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. 12/18/2014 10

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

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