gametogenesis and fertilization
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Embryology Gametogenesis and fertilizationTRANSCRIPT
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Gametogenesis and fertilization
ByDr. Ansari
Chairperson & Prof. AnatomyRAKCODS. RAKMHSU
(for BDS students)
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The learning outcomes are
• The students are able to chart out the steps in Gametogenesis occurring in male persons and steps of oogenesis occurring in female subjects.
• The result of spermatogenesis and spermiognenesis.
• The result of oogenesis.• The fertilization is the result of union between
the male and female gametes occurring in the female reproductive organs.
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Formation of male gametes is called spermatogenesis
• It occurs in the testis of an adult male.• The mother cells are called as spermatogonia.• Each spermatogonium consists of 2n number of
chromosomes. • In human it is 46 chromosomes (22autosomes
and XX/XY sexosomes).• The supporting cells are called as sertoli cells.• They help in providing nutrition and helps in
spermiognenesis-maturation of sperms.
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There are three steps in spermatogenesis
• 1) Meiosis I, during which the number of chromosomes in the cell is reduced to half or 23 chromosomes each;
• 2) Meiosis II, during which each haploid cell forms spermatids; and
• 3) Spermiogenesis, during which each spermatid develops into a sperm cell with a head and tail.
• The entire process of spermatogenesis takes about 64 days.
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The spermiogensis is regulated by Sertoli cells
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The oogenesis occur in female reproductive organ- ovary
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The fertilization is the union of male and female gametes-it occurs in uterine tubes
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The result of fertilization• Stimulates the secondary oocyte to complete meiosis.
• Restores the normal diploid number of chromosomes (46).
• Results in variation of human species as maternal and paternal chromosomes intermingle.
• The embryo contains only maternal mitochondria because the sperm mitochondria are dispersed into the egg cytoplasm and discarded.
• Determines the sex of the embryo.
• The sex chromosome (Y or X) carried by the successful sperm determines embryonic sex.
• The sperm can only survive 48 hours within the female genital tract.
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Monozygotic twin
• A fertilized, single egg splits into two developing zygotes at a very early stage.
• Identical twins; same sex.
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Dizygotic twin:-
• Result from the fertilization by two sperms & two separate ova that have reached maturation at the same time.
• Not identical twins; can be different sexes
• Incidence increases with age of the mother
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Conjoint twins- Siamese twins
• Conjoint twins will result when the germ disk duplicates itself and will not get separated out at a particular point and remain joined.
• Whole two individuals will develop with parts attached with each other.
• Here it is a craniopagus.
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References
• http://education-portal.com/academy/lesson/oogenesis-how-the-female-reproductive-system-produces-eggs.html#lesson
• http://www.youtube.com/watch?v=BFrVmDgh4v4
• http://www.tutorsglobe.com/getanswer/process-of-fertilization-in-human-beings-908778.aspx