fertilization and maturation
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Fertilization and Maturation Stage
Exercise 2
First polar body
Oogonium (2N)
Primary Oocyte (2N)
Secondary Oocyte (N)
Growth / Maturation
Meiosis I
Meiosis II
Second polar bodiesOotid (N)
Ovum (N)
Differentiation
ovulation
Arrest at metaphase I until stimulated by hormone
FertilizationNo Fertilization
degeneration MII continues
Arrest at metaphase II
Slides to be studied: Ascaris uterus
Ascaris Parasitic nematodeAscaris eggs – transparent – possible to study steps in maturation, fertilization and cleavageSperm cells enter the eggs in the genital tract even before Meiosis I2N = 4
Unfertilized eggsVacuolated cytoplasminconspicuous nucleithin cell membranesPrimary oocytenote: staining in the picture is different from the staining of the slides in the labno pronuclei, no sperm head, just vacuolated cell
Stages of Maturation
Sperm Penetration StagePronuclear StageFusion StageEarly Cleavage
1. Sperm Penetration StageStage of Development: Primary oocytePresence of Bivalents Heads of spermatozoa – small, dense triangular bodiesAfter fertilization: forms fertilization membrane and outer shell (chitinous shell)
Chitinous shell
Fertilization Membrane
Perivitelline space
bivalents
Germinal Vesicle
or Female nucleus
Sperm head
Cell membrane
2. Pronuclear StageFemale Pronucleus – lightly stained/ transparentMale pronucleus – darkly stained; biggerFormation of First polar body
Separation of the homologous pairsFirst polar body extrudedStage of development: Secondary oocyte
Formation of Second polar bodiesSeparation of sister chromatids2nd polar body extruded ( 2 polar bodies will be seen; the outer one is the first and the inner one is the second polar body)Stage of development: Ootid
Chitinous shell
Fertilization Membrane
Perivitelline space
First Polar Body
Female Pronucleus
Male Pronucleus
Cell membrane
Stage of development: Secondary oocyte
Chitinous shell
Fertilization Membrane
Perivitelline space
Second Polar Body
Female Pronucleus
Male Pronucleus
Cell membrane
First Polar Body
Stage of development: ootid
3. Fusion StageFusion of the male and female pronuclei. (observe closely; it must be flat in the middle; there are cases when the male and female pronuclei seem to be fused but are actually just overlapping)
Presence of 2 polar bodies (inner- 2nd, outer- 1st) or 1 polar body (2nd polat body near the outer covering; 1st polar body already extruded from the shell)Perivitelline space – space between the egg and the fertilization membraneStage of development: Ovum
Chitinous shell
Fertilization Membrane
Perivitelline space
Second Polar Body
Fused Male and Female Pronuclei
Cell membrane
First Polar Body
Note: Discernment is needed to be able to distinguish the 1st and 2nd polar bodies. It is always the first polar body that is first extruded. The speed of the extrusion of polar bodies from the egg cell may vary, so in the fusion and early cleavage stage there may be 2, 1 or no polar body that can be observed.
Early Cleavage StageZygoteDiploidEntire cell dividing (contrast telophase to fusion stage)Observe the phases of mitosis (prophase, metaphase, anaphase, telophase)
Prophase
Metaphase
Anaphase
Telophase
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