meiosis II. The daughter cells are
haploid spermatids.
d. The spermatids will then eventually mature into functional
sperm cells.
e. Sertoli cells provide the cells with nourishment and
molecular signals.

12. Spermiogenesis :
Transformation of spermatid to spermatozoa
Loss of cytoplasm, loss of RNA
Nucleus shape change, shrinkage
Acrosome formed from golgi bodies
Centrosome splits, centriole forms basal granule
Sperm formed, devoid of stored food, envelope,
distinguished into: head, neck, middle piece and
tail.

13. Oogenesis :
 A normal baby girl has about 2 million primary oocytes in her ovaries.
 By 7 years old about 300,000 remain, her body reabsorbed the rest.
a. Primary oocytes have already entered meiosis I, but the nuclear
division is arrested in a genetically programmed way.
 Meiosis will resume in one oocyte at a time, starting with the first
menstrual cycle.
 Only about 400 to 500 oocytes will be released during her reproductive
years.
 Follicle – primary oocyte and nourishing cell layers around it.
b. Stimulated by hormones the follicle continues to grow and the primary
oocyte completes meiosis I. Resulting in the formation of a secondary
oocyte (ends up with most of the cytoplasm) and the first of three
polar bodies.
c. Ovulation then occurs releasing the secondary oocyte and the polar
body.
d. Penetration of the sperm induces the secondary oocyte and the first polar
body to complete meiosis II. There are now three polar bodies and one
mature egg or ovum.
 As the sperm and egg nuclei fuse, their chromosomes restore the
diploid number for a brand new zygote.

17. Fertilization :