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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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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