This document discusses gametogenesis and fertilization in humans. It describes the processes of spermatogenesis in males, where spermatogonia undergo meiosis to form spermatids over 64 days, and oogenesis in females. Fertilization occurs when a sperm and egg unite in the uterine tubes, restoring the diploid chromosome number and determining the embryo's sex. The result can be a single embryo, or monozygotic or dizygotic twins in rare cases of splitting or separate eggs being fertilized.

1. Gametogenesis and fertilization
By
Dr. Ansari
Chairperson & Prof. Anatomy
RAKCODS. RAKMHSU
(for BDS students)
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2. 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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3. 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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4. 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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6. The spermiogensis is regulated by
Sertoli cells
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7. The oogenesis occur in female
reproductive organ- ovary
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8. The fertilization is the union of male and
female gametes-it occurs in uterine tubes
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10. 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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11. Monozygotic twin
• A fertilized, single egg
splits into two
developing zygotes at a
very early stage.
• Identical twins; same
sex.
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12. 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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13. 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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14. References
• http://education-portal.
com/academy/lesson/oogenesis-how-the-
female-reproductive-system-produces-eggs.
html#lesson
• http://www.youtube.com/watch?v=BFrVmDg
h4v4
• http://www.tutorsglobe.com/getanswer/proc
ess-of-fertilization-in-human-beings-
908778.aspx
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